diff --git a/changelog.d/fixes/generated-relay-header-sanitization.md b/changelog.d/fixes/generated-relay-header-sanitization.md
new file mode 100644
index 0000000000..0dbbdafce2
--- /dev/null
+++ b/changelog.d/fixes/generated-relay-header-sanitization.md
@@ -0,0 +1 @@
+- Harden generated Cloudflare, Vercel, and Deno relays by stripping hop-by-hop, framing, and proxy authentication headers before forwarding requests upstream.
diff --git a/src/app/api/settings/proxy/deno-deploy/route.ts b/src/app/api/settings/proxy/deno-deploy/route.ts
index 9f55dc46e6..0c277e5d62 100644
--- a/src/app/api/settings/proxy/deno-deploy/route.ts
+++ b/src/app/api/settings/proxy/deno-deploy/route.ts
@@ -105,7 +105,11 @@ Deno.serve(async (request) => {
     return new Response(resolved.reason, { status: resolved.status });
   }
   const headers = new Headers(request.headers);
-  ["x-relay-target", "x-relay-path", "x-relay-auth", "host"].forEach(h => headers.delete(h));
+  [
+    "host", "connection", "content-length", "keep-alive", "proxy-connection",
+    "proxy-authenticate", "proxy-authorization", "transfer-encoding", "te", "trailer", "upgrade",
+    "x-relay-target", "x-relay-path", "x-relay-auth",
+  ].forEach(h => headers.delete(h));
   const init = { method: request.method, headers };
   if (request.method !== "GET" && request.method !== "HEAD") {
     init.body = request.body;
diff --git a/src/app/api/settings/proxy/vercel-deploy/route.ts b/src/app/api/settings/proxy/vercel-deploy/route.ts
index fe83e35814..6debb6e7e6 100644
--- a/src/app/api/settings/proxy/vercel-deploy/route.ts
+++ b/src/app/api/settings/proxy/vercel-deploy/route.ts
@@ -53,7 +53,11 @@ export default async function handler(req) {
     return new Response(resolved.reason, { status: resolved.status });
   }
   const headers = new Headers(req.headers);
-  ["x-relay-target", "x-relay-path", "x-relay-auth", "host"].forEach(h => headers.delete(h));
+  [
+    "host", "connection", "content-length", "keep-alive", "proxy-connection",
+    "proxy-authenticate", "proxy-authorization", "transfer-encoding", "te", "trailer", "upgrade",
+    "x-relay-target", "x-relay-path", "x-relay-auth",
+  ].forEach(h => headers.delete(h));
   const upstream = await fetch(resolved.url, {
     method: req.method,
     headers,
diff --git a/src/lib/proxyRelay/cloudflareWorkerScript.ts b/src/lib/proxyRelay/cloudflareWorkerScript.ts
index c25c602122..1e22766f96 100644
--- a/src/lib/proxyRelay/cloudflareWorkerScript.ts
+++ b/src/lib/proxyRelay/cloudflareWorkerScript.ts
@@ -109,7 +109,11 @@ async function handleRelay(request) {
   }
   const relayPath = request.headers.get("x-relay-path") || "/";
   const headers = new Headers(request.headers);
-  ["x-relay-target", "x-relay-path", "x-relay-auth", "host"].forEach((h) => headers.delete(h));
+  [
+    "host", "connection", "content-length", "keep-alive", "proxy-connection",
+    "proxy-authenticate", "proxy-authorization", "transfer-encoding", "te", "trailer", "upgrade",
+    "x-relay-target", "x-relay-path", "x-relay-auth",
+  ].forEach((h) => headers.delete(h));
   const init = {
     method: request.method,
     headers,
diff --git a/tests/unit/generated-relay-header-denylist.test.ts b/tests/unit/generated-relay-header-denylist.test.ts
new file mode 100644
index 0000000000..0b91f6bc33
--- /dev/null
+++ b/tests/unit/generated-relay-header-denylist.test.ts
@@ -0,0 +1,45 @@
+import assert from "node:assert/strict";
+import { describe, it } from "node:test";
+
+import { __buildRelayWorkerForTest } from "../../src/app/api/settings/proxy/deno-deploy/route";
+import { __buildRelayFunctionForTest } from "../../src/app/api/settings/proxy/vercel-deploy/route";
+import { buildCloudflareWorkerScript } from "../../src/lib/proxyRelay/cloudflareWorkerScript";
+
+const FORBIDDEN_RELAY_HEADERS = [
+  "host",
+  "connection",
+  "content-length",
+  "keep-alive",
+  "proxy-connection",
+  "proxy-authenticate",
+  "proxy-authorization",
+  "transfer-encoding",
+  "te",
+  "trailer",
+  "upgrade",
+  "x-relay-target",
+  "x-relay-path",
+  "x-relay-auth",
+];
+
+const relays = {
+  Cloudflare: buildCloudflareWorkerScript("relay-secret"),
+  Vercel: __buildRelayFunctionForTest("relay-secret"),
+  Deno: __buildRelayWorkerForTest("relay-secret"),
+};
+
+describe("generated relay request header sanitization", () => {
+  for (const [runtime, source] of Object.entries(relays)) {
+    it(`${runtime} strips relay controls, framing, and hop-by-hop headers`, () => {
+      const deletionBlock = source.match(
+        /const headers = new Headers\([^;]+\);\s*\[([\s\S]*?)\]\.forEach\(\(?h\)?\s*=>\s*headers\.delete\(h\)\);/
+      );
+      assert.ok(deletionBlock, `${runtime} generated source must sanitize forwarded headers`);
+
+      const deletedHeaders = [...deletionBlock[1].matchAll(/["']([^"']+)["']/g)].map(
+        (match) => match[1]
+      );
+      assert.deepEqual(deletedHeaders, FORBIDDEN_RELAY_HEADERS);
+    });
+  }
+});