diff --git a/open-sse/config/searchRegistry.ts b/open-sse/config/searchRegistry.ts
index e4d4546212..3e9105ad35 100644
--- a/open-sse/config/searchRegistry.ts
+++ b/open-sse/config/searchRegistry.ts
@@ -33,6 +33,17 @@ export interface SearchProviderConfig {
    */
   fallbackOnly?: boolean;
   disabled?: boolean;
+  /**
+   * May a CALLER-supplied `provider_options.baseUrl` redirect this provider?
+   *
+   * Only ever true for a keyless, self-hosted provider. For anything with
+   * `authType: "apikey"` the builder attaches the OPERATOR's key to whatever
+   * host the base URL resolves to, so honoring a caller-chosen value hands that
+   * key to the caller's server (GHSA-3f8g-pfh9-j687). The invariant
+   * "never set alongside authType: apikey" is enforced by
+   * tests/unit/search-baseurl-client-override-3f8g.test.ts.
+   */
+  allowClientBaseUrlOverride?: boolean;
 }
 
 export const SEARCH_PROVIDERS: Record<string, SearchProviderConfig> = {
@@ -232,6 +243,11 @@ export const SEARCH_PROVIDERS: Record<string, SearchProviderConfig> = {
     timeoutMs: 10_000,
     cacheTTLMs: 3 * 60 * 1000,
     fallbackOnly: true,
+    // Keyless and self-hosted by definition: the caller names their own SearXNG
+    // instance and no operator credential travels with the request. This is a
+    // documented flow (tests/unit/search-route.test.ts). Still block-metadata
+    // guarded, so IMDS stays unreachable.
+    allowClientBaseUrlOverride: true,
   },
 
   "ollama-search": {
diff --git a/open-sse/handlers/search.ts b/open-sse/handlers/search.ts
index b1397f3c5d..e68603e459 100644
--- a/open-sse/handlers/search.ts
+++ b/open-sse/handlers/search.ts
@@ -20,6 +20,9 @@ import { randomUUID } from "crypto";
  * }
  */
 
+export { resolveSearchBaseUrl, SearchBaseUrlOverrideError } from "./search/baseUrl.ts";
+import { resolveSearchBaseUrl } from "./search/baseUrl.ts";
+
 import {
   getSearchProvider,
   isUnconfiguredLoopbackSearchProvider,
@@ -36,7 +39,6 @@ import * as anysearchSearch from "./search/anysearchSearch.ts";
 import { freeWebSearch } from "../services/freeWebSearch.ts";
 import { saveCallLog } from "@/lib/usageDb";
 import { safeOutboundFetch } from "@/shared/network/safeOutboundFetch";
-import { parseAndValidateNonMetadataUrl } from "@/shared/network/outboundUrlGuard";
 import { Client } from "@modelcontextprotocol/sdk/client/index.js";
 import { StreamableHTTPClientTransport } from "@modelcontextprotocol/sdk/client/streamableHttp.js";
 import { z } from "zod";
@@ -319,25 +321,6 @@ function getProviderSettingString(
   return undefined;
 }
 
-export function resolveSearchBaseUrl(
-  config: SearchProviderConfig,
-  params: SearchRequestParams
-): string {
-  const override = getProviderSettingString(params, "baseUrl");
-  if (override) {
-    // GHSA-j7j4-g9qc-q69c: the override is client-controlled (provider_options /
-    // providerSpecificData) and flows into a plain fetch() sink — validate it
-    // before any builder uses it as the server-side fetch target. Mode is
-    // block-metadata (NOT public-only): the primary searxng use case is a
-    // self-hosted instance on loopback/LAN, so private hosts keep working,
-    // while cloud-metadata endpoints (IMDS credential theft) are rejected.
-    // The catalog's own config.baseUrl is operator config and stays untouched.
-    parseAndValidateNonMetadataUrl(override);
-    return override.replace(/\/+$/, "");
-  }
-  return config.baseUrl.replace(/\/+$/, "");
-}
-
 function toSearchPageNumber(offset: number | undefined, maxResults: number): number | undefined {
   if (typeof offset !== "number" || offset <= 0 || maxResults <= 0) return undefined;
   return Math.floor(offset / maxResults) + 1;
diff --git a/open-sse/handlers/search/baseUrl.ts b/open-sse/handlers/search/baseUrl.ts
new file mode 100644
index 0000000000..ba1e1fe6b0
--- /dev/null
+++ b/open-sse/handlers/search/baseUrl.ts
@@ -0,0 +1,66 @@
+/**
+ * Base-URL resolution for /v1/search — the trust decision, on its own.
+ *
+ * The two override sources are NOT equally trusted, and reading them through
+ * one call is what produced GHSA-3f8g-pfh9-j687:
+ *
+ *   - `providerSpecificData` is the stored provider connection
+ *     (`credentials?.providerSpecificData`) — OPERATOR config. Honored under
+ *     block-metadata, so a self-hosted SearXNG on loopback/LAN keeps working
+ *     while cloud metadata (IMDS credential theft) stays rejected (GHSA-j7j4).
+ *   - `providerOptions` is `body.provider_options` — CALLER input. Honored only
+ *     by a provider that is keyless AND opted in via
+ *     `allowClientBaseUrlOverride`. A keyed builder attaches the OPERATOR's key
+ *     to whatever host this resolves to (`key=`/`api_key=` in the query for
+ *     google-pse/searchapi, `X-API-Key`/`Authorization` for
+ *     you.com/linkup/nimble/ollama), so a caller-chosen host would collect it —
+ *     and a block-metadata check does nothing about that, because the attacker
+ *     simply names their own public host.
+ *
+ * Full coverage: tests/unit/search-baseurl-client-override-3f8g.test.ts.
+ */
+
+import { parseAndValidateNonMetadataUrl } from "@/shared/network/outboundUrlGuard";
+import type { SearchProviderConfig } from "../../config/searchRegistry.ts";
+
+interface BaseUrlParams {
+  providerOptions?: Record<string, unknown>;
+  providerSpecificData?: Record<string, unknown>;
+}
+
+/** Read one string setting from a SINGLE source, so callers can distinguish trust. */
+function readSetting(source: Record<string, unknown> | undefined, key: string): string | undefined {
+  const value = source?.[key];
+  return typeof value === "string" && value.trim().length > 0 ? value.trim() : undefined;
+}
+
+/** Refusal for a caller-supplied `provider_options.baseUrl` (GHSA-3f8g-pfh9-j687). */
+export class SearchBaseUrlOverrideError extends Error {
+  readonly code = "SEARCH_BASE_URL_OVERRIDE_REFUSED";
+  constructor(providerId: string) {
+    super(
+      `provider_options.baseUrl is not accepted for search provider "${providerId}". ` +
+        `Set the base URL on the provider connection instead.`
+    );
+    this.name = "SearchBaseUrlOverrideError";
+  }
+}
+
+export function resolveSearchBaseUrl(config: SearchProviderConfig, params: BaseUrlParams): string {
+  const operatorOverride = readSetting(params.providerSpecificData, "baseUrl");
+  if (operatorOverride) {
+    parseAndValidateNonMetadataUrl(operatorOverride);
+    return operatorOverride.replace(/\/+$/, "");
+  }
+
+  const callerOverride = readSetting(params.providerOptions, "baseUrl");
+  if (callerOverride) {
+    if (!config.allowClientBaseUrlOverride || config.authType === "apikey") {
+      throw new SearchBaseUrlOverrideError(config.id);
+    }
+    parseAndValidateNonMetadataUrl(callerOverride);
+    return callerOverride.replace(/\/+$/, "");
+  }
+
+  return config.baseUrl.replace(/\/+$/, "");
+}
diff --git a/open-sse/utils/error.ts b/open-sse/utils/error.ts
index 4fafd05b1a..66563c618f 100644
--- a/open-sse/utils/error.ts
+++ b/open-sse/utils/error.ts
@@ -40,8 +40,36 @@ function looksLikeAbsolutePath(tok: string): boolean {
   return (SOURCE_EXT as readonly string[]).includes(ext);
 }
 
+/**
+ * Raw credential shapes that carry no `key=` label to key off — the token IS the
+ * whole match, so the only way to redact them is to recognize the shape.
+ *
+ * GHSA-qv45-56jc-4wmj: `upstreamErrorPassthrough.ts` already recognized `sk-`
+ * and refused verbatim passthrough for bodies containing it, then handed those
+ * bodies to THIS sanitizer — which had no such pattern, so the key came back to
+ * the caller anyway. The passthrough file's comment claimed to "mirror the
+ * vocabulary of redactSensitiveErrorText"; the mirror had drifted. It now
+ * imports this array instead of keeping a second copy, so the two cannot drift
+ * again.
+ *
+ * Quantifiers are upper-bounded (AGENTS.md → PII learnings §1, ReDoS): these run
+ * over untrusted upstream error bodies.
+ */
+export const RAW_CREDENTIAL_PATTERNS: ReadonlyArray<RegExp> = [
+  // OpenAI/Anthropic/Stripe-style secret keys: sk-…, sk-ant-…, sk_live_…
+  /\bsk[-_][A-Za-z0-9._-]{8,200}/g,
+  // Google API keys
+  /\bAIza[A-Za-z0-9_-]{20,200}/g,
+  // JWTs (three base64url segments)
+  /\beyJ[A-Za-z0-9_-]{8,400}\.[A-Za-z0-9_-]{8,800}\.[A-Za-z0-9_-]{8,800}/g,
+];
+
 export function redactSensitiveErrorText(value: string): string {
-  return value
+  let out = value;
+  for (const pattern of RAW_CREDENTIAL_PATTERNS) {
+    out = out.replace(pattern, "[REDACTED_CREDENTIAL]");
+  }
+  return out
     .replace(/data:[^,\s]+;base64,[A-Za-z0-9+/=_-]+/gi, "[REDACTED_DATA_URL]")
     .replace(/\b(Bearer|Basic)\s+[A-Za-z0-9._~+/=-]+/gi, "$1 [REDACTED]")
     .replace(
diff --git a/open-sse/utils/upstreamErrorPassthrough.ts b/open-sse/utils/upstreamErrorPassthrough.ts
index 21d0c6c964..b62fff2adf 100644
--- a/open-sse/utils/upstreamErrorPassthrough.ts
+++ b/open-sse/utils/upstreamErrorPassthrough.ts
@@ -1,3 +1,4 @@
+import { RAW_CREDENTIAL_PATTERNS } from "./error.ts";
 /**
  * Selective upstream 4xx error passthrough (Claude Code auto-recover contract).
  *
@@ -24,8 +25,23 @@ const INTERNAL_LEAK_RE = /\sat\s\/|node_modules|omniroute\//i;
 // caller fall back to the sanitized buildErrorBody path. Bodies without a
 // secret (the overwhelming majority, carrying capability/quota wording) still
 // relay verbatim. Mirrors the vocabulary of redactSensitiveErrorText in error.ts.
-const CREDENTIAL_LEAK_RE =
-  /\b(?:Bearer|Basic)\s+[A-Za-z0-9._~+/=-]{8,}|\bsk-[A-Za-z0-9._-]{8,}|(?:api[_-]?key|access[_-]?token|refresh[_-]?token|authorization|cookie|secret)\\?["']?\s*[:=]\s*\\?["']?[^"'\\,\s}]{6,}/i;
+const LABELLED_CREDENTIAL_RE =
+  /\b(?:Bearer|Basic)\s+[A-Za-z0-9._~+/=-]{8,}|(?:api[_-]?key|access[_-]?token|refresh[_-]?token|authorization|cookie|secret)\\?["']?\s*[:=]\s*\\?["']?[^"'\\,\s}]{6,}/i;
+
+/**
+ * The raw-token shapes (sk-…, AIza…, JWT) come from error.ts's
+ * RAW_CREDENTIAL_PATTERNS rather than a second local copy. The previous local
+ * copy carried `sk-` while the sanitizer this file falls back to did NOT, so a
+ * body recognized as leaky here was returned unredacted there
+ * (GHSA-qv45-56jc-4wmj). One source, no drift.
+ */
+function containsCredential(text: string): boolean {
+  if (LABELLED_CREDENTIAL_RE.test(text)) return true;
+  return RAW_CREDENTIAL_PATTERNS.some((pattern) => {
+    pattern.lastIndex = 0; // the shared patterns are /g — reset before .test()
+    return pattern.test(text);
+  });
+}
 
 export function shouldPassthroughUpstreamError(statusCode: number, upstreamBody: unknown): boolean {
   if (statusCode < PASSTHROUGH_MIN || statusCode > PASSTHROUGH_MAX) return false;
@@ -34,7 +50,7 @@ export function shouldPassthroughUpstreamError(statusCode: number, upstreamBody:
   const text = JSON.stringify(upstreamBody);
   if (INTERNAL_LEAK_RE.test(text)) return false;
   // Refuse passthrough when the provider echoed a credential back to us.
-  if (CREDENTIAL_LEAK_RE.test(text)) return false;
+  if (containsCredential(text)) return false;
   return true;
 }
 
diff --git a/open-sse/utils/upstreamResponseHeaders.ts b/open-sse/utils/upstreamResponseHeaders.ts
index 834d354f18..9f6c16d1e6 100644
--- a/open-sse/utils/upstreamResponseHeaders.ts
+++ b/open-sse/utils/upstreamResponseHeaders.ts
@@ -45,3 +45,36 @@ export function filterUpstreamResponseHeaderEntries(
 }
 
 export const STRIP_UPSTREAM_HEADER_NAMES: ReadonlySet<string> = STRIP_HEADER_NAMES;
+
+/**
+ * Response headers that must never be relayed back to a client.
+ *
+ * A relay sends its own credential upstream (the bifrost route sends
+ * `Authorization: Bearer ${BIFROST_API_KEY}` to the sidecar). If that upstream
+ * echoes the header back — or sets its own session cookie — copying the response
+ * headers wholesale hands it to whoever holds the relay token
+ * (GHSA-9m72-44hg-w32g). `set-cookie` matters as much as `authorization`: it is
+ * a session, and the browser would store it against OUR origin.
+ */
+const SENSITIVE_RESPONSE_HEADER_NAMES: ReadonlyArray<string> = [
+  "authorization",
+  "proxy-authorization",
+  "x-api-key",
+  "x-goog-api-key",
+  "api-key",
+  "cookie",
+  "set-cookie",
+];
+
+/**
+ * New Headers with the stale framing set AND any echoed credential/session
+ * header removed. Use this instead of `new Headers(upstream.headers)` on every
+ * path that relays an upstream response to a client. Does not mutate the input.
+ */
+export function stripSensitiveResponseHeaders(input: Headers): Headers {
+  return new Headers(
+    filterUpstreamResponseHeaderEntries(input.entries(), SENSITIVE_RESPONSE_HEADER_NAMES)
+  );
+}
+
+export { SENSITIVE_RESPONSE_HEADER_NAMES };
diff --git a/src/app/api/v1/relay/chat/completions/bifrost/route.ts b/src/app/api/v1/relay/chat/completions/bifrost/route.ts
index 31b007959f..8674125c38 100644
--- a/src/app/api/v1/relay/chat/completions/bifrost/route.ts
+++ b/src/app/api/v1/relay/chat/completions/bifrost/route.ts
@@ -29,9 +29,14 @@
  */
 
 import { CORS_HEADERS, handleCorsOptions } from "@/shared/utils/cors";
+import { stripSensitiveResponseHeaders } from "@omniroute/open-sse/utils/upstreamResponseHeaders";
 import { createInjectionGuard } from "@/middleware/promptInjectionGuard";
 import { getRelayTokenByHash, checkRateLimit, recordRelayUsage } from "@/lib/db/relayProxies";
-import { buildErrorBody } from "@omniroute/open-sse/utils/error";
+import {
+  buildErrorBody,
+  parseUpstreamError,
+  sanitizeErrorMessage,
+} from "@omniroute/open-sse/utils/error";
 import { getProviderPluginManifestHeader } from "@omniroute/open-sse/config/providerPluginManifestUrl.ts";
 import { z } from "zod";
 import {
@@ -299,7 +304,11 @@ export async function POST(request: Request) {
       });
     };
 
-    const newHeaders = new Headers(upstream.headers);
+    // Never copy the upstream headers wholesale: the sidecar receives our
+    // `Authorization: Bearer ${BIFROST_API_KEY}` and anything it echoes back —
+    // that header, its own set-cookie — would reach the relay-token holder
+    // (GHSA-9m72-44hg-w32g).
+    const newHeaders = stripSensitiveResponseHeaders(upstream.headers);
     newHeaders.set("X-Routed-By", "bifrost");
     newHeaders.set("X-Relay-Token", token.tokenPrefix + "...");
     if (!wantsStream) {
@@ -321,6 +330,28 @@ export async function POST(request: Request) {
     }
 
     clearTimeout(tid);
+
+    // Normalize non-2xx through parseUpstreamError + buildErrorBody instead of
+    // relaying the sidecar body verbatim — parity with the TS sibling route and
+    // Hard Rule #12 (GHSA-9m72-44hg-w32g).
+    if (!upstream.ok) {
+      const parsed = await parseUpstreamError(upstream, null);
+      const errorBody = buildErrorBody(
+        parsed.statusCode,
+        sanitizeErrorMessage(parsed.message),
+        parsed.responseBody
+      );
+      newHeaders.set("Content-Type", "application/json");
+      if (parsed.retryAfterMs && parsed.retryAfterMs > 0) {
+        newHeaders.set("Retry-After", String(Math.ceil(parsed.retryAfterMs / 1000)));
+      }
+      recordUsage("error", parsed.statusCode);
+      return new Response(JSON.stringify(errorBody), {
+        status: parsed.statusCode,
+        headers: newHeaders,
+      });
+    }
+
     recordUsage(upstream.status < 500 ? "success" : "error", upstream.status);
 
     return new Response(upstream.body, {
diff --git a/src/app/api/v1/relay/chat/completions/route.ts b/src/app/api/v1/relay/chat/completions/route.ts
index fa40d4a009..4e43bb7a13 100644
--- a/src/app/api/v1/relay/chat/completions/route.ts
+++ b/src/app/api/v1/relay/chat/completions/route.ts
@@ -7,6 +7,7 @@
  */
 
 import { CORS_HEADERS, handleCorsOptions } from "@/shared/utils/cors";
+import { stripSensitiveResponseHeaders } from "@omniroute/open-sse/utils/upstreamResponseHeaders";
 import { handleChat } from "@/sse/handlers/chat";
 import { withChatAdmission } from "@/shared/middleware/withChatAdmission";
 import { createInjectionGuard } from "@/middleware/promptInjectionGuard";
@@ -109,7 +110,9 @@ async function forwardToBifrost(
       signal: ac.signal,
     });
 
-    const headers = new Headers(upstream.headers);
+    // Same strip as the bifrost sibling: an echoed upstream credential or
+    // set-cookie must not reach the relay-token holder (GHSA-9m72-44hg-w32g).
+    const headers = stripSensitiveResponseHeaders(upstream.headers);
     headers.set("X-Routed-By", "bifrost");
     headers.set("X-Routing-Backend", "bifrost");
     headers.set("X-Relay-Token", token.tokenPrefix + "...");
diff --git a/stryker.conf.json b/stryker.conf.json
index 96f421f624..27e2825662 100644
--- a/stryker.conf.json
+++ b/stryker.conf.json
@@ -244,6 +244,7 @@
       "tests/unit/embeddings-auth.test.ts",
       "tests/unit/error-classification.test.ts",
       "tests/unit/error-message-sanitization.test.ts",
+      "tests/unit/error-sanitizer-sk-key-qv45.test.ts",
       "tests/unit/error-sensitive-redaction.test.ts",
       "tests/unit/execute-chat-resource-pressure-breaker.test.ts",
       "tests/unit/executor-antigravity.test.ts",
diff --git a/tests/unit/bifrost-relay-response-leak-9m72.test.ts b/tests/unit/bifrost-relay-response-leak-9m72.test.ts
new file mode 100644
index 0000000000..c5affaf655
--- /dev/null
+++ b/tests/unit/bifrost-relay-response-leak-9m72.test.ts
@@ -0,0 +1,103 @@
+/**
+ * GHSA-9m72-44hg-w32g — the standalone bifrost relay route copied ALL upstream
+ * response headers (`new Headers(upstream.headers)`) and returned non-2xx bodies
+ * verbatim, while its TypeScript sibling routed non-2xx through
+ * parseUpstreamError + buildErrorBody + stripStaleEncodingHeaders.
+ *
+ * The relay sends `Authorization: Bearer ${BIFROST_API_KEY}` to the sidecar, so
+ * anything the sidecar (or a further upstream) echoes back — that header, its own
+ * `set-cookie`, an `x-api-key` — reached the relay-token holder untouched.
+ *
+ * Both relay routes copy upstream headers, so the strip is a shared helper used
+ * by both rather than a fix in one and a second copy waiting to drift (the
+ * failure mode of GHSA-v7g9 and GHSA-qv45).
+ *
+ * Run with:
+ *   node --import tsx/esm --test tests/unit/bifrost-relay-response-leak-9m72.test.ts
+ */
+
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+import { readFileSync } from "node:fs";
+import { fileURLToPath } from "node:url";
+
+import { stripSensitiveResponseHeaders } from "../../open-sse/utils/upstreamResponseHeaders.ts";
+
+const read = (rel: string) =>
+  readFileSync(fileURLToPath(new URL(`../../${rel}`, import.meta.url)), "utf8");
+
+const BIFROST_ROUTE = "src/app/api/v1/relay/chat/completions/bifrost/route.ts";
+const TS_ROUTE = "src/app/api/v1/relay/chat/completions/route.ts";
+
+describe("stripSensitiveResponseHeaders", () => {
+  it("drops credentials and cookies the upstream echoed back", () => {
+    const upstream = new Headers([
+      ["authorization", "Bearer sidecar-secret"],
+      ["x-api-key", "op-key"],
+      ["x-goog-api-key", "goog-key"],
+      ["api-key", "azure-key"],
+      ["cookie", "session=abc"],
+      ["set-cookie", "session=abc; HttpOnly"],
+      ["proxy-authorization", "Basic zzz"],
+      ["content-type", "application/json"],
+      ["x-request-id", "keep-me"],
+    ]);
+    const out = stripSensitiveResponseHeaders(upstream);
+    for (const gone of [
+      "authorization",
+      "x-api-key",
+      "x-goog-api-key",
+      "api-key",
+      "cookie",
+      "set-cookie",
+      "proxy-authorization",
+    ]) {
+      assert.equal(out.get(gone), null, `${gone} survived`);
+    }
+    assert.equal(out.get("content-type"), "application/json");
+    assert.equal(out.get("x-request-id"), "keep-me");
+  });
+
+  it("also drops the stale framing headers", () => {
+    const out = stripSensitiveResponseHeaders(
+      new Headers([
+        ["content-encoding", "gzip"],
+        ["content-length", "123"],
+        ["transfer-encoding", "chunked"],
+        ["x-keep", "yes"],
+      ])
+    );
+    assert.equal(out.get("content-encoding"), null);
+    assert.equal(out.get("content-length"), null);
+    assert.equal(out.get("transfer-encoding"), null);
+    assert.equal(out.get("x-keep"), "yes");
+  });
+
+  it("does not mutate the input Headers", () => {
+    const input = new Headers([["authorization", "Bearer x"]]);
+    stripSensitiveResponseHeaders(input);
+    assert.equal(input.get("authorization"), "Bearer x");
+  });
+});
+
+describe("both relay routes use the shared strip (GHSA-9m72-44hg-w32g)", () => {
+  for (const route of [BIFROST_ROUTE, TS_ROUTE]) {
+    it(`${route} strips sensitive upstream response headers`, () => {
+      const src = read(route);
+      assert.ok(
+        src.includes("stripSensitiveResponseHeaders"),
+        `${route} relays upstream headers verbatim — a sidecar-echoed credential reaches the caller`
+      );
+      assert.ok(
+        !/new Headers\(upstream\.headers\)/.test(src),
+        `${route} still copies upstream headers wholesale`
+      );
+    });
+  }
+
+  it("the bifrost route normalizes non-2xx through the error sanitizer", () => {
+    const src = read(BIFROST_ROUTE);
+    assert.ok(src.includes("buildErrorBody"), "bifrost non-2xx must not be relayed verbatim");
+    assert.ok(src.includes("sanitizeErrorMessage"), "bifrost non-2xx must be sanitized (HR#12)");
+  });
+});
diff --git a/tests/unit/error-sanitizer-sk-key-qv45.test.ts b/tests/unit/error-sanitizer-sk-key-qv45.test.ts
new file mode 100644
index 0000000000..b92d5ebbb1
--- /dev/null
+++ b/tests/unit/error-sanitizer-sk-key-qv45.test.ts
@@ -0,0 +1,93 @@
+/**
+ * GHSA-qv45-56jc-4wmj — two copies of one redaction rule, and only one got the
+ * `sk-` pattern.
+ *
+ * `upstreamErrorPassthrough.ts`'s CREDENTIAL_LEAK_RE matches `\bsk-[…]{8,}` and
+ * REFUSES verbatim passthrough when an upstream 4xx echoes a key — correctly
+ * treating it as a leak. The body then falls through to `buildErrorBody` →
+ * `sanitizeErrorMessage` → `redactSensitiveErrorText`, which had no `sk-`
+ * pattern at all. So the layer that recognized the credential handed it to a
+ * layer that did not, and OpenAI-style `Incorrect API key provided: sk-proj-…`
+ * bodies were returned to the caller verbatim.
+ *
+ * The passthrough file's own comment says it "mirrors the vocabulary of
+ * redactSensitiveErrorText" — the mirror had diverged. This suite pins both
+ * directions so it cannot diverge again.
+ *
+ * Run with:
+ *   node --import tsx/esm --test tests/unit/error-sanitizer-sk-key-qv45.test.ts
+ */
+
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import { redactSensitiveErrorText, sanitizeErrorMessage } from "../../open-sse/utils/error.ts";
+
+const LEAKY_BODIES = [
+  "Incorrect API key provided: sk-proj-AbCdEfGhIjKlMnOpQrStUv. You can find your API key at …",
+  "401 Unauthorized: sk-ant-api03-abcdefghijklmnopqrstuvwxyz-1234567890",
+  "invalid key sk_live_51H8xKzAbCdEfGhIjKlMn",
+  "Bad credentials for AIzaSyA1B2C3D4E5F6G7H8I9J0KaLbMcNdOeP",
+  "token rejected: eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIn0.dozjgNryP4J3jVmNHl0w5N_XgL0n3I9PlFUP0THsR8U",
+];
+
+describe("redactSensitiveErrorText — raw credential patterns (GHSA-qv45-56jc-4wmj)", () => {
+  for (const body of LEAKY_BODIES) {
+    it(`redacts the raw credential in: ${body.slice(0, 42)}…`, () => {
+      const out = redactSensitiveErrorText(body);
+      assert.ok(!/\bsk[-_][A-Za-z0-9._-]{8,}/.test(out), `sk- survived: ${out}`);
+      assert.ok(!/\bAIza[A-Za-z0-9_-]{20,}/.test(out), `Google key survived: ${out}`);
+      assert.ok(!/\beyJ[A-Za-z0-9_-]{8,}\.[A-Za-z0-9_-]{8,}\./.test(out), `JWT survived: ${out}`);
+      assert.ok(out.includes("[REDACTED"), `nothing was redacted: ${out}`);
+    });
+  }
+
+  it("redacts through sanitizeErrorMessage, the path buildErrorBody actually uses", () => {
+    const out = sanitizeErrorMessage("Incorrect API key provided: sk-proj-AbCdEfGhIjKlMnOpQr.");
+    assert.ok(!out.includes("sk-proj-AbCdEfGhIjKlMnOpQr"), out);
+  });
+
+  it("keeps the pre-existing redactions working", () => {
+    assert.match(redactSensitiveErrorText("401: Bearer abc123def456"), /Bearer \[REDACTED\]/);
+    assert.match(
+      redactSensitiveErrorText('{"api_key":"secret-value","detail":"bad"}'),
+      /\[REDACTED\]/
+    );
+    assert.match(
+      redactSensitiveErrorText("data:image/png;base64,AAAABBBBCCCC"),
+      /\[REDACTED_DATA_URL\]/
+    );
+  });
+
+  it("does not maul ordinary error prose that merely contains 'sk'", () => {
+    for (const benign of [
+      "Model gpt-5 is not available on this plan",
+      "risk score too high",
+      "task sk failed", // short, no credential shape
+      "Rate limit reached for requests",
+    ]) {
+      assert.equal(redactSensitiveErrorText(benign), benign);
+    }
+  });
+});
+
+describe("the two redaction layers stay in step", () => {
+  it("every credential shape the passthrough layer refuses is also redacted here", async () => {
+    // If passthrough REFUSES a body as leaky, the fallback sanitizer is the only
+    // thing standing between that body and the caller. Anything the first layer
+    // calls a credential, the second must scrub.
+    const { shouldPassthroughUpstreamError } =
+      await import("../../open-sse/utils/upstreamErrorPassthrough.ts");
+    for (const body of LEAKY_BODIES) {
+      const payload = { error: { message: body } };
+      const relayedVerbatim = shouldPassthroughUpstreamError(401, payload);
+      if (relayedVerbatim) continue; // not classified as a leak — nothing to assert
+      const scrubbed = redactSensitiveErrorText(body);
+      assert.notEqual(
+        scrubbed,
+        body,
+        `passthrough refused this body as leaky but the sanitizer left it untouched: ${body}`
+      );
+    }
+  });
+});
diff --git a/tests/unit/search-baseurl-client-override-3f8g.test.ts b/tests/unit/search-baseurl-client-override-3f8g.test.ts
new file mode 100644
index 0000000000..17ada75dce
--- /dev/null
+++ b/tests/unit/search-baseurl-client-override-3f8g.test.ts
@@ -0,0 +1,159 @@
+/**
+ * GHSA-3f8g-pfh9-j687 — a tenant-supplied `provider_options.baseUrl` redirected
+ * the SaaS search builders, so the OPERATOR's search-provider API key was sent
+ * to a tenant-chosen host (query string for google-pse/searchapi, header for
+ * you.com/linkup/nimble/ollama).
+ *
+ * This is the same override the GHSA-j7j4-g9qc-q69c fix hardened — and that fix
+ * only added a block-metadata check, which does nothing here: the attacker
+ * points at their own PUBLIC host and collects the key. The j7j4 regression test
+ * missed it because its fixture was `searxng-search`, the one keyless provider
+ * where redirecting the base URL leaks no credential.
+ *
+ * The two override sources have different trust:
+ *   - `providerSpecificData` comes from the stored provider connection
+ *     (`credentials?.providerSpecificData`, search.ts:1510) — OPERATOR config.
+ *     This is how an operator points at their self-hosted searxng, so it keeps
+ *     working on loopback/LAN under the block-metadata policy.
+ *   - `providerOptions` comes straight off the request body
+ *     (`body.provider_options`, v1/search/route.ts:366) — TENANT input. It is
+ *     refused outright: no provider needs a per-request caller-chosen fetch
+ *     target, and honoring one is credential exfiltration for keyed providers
+ *     and SSRF-with-readback for every provider.
+ *
+ * Run with:
+ *   node --import tsx/esm --test tests/unit/search-baseurl-client-override-3f8g.test.ts
+ */
+
+import { describe, it } from "node:test";
+import assert from "node:assert/strict";
+
+import { resolveSearchBaseUrl } from "../../open-sse/handlers/search.ts";
+import type { SearchProviderConfig } from "../../open-sse/config/searchRegistry.ts";
+import { SEARCH_PROVIDERS } from "../../open-sse/config/searchRegistry.ts";
+
+const base = { query: "test", searchType: "web", maxResults: 5 };
+
+/** Every provider whose builder attaches an operator-held key. */
+const KEYED_PROVIDER_IDS = Object.values(SEARCH_PROVIDERS)
+  .filter((p) => p.authType === "apikey")
+  .map((p) => p.id);
+
+describe("resolveSearchBaseUrl — tenant-supplied baseUrl (GHSA-3f8g-pfh9-j687)", () => {
+  it("covers every keyed provider in the registry, not one hand-picked fixture", () => {
+    // The j7j4 test only exercised searxng. Assert the registry actually has
+    // keyed providers so this suite cannot silently degrade to zero coverage.
+    assert.ok(
+      KEYED_PROVIDER_IDS.length >= 5,
+      `expected keyed providers, got ${KEYED_PROVIDER_IDS.length}`
+    );
+  });
+
+  for (const id of KEYED_PROVIDER_IDS) {
+    it(`refuses a tenant baseUrl for the keyed provider ${id}`, () => {
+      const config = SEARCH_PROVIDERS[id];
+      assert.throws(
+        () =>
+          resolveSearchBaseUrl(config, {
+            ...base,
+            providerOptions: { baseUrl: "https://attacker.example" },
+          }),
+        `${id} honored a tenant baseUrl — the operator key would be sent there`
+      );
+    });
+  }
+
+  it("the opt-in flag is NEVER set on a provider that carries an operator key", () => {
+    // The whole invariant in one assertion: if this ever pairs with authType
+    // "apikey", a caller can redirect the operator's key again.
+    for (const p of Object.values(SEARCH_PROVIDERS)) {
+      if (p.allowClientBaseUrlOverride) {
+        assert.equal(p.authType, "none", `${p.id} opts into a caller baseUrl while holding a key`);
+      }
+    }
+  });
+
+  it("refuses a caller baseUrl for keyless providers that did NOT opt in", () => {
+    for (const id of ["context7", "duckduckgo-free"]) {
+      const config = SEARCH_PROVIDERS[id];
+      if (!config || config.allowClientBaseUrlOverride) continue;
+      assert.throws(
+        () =>
+          resolveSearchBaseUrl(config, {
+            ...base,
+            providerOptions: { baseUrl: "https://attacker.example" },
+          }),
+        `${id} honored a caller baseUrl without opting in`
+      );
+    }
+  });
+
+  it("SearXNG keeps its documented self-hosted caller override, IMDS still blocked", () => {
+    // Opted in: keyless, so no operator credential travels with the request.
+    // Loopback/LAN is the point of a self-hosted instance (search-route.test.ts
+    // covers the route-level flow); cloud metadata stays rejected.
+    const config = SEARCH_PROVIDERS["searxng-search"];
+    assert.equal(config.allowClientBaseUrlOverride, true);
+    assert.equal(
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerOptions: { baseUrl: "http://127.0.0.1:8888/search" },
+      }),
+      "http://127.0.0.1:8888/search"
+    );
+    assert.throws(() =>
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerOptions: { baseUrl: "http://169.254.169.254/latest/meta-data/" },
+      })
+    );
+  });
+
+  it("keeps the operator-configured override working, including loopback/LAN", () => {
+    const config = SEARCH_PROVIDERS["searxng-search"];
+    assert.equal(
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerSpecificData: { baseUrl: "http://127.0.0.1:8888/search" },
+      }),
+      "http://127.0.0.1:8888/search"
+    );
+    assert.equal(
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerSpecificData: { baseUrl: "http://10.0.0.5:8888" },
+      }),
+      "http://10.0.0.5:8888"
+    );
+  });
+
+  it("still blocks cloud metadata from the operator source (j7j4 must not regress)", () => {
+    const config = SEARCH_PROVIDERS["searxng-search"];
+    assert.throws(() =>
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerSpecificData: { baseUrl: "http://169.254.169.254/latest/meta-data/" },
+      })
+    );
+  });
+
+  it("the operator source wins over a tenant one instead of the tenant shadowing it", () => {
+    const config = SEARCH_PROVIDERS["searxng-search"];
+    assert.equal(
+      resolveSearchBaseUrl(config, {
+        ...base,
+        providerOptions: { baseUrl: "https://attacker.example" },
+        providerSpecificData: { baseUrl: "http://127.0.0.1:8888" },
+      }),
+      "http://127.0.0.1:8888"
+    );
+  });
+
+  it("falls back to the catalog baseUrl when neither source supplies one", () => {
+    const config: SearchProviderConfig = {
+      ...SEARCH_PROVIDERS["searxng-search"],
+      baseUrl: "http://localhost:8888/search",
+    };
+    assert.equal(resolveSearchBaseUrl(config, base), "http://localhost:8888/search");
+  });
+});
diff --git a/tests/unit/search-baseurl-ssrf-guard.test.ts b/tests/unit/search-baseurl-ssrf-guard.test.ts
index f42335edd3..5e4e1a6217 100644
--- a/tests/unit/search-baseurl-ssrf-guard.test.ts
+++ b/tests/unit/search-baseurl-ssrf-guard.test.ts
@@ -58,18 +58,26 @@ describe("resolveSearchBaseUrl — SSRF guard on client-controlled baseUrl (GHSA
     });
   }
 
-  it("still allows a self-hosted loopback/LAN override (block-metadata, not public-only)", () => {
+  // CORRECTED for GHSA-3f8g-pfh9-j687. This case originally asserted the
+  // loopback/LAN override via `providerOptions` — i.e. via TENANT input — which
+  // is the SSRF-with-readback half of that advisory. The self-hosted use case
+  // this test was written to protect is operator configuration, and it arrives
+  // on `providerSpecificData` (search.ts reads it from the stored connection's
+  // `credentials?.providerSpecificData`), so that is where it is asserted now.
+  // Tenant-supplied overrides are refused outright — see
+  // search-baseurl-client-override-3f8g.test.ts.
+  it("still allows a self-hosted loopback/LAN override from OPERATOR config", () => {
     assert.equal(
       resolveSearchBaseUrl(config, {
         ...base,
-        providerOptions: { baseUrl: "http://127.0.0.1:9999" },
+        providerSpecificData: { baseUrl: "http://127.0.0.1:9999" },
       }),
       "http://127.0.0.1:9999"
     );
     assert.equal(
       resolveSearchBaseUrl(config, {
         ...base,
-        providerOptions: { baseUrl: "http://10.0.0.5:8080" },
+        providerSpecificData: { baseUrl: "http://10.0.0.5:8080" },
       }),
       "http://10.0.0.5:8080"
     );