CVE-2026-33433

Name: CVE-2026-33433
Creator: NVD / NIST
Published: 2026-03-27T15:16:54.98+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 5.1/10EPSS 0.45%

Last modified Jun 17, 2026

CVE-2026-33433 is a medium-severity vulnerability rated 5.1/10 on the CVSS scale. Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. EPSS estimates a 0.45% chance of exploitation in the next 30 days.

Description

Traefik is an HTTP reverse proxy and load balancer. Prior to versions 2.11.42, 3.6.11, and 3.7.0-ea.3, when `headerField` is configured with a non-canonical HTTP header name (e.g., `x-auth-user` instead of `X-Auth-User`), an authenticated attacker can inject their own canonical version of that header to impersonate any identity to the backend. The backend receives two header entries — the attacker-injected canonical one is read first, overriding Traefik's non-canonical write. Versions 2.11.42, 3.6.11, and 3.7.0-ea.3 patch the issue.

Metrics

CVSS 3.1

8.8/10

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

CVSS 4.0

5.1/10

CVSS:4.0/AV:N/AC:H/AT:P/PR:H/UI:N/VC:N/VI:N/VA:N/SC:H/SI:H/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

EPSS Probability

0.45%

35.9th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-290

Affected Software

Vendor	Product	Versions	Update
Traefik	Traefik	< 2.11.42	—
Traefik	Traefik	>= 3.0.0, < 3.6.12	—
Traefik	Traefik	3.7.0	Ea1

References

https://github.com/traefik/traefik/releases/tag/v2.11.42Product, Release Notes
https://github.com/traefik/traefik/releases/tag/v3.6.11Product, Release Notes
https://github.com/traefik/traefik/releases/tag/v3.7.0-ea.3Product, Release Notes
https://github.com/traefik/traefik/security/advisories/GHSA-qr99-7898-vr7cExploit, Patch, Vendor Advisory

Timeline

Published: Mar 27, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2026-33433?

How severe is CVE-2026-33433?

CVE-2026-33433 has a CVSS score of 5.1/10 (MEDIUM severity). The EPSS model estimates a 0.45% probability of exploitation in the next 30 days.

How do I fix CVE-2026-33433?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2026-33433?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST