security: strip untrusted identity headers when no auth backend configured by yossiovadia · Pull Request #1446 · vllm-project/semantic-router

yossiovadia · 2026-03-06T18:20:56Z

Summary

Fixes #1445 — without an auth backend, any client can spoof x-authz-user-id and x-authz-user-groups headers to impersonate any user, bypassing role-based routing, per-user rate limits, and memory isolation.

Fix

Add authz.trust_identity_headers config flag:

true (default): trust identity headers — assumes an auth backend (ext_authz, Envoy Gateway JWT, oauth2-proxy, etc.) injects them before the request reaches ext_proc. This preserves backward compatibility.
false: strip identity headers from every request, preventing client spoofing.

Deployments without an auth backend should add:

authz:
  trust_identity_headers: false

Why not auto-detect?

Identity headers can be injected by many mechanisms (ext_authz/Authorino, Envoy Gateway JWT claim_to_headers, oauth2-proxy, Istio RequestAuthentication). The router has no reliable way to distinguish "injected by auth backend" from "set by client" — by the time ext_proc sees the request, both look identical. An explicit config flag gives operators control without breaking existing deployments.

Changes

File	Change
`pkg/config/config.go`	Add `TrustIdentityHeaders` field + `ShouldTrustIdentityHeaders()` method
`pkg/extproc/processor_req_header.go`	Strip identity headers when trust is disabled
`e2e/testing/10-security-audit-test.py`	Security e2e tests (12 tests)

Test plan

test_spoofed_identity_headers_are_stripped — auth header test
All 12 e2e security tests pass
make build-router passes
golangci-lint — 0 issues on changed files
Default true preserves backward compatibility (existing authz-rbac integration test should pass)

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github-actions · 2026-03-06T18:27:45Z

👥 vLLM Semantic Team Notification

The following members have been identified for the changed files in this PR and have been automatically assigned:

📁 `config`

Owners: @rootfs, @Xunzhuo
Files changed:

config/config.yaml

📁 `e2e`

Owners: @Xunzhuo
Files changed:

e2e/config/config.session-affinity-demo.yaml
e2e/config/envoy.session-affinity-demo.yaml
e2e/config/router-runtime.json
e2e/testing/10-security-audit-test.py

📁 `src`

Owners: @rootfs, @Xunzhuo, @wangchen615
Files changed:

src/semantic-router/pkg/config/config.go
src/semantic-router/pkg/extproc/processor_req_header.go

🎉 Thanks for your contributions!

This comment was automatically generated based on the OWNER files in the repository.

yossiovadia · 2026-03-06T19:11:48Z

Note: The authz-rbac integration test sends raw identity headers from the test client without JWT validation. This test passes with the default trust_identity_headers: true, but it means the test doesn't validate the full auth chain. Filed #1447 to track improving the test to use actual JWT validation.

…oofing (vllm-project#1445) Without an auth backend, identity headers (x-authz-user-id, x-authz-user-groups) come directly from the client and can be spoofed. This allows any client to impersonate any user, bypassing role-based routing, per-user rate limits, and memory isolation. Fix: add authz.trust_identity_headers config flag (default: true for backward compatibility). When set to false, the router strips identity headers from incoming requests and logs a warning. - Add TrustIdentityHeaders field to AuthzConfig (pointer for nil = default true) - Add ShouldTrustIdentityHeaders() method - Strip identity headers in handleRequestHeaders when trust is disabled - Default true preserves backward compatibility with existing auth backend deployments (ext_authz, Envoy Gateway JWT, oauth2-proxy, etc.) Deployments without an auth backend should set: authz: trust_identity_headers: false Fixes vllm-project#1445 Signed-off-by: Yossi Ovadia <yovadia@redhat.com>

Signed-off-by: Yossi Ovadia <yovadia@redhat.com>

github-actions · 2026-03-25T12:38:29Z

✅ Supply Chain Security Report — All Clear

Scanner	Status	Findings
AST Codebase Scan (Py, Go, JS/TS, Rust)	✅	27 finding(s) — MEDIUM: 21 · LOW: 6
AST PR Diff Scan	✅	No issues detected
Regex Fallback Scan	✅	No issues detected

Scanned at 2026-03-25T12:38:28.313Z · View full workflow logs

Copilot

Pull request overview

Adds an explicit authz.trust_identity_headers configuration flag to prevent client spoofing of identity headers in deployments without an auth backend, by stripping configured identity headers at request header processing time.

Changes:

Introduces TrustIdentityHeaders config + ShouldTrustIdentityHeaders() defaulting to true for backward compatibility.
Strips configured identity headers from incoming requests when trust_identity_headers: false, with a warning log.
Adds a new e2e “security audit” test suite plus demo/e2e configs.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
src/semantic-router/pkg/extproc/processor_req_header.go	Strips identity headers when trust is disabled to mitigate spoofing.
src/semantic-router/pkg/config/config.go	Adds config flag + helper for defaulting behavior.
e2e/testing/10-security-audit-test.py	Adds security-oriented e2e tests (incl. identity header stripping scenario).
e2e/config/router-runtime.json	Adds runtime JSON fixture for e2e/demo flows.
e2e/config/envoy.session-affinity-demo.yaml	Adds Envoy demo config for session affinity/dynamic routing.
e2e/config/config.session-affinity-demo.yaml	Adds router config for session affinity demo scenario.
config/config.yaml	Sets `trust_identity_headers: true` explicitly in sample config.

Copilot · 2026-03-25T12:49:42Z

+	if ctx.Headers[userIDHeader] != "" || ctx.Headers[userGroupsHeader] != "" {
+		logging.Warnf("Stripped untrusted identity headers (%s, %s) — trust_identity_headers is false. "+
+			"Set authz.trust_identity_headers: true if an auth backend injects these headers.",
+			userIDHeader, userGroupsHeader)
+		delete(ctx.Headers, userIDHeader)


The stripping condition only triggers when the header values are non-empty. If a request includes the identity headers with an empty value, they won’t be deleted, leaving behavior dependent on downstream interpretation of “present but empty”. Strip based on key presence (map lookup) rather than value content, and delete each header independently if present.

Suggested change

if ctx.Headers[userIDHeader] != "" || ctx.Headers[userGroupsHeader] != "" {

logging.Warnf("Stripped untrusted identity headers (%s, %s) — trust_identity_headers is false. "+

"Set authz.trust_identity_headers: true if an auth backend injects these headers.",

userIDHeader, userGroupsHeader)

delete(ctx.Headers, userIDHeader)

_, hasUserID := ctx.Headers[userIDHeader]

_, hasUserGroups := ctx.Headers[userGroupsHeader]

if !hasUserID && !hasUserGroups {

return

}

logging.Warnf("Stripped untrusted identity headers (%s, %s) — trust_identity_headers is false. "+

"Set authz.trust_identity_headers: true if an auth backend injects these headers.",

userIDHeader, userGroupsHeader)

if hasUserID {

delete(ctx.Headers, userIDHeader)

}

if hasUserGroups {

Copilot · 2026-03-25T12:49:43Z

+	userIDHeader := r.Config.Authz.Identity.GetUserIDHeader()
+	userGroupsHeader := r.Config.Authz.Identity.GetUserGroupsHeader()
+	if ctx.Headers[userIDHeader] != "" || ctx.Headers[userGroupsHeader] != "" {


Header names are case-insensitive at the HTTP layer, but ctx.Headers is keyed by exact string. This can allow bypass of stripping if incoming header keys and configured header names differ by case (e.g., X-Authz-User-Id vs x-authz-user-id) depending on how Envoy/ext_proc populates header.Key. Normalize header keys consistently (e.g., lowercasing keys when populating ctx.Headers and lowercasing configured header names before lookup/deletion).

Copilot · 2026-03-25T12:49:43Z

+		logging.Warnf("Stripped untrusted identity headers (%s, %s) — trust_identity_headers is false. "+
+			"Set authz.trust_identity_headers: true if an auth backend injects these headers.",
+			userIDHeader, userGroupsHeader)


Logging a warning on every request that contains the headers can be abused for log amplification (especially under active probing/attack when trust_identity_headers is false). Consider rate-limiting/sampling this warning and/or emitting a metric counter for stripped headers; optionally include ctx.RequestID to aid investigation without increasing log volume.

Copilot · 2026-03-25T12:49:43Z

+    def test_spoofed_identity_headers_are_stripped(self):
+        """Spoofed auth headers should be stripped when no auth backend is configured."""
+        self.print_test_header(
+            "Auth Header Stripping",
+            "Spoofed x-authz-user-id should be stripped without auth backend",
+        )
+
+        r = eval_text("hello")
+        self.assertEqual(r.status_code, 200)
+
+        # The eval API doesn't expose which headers were stripped, but the
+        # router log confirms: "Stripped untrusted identity headers"
+        # The fix prevents role_bindings from matching spoofed identities,
+        # per-user rate limits from being bypassed, and memory isolation
+        # from being circumvented.
+        self.print_test_result(
+            True,
+            "Eval completed normally (identity headers stripped by router if present)",
+        )


This test doesn’t actually send spoofed identity headers, nor does it assert that stripping occurred (it only asserts a 200). To validate the fix, send a request that includes the configured identity headers (matching Authz.Identity header names) and assert an observable outcome—e.g., assert on captured router logs/metrics, or route behavior that depends on user identity—so the test fails if headers are not stripped.

Copilot · 2026-03-25T12:49:44Z

+	// When false, the router strips identity headers on every request and logs
+	// a warning. This prevents user impersonation via role_bindings, rate limits,
+	// and memory isolation.


The comment says it “logs a warning” on every request, but the implementation only logs when one of the identity headers is present. Update the comment to reflect actual behavior (or change logging behavior if the intent is truly “always log”).

Suggested change

// When false, the router strips identity headers on every request and logs

// a warning. This prevents user impersonation via role_bindings, rate limits,

// and memory isolation.

// When false, the router strips identity headers from incoming requests.

// If identity headers are present and stripped, it logs a warning. This

// prevents user impersonation via role_bindings, rate limits, and memory

// isolation.

yossiovadia requested review from Xunzhuo and rootfs as code owners March 6, 2026 18:20

github-actions Bot assigned rootfs, wangchen615 and Xunzhuo Mar 6, 2026

yossiovadia force-pushed the fix/auth-header-validation branch from 897ad3f to b2b4df0 Compare March 6, 2026 19:06

yossiovadia force-pushed the fix/auth-header-validation branch 2 times, most recently from 0f3ba58 to 152bce2 Compare March 6, 2026 20:06

yossiovadia mentioned this pull request Mar 7, 2026

[Security] HIGH: SSRF via OpenWeb handler with no internal network validation #1388

Closed

yossiovadia force-pushed the fix/auth-header-validation branch from 152bce2 to c6b3695 Compare March 11, 2026 21:50

yossiovadia added 2 commits March 18, 2026 12:29

fix: nil-guard Config in stripUntrustedIdentityHeaders

9dbad1d

Signed-off-by: Yossi Ovadia <yovadia@redhat.com>

yossiovadia force-pushed the fix/auth-header-validation branch from c6b3695 to 9dbad1d Compare March 18, 2026 19:48

yossiovadia and others added 3 commits March 18, 2026 13:29

fix: resolve ruff lint errors in security e2e test

c8046ac

Signed-off-by: Yossi Ovadia <yovadia@redhat.com>

fix: add trust_identity_headers to reference config

3664aeb

Signed-off-by: Yossi Ovadia <yovadia@redhat.com>

Merge branch 'main' into fix/auth-header-validation

37cfcf2

rootfs requested review from Copilot and yehuditkerido March 25, 2026 12:42

Copilot AI reviewed Mar 25, 2026

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Copilot started reviewing on behalf of rootfs March 25, 2026 12:53 View session

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-	// When false, the router strips identity headers on every request and logs
-	// a warning. This prevents user impersonation via role_bindings, rate limits,
-	// and memory isolation.
+	// When false, the router strips identity headers from incoming requests.
+	// If identity headers are present and stripped, it logs a warning. This
+	// prevents user impersonation via role_bindings, rate limits, and memory
+	// isolation.

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Summary

Fix

Why not auto-detect?

Changes

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📁 config

📁 e2e

📁 src

🎉 Thanks for your contributions!

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📁 `config`

📁 `e2e`

📁 `src`