GHSA-6x2q-h3cr-8j2h — v3
LOWGHSA-6x2q-h3cr-8j2h is a low-severity (CVSS 3.7) CWE-208 vulnerability in github.com/traefik/traefik/v3. A fix is available for github.com/traefik/traefik/v3 — see the affected versions and patch details below.
Traefik: A timing side-channel vulnerability allows for valid username enumeration via BasicAuth middleware
Exploitation Status
No confirmed exploitation observed yet
- CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.
Exploitation and automatability from CISA’s SSVC triage for GHSA-6x2q-h3cr-8j2h.
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
GHSA-6x2q-h3cr-8j2h plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 379,145 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v3🐹github.com/traefik/traefik/v2🐹github.com/traefik/traefikReal-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
- https://github.com/traefik/traefik/releases/tag/v2.11.43
- https://github.com/traefik/traefik/releases/tag/v3.6.14
- https://github.com/traefik/traefik/releases/tag/v3.7.0-rc.2
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:
| bucket | n | median | min |
|---|---|---|---|
| existing user (wrong pw) | 240 | 62.85 ms | 57.54 ms |
| nonexistent user (wrong pw) | 400 | 0.48 ms | 0.35 ms |
Median ratio: 130.4x. Classification: 8/8 correct.
Go in-tree test: goauth.CheckSecret direct ratio 12,746x.
Root cause (4-step trace)
basic_auth.go:49:users[slices.Collect(maps.Values(users))[0]]-- looks up a hash as a username key, returns"".basic_auth.go:119-120: callsgoauth.CheckSecret(password, "").go-http-auth/basic.go:87: empty string matches no prefix, falls to defaultcompareMD5HashAndPassword.basic.go:107-109:bytes.SplitN("", "$", 4)returns length 1, function returns instantly.
Files
poc/exploit.py-- black-box Python timing oraclepoc/basic_auth_timing_regression_test.go-- Go in-tree testpoc/traefik.yml+poc/dynamic.yml-- traefik configpoc/live_http_poc_output_head.txt-- verbatim PoC output on HEAD
Koda Reef
</details>Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/traefik/traefik/v3 | ≥ 3.7.0-ea.1&&< 3.7.0-rc.2 | 3.7.0-rc.2go get github.com/traefik/traefik/v3@v3.7.0-rc.2 |
| 🐹Go | github.com/traefik/traefik/v3 | ≥ 3.0.0-beta1&&< 3.6.14 | 3.6.14go get github.com/traefik/traefik/v3@v3.6.14 |
| 🐹Go | github.com/traefik/traefik/v2 | all versions | 2.11.43go get github.com/traefik/traefik/v2@v2.11.43 |
| 🐹Go | github.com/traefik/traefik | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/traefik/traefik/v3, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
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.
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.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like GHSA-6x2q-h3cr-8j2h can be triaged on real exposure rather than presence alone.
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
Is GHSA-6x2q-h3cr-8j2h in your dependencies?
O3 Security finds GHSA-6x2q-h3cr-8j2h across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.