---
id: "bug-1950"
status: "fixed"
status_updated: "2026-10-10"
status_note: ""
component: "apiserver"
severity: "security"
timestamp: "2026-10-10T08:15:11Z"
last_seen: "2026-10-10T08:15:11Z"
occurrences: 1
files: ["src/frontend/apiserver/middleware/validatehandler.go"]
tags: ["apiserver", "security", "jwt"]
related: []
fix_commits: ["42dd1e7a"]
gitea_issue: 381
gitea_synced_status: "fixed"
gitea_synced_hash: "edb7a297a683"
---

# bug-1950: apiserver JWT validation does not pin the signing algorithm

## Description
**Observed:** (source reading, `.kiro/reviews/project-gap-review-2026-10-10.md` (P0); to be confirmed by a failing test before the fix)
The middleware's parse callback returns the key without checking `token.Method` (`middleware/validatehandler.go:102-104`), unlike the other parse path (`controllers/auth.go:186`).

**Expected:** Only the configured HMAC algorithm is accepted.
**Impact:** Security hardening: algorithm-confusion class of attacks is not ruled out.
**Found by:** review: `.kiro/reviews/project-gap-review-2026-10-10.md` (P0)
## Environment
- OS: no /etc/os-release; Docker container; NixOS kernel; kernel Linux 6.18.33 x86_64
- libc: glibc 2.42-47 (interpreter /nix/store/wb6rhpznjfczwlwx23zmdrrw74bayxw4-glibc-2.42-47/lib/ld-linux-x86-64.so.2)
- Toolchain: gcc (GCC) 15.2.0, meson 1.9.1
- Build: asan (xce.build)
- Code: scheduler-framework @ 94472ee3-dirty
- Deployment: any (found by source reading; the failing test that confirms it is named in Verification)

## Reproduction
1. Present a token signed with another algorithm family; validation does not reject it on the algorithm.
- Frequency: deterministic (by code reading; confirmed by the RED test of the fix)
- Evidence: the code sites quoted in Description; no logs kept.
## Root cause
`isValidToken()` (`middleware/validatehandler.go`) never checked `token.Method`; `GetUsernameFromToken` accepted any HMAC variant.

## Fix
`controllers/auth.go`: `JWTSigningMethod` (HS256), `JWTKeyFunc`, `JWTValidMethods()`; both parse paths use them.

## Verification
- Test: `TestIsValidToken_PinsSigningAlgorithm` (`middleware/validatehandler_test.go`): RED `isValidToken(HS384) = true, want false`; `TestGetUsernameFromToken_PinsSigningAlgorithm`: RED; GREEN after.
- Suites: `xce-build.sh all asan xce.build --incremental` on the merged branch, 2026-10-10: all C suites Ok 155 / Fail 0, frontend Go unit tests ok, xceadmin tests ok; apiserver `CGO_ENABLED=0 go test ./...` (incl. middleware, router, cmd) ok
- Live: n/a: unit/fixture-level verification only; no live deployment was run (follow-up)

## References
- Fix commit: `42dd1e7a` (on `scheduler-framework`; worker-branch original in the merge)
- Review: `.kiro/reviews/project-gap-review-2026-10-10.md`