Your RSA-2048 keys break in 2030. Find every one of them before attackers do.
🐹 Go

GHSA-6x2q-h3cr-8j2h

LOW

GHSA-6x2q-h3cr-8j2h is a low-severity (CVSS 3.7) vulnerability in github.com/traefik/traefik/v3. O3 Security confirms whether GHSA-6x2q-h3cr-8j2h is actually reachable in your code before you act, and blocks exploitation at runtime until you patch.

Traefik: A timing side-channel vulnerability allows for valid username enumeration via BasicAuth middleware

Also known asCVE-2026-41263GO-2026-5195
Published
Apr 24, 2026
Updated
Jun 25, 2026
Affected
4 pkgs
Patched
3 / 4
Exploits
None indexed

Blast Radius

4 pkgs affected
🐹github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v2🐹github.com/traefik/traefik

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Summary

There is a timing side-channel vulnerability in Traefik's BasicAuth middleware that allows an attacker to enumerate valid usernames through response-time differences.

The variable intended to hold a constant-time fallback secret always resolves to an empty string, causing the constant-time comparison to short-circuit in microseconds rather than performing a full bcrypt evaluation. This restores the original timing oracle and makes it possible to distinguish existing users from non-existing ones by measuring authentication response times.

Patches

For more information

If there are any questions or comments about this advisory, please open an issue.

<details> <summary>Original Description</summary>

BasicAuth Timing Regression: CVE-2026-32595 Fix Is a No-Op Due to Map Key/Value Confusion

TL;DR

The patch for CVE-2026-32595 is a no-op. Line 49 of basic_auth.go has a map key/value confusion that makes notFoundSecret always "". The "constant time" fallback calls goauth.CheckSecret(password, ""), which fast-fails in ~1us instead of running bcrypt (~60ms).

Evidence (HEAD 786f7192e, 2026-04-09)

Black-box PoC against live traefik binary on port 28080:

bucketnmedianmin
existing user (wrong pw)24062.85 ms57.54 ms
nonexistent user (wrong pw)4000.48 ms0.35 ms

Median ratio: 130.4x. Classification: 8/8 correct.

Go in-tree test: goauth.CheckSecret direct ratio 12,746x.

Root cause (4-step trace)

  1. basic_auth.go:49: users[slices.Collect(maps.Values(users))[0]] -- looks up a hash as a username key, returns "".
  2. basic_auth.go:119-120: calls goauth.CheckSecret(password, "").
  3. go-http-auth/basic.go:87: empty string matches no prefix, falls to default compareMD5HashAndPassword.
  4. basic.go:107-109: bytes.SplitN("", "$", 4) returns length 1, function returns instantly.

Files

  • poc/exploit.py -- black-box Python timing oracle
  • poc/basic_auth_timing_regression_test.go -- Go in-tree test
  • poc/traefik.yml + poc/dynamic.yml -- traefik config
  • poc/live_http_poc_output_head.txt -- verbatim PoC output on HEAD

Koda Reef

</details>

Affected Packages

4 total 3 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/traefik/traefik/v3≥ 3.7.0-ea.1&&< 3.7.0-rc.23.7.0-rc.2
🐹Gogithub.com/traefik/traefik/v3≥ 3.0.0-beta1&&< 3.6.143.6.14
🐹Gogithub.com/traefik/traefik/v2all versions2.11.43
🐹Gogithub.com/traefik/traefikall versionsNo fix

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/traefik/traefik/v3. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

  2. Fix

    Update github.com/traefik/traefik/v3 to 3.7.0-rc.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-6x2q-h3cr-8j2h is resolved across your whole dependency graph.

  3. Workarounds

    If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

  4. How O3 protects you

    O3 pinpoints whether GHSA-6x2q-h3cr-8j2h is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to GHSA-6x2q-h3cr-8j2h. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

## Summary There is a timing side-channel vulnerability in Traefik's BasicAuth middleware that allows an attacker to enumerate valid usernames through response-time differences. The variable intended to hold a constant-time fallback secret always resolves to an empty string, causing the constant-time comparison to short-circuit in microseconds rather than performing a full bcrypt evaluation. This restores the original timing oracle and makes it possible to distinguish existing users from non-existing ones by measuring authentication response times. ## Patches - https://github.com/traefik/t
O3 Security · Impact-Aware SCA

Is GHSA-6x2q-h3cr-8j2h in your dependencies?

O3 detects GHSA-6x2q-h3cr-8j2h across Go dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works