CVE-2026-41263

Description

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, 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. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2.

CVSS v3.1 Score

3.7

LOW

CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS — Exploit Prediction

0.0002

Probability of exploitation

0.06%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-208 CWE-208

Affected Products

Vendor	Product	Versions
traefik	traefik	< 2.11.43
traefik	traefik	3.0.0 — 3.6.14
traefik	traefik	All
traefik	traefik	All
traefik	traefik	All
traefik	traefik	All

References

Advisories & Patches

https://github.com/traefik/traefik/security/advisories/GHSA-6x2q-h3cr-8j2h

Other References

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

Frequently Asked Questions

What is CVE-2026-41263? +

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.43, 3.6.14, and 3.7.0-rc.2, 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. This issue has been patched in versions 2.11.43, 3.6.14, and 3.7.0-rc.2. It has a CVSS v3.1 base score of 3.7 (LOW).

How severe is CVE-2026-41263? +

CVE-2026-41263 has a CVSS v3.1 score of 3.7 out of 10, rated LOW. This is a low-severity vulnerability with limited impact. The EPSS score is 0.0002, placing it in the 0th percentile for exploitation probability.

What products are affected by CVE-2026-41263? +

CVE-2026-41263 affects products from traefik, specifically: traefik. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2026-41263? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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