CVE-2026-88011

Traefik is an open source HTTP reverse proxy and load balancer. Prior to 2.11.56, and from 3.0.0 until 3.7.12, a client-supplied dot-form header such as X.Authenticated.User survives ForwardAuth replacement and underscoreHeadersStrategy because Go treats it as distinct from X-Authenticated-User while normalization-prone CGI, WSGI, PHP, and NGINX backends collapse both names. A backend can consequently consume the client value instead of the identity Traefik asserted, allowing identity spoofing for any header managed by Traefik. The aliasHeadersStrategy protection is disabled by default and must be configured as delete or reject. The mitigation is available in 2.11.56 and 3.7.12.

What this means for your business

It affects Traefik. It matters if your company, or a supplier that handles your data, runs it.
An attacker can use it remotely, over a network, with an ordinary user login, and without anyone at your company clicking anything.
FIRST's prediction model gives it a 0.2% chance of attack attempts being seen in the next 30 days, ranking above 15% of all known flaws.

What to do

1Check whether your company or your suppliers run Traefik, and which version. The affected versions are listed further down this page.
2If you do, apply the vendor's fix. A patch or vendor advisory has been published.

Not sure if your company is exposed?

Fastnexa’s certified penetration testers can check whether attackers could use this flaw, or others like it, against your websites, apps and network. The full test is free for our first 10 founding clients until 31 December 2026.

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Scoring

CVSS: 8.1 (v3.1)
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
CVSS v4: 5.3
Weakness: CWE-290
Assigned by: security-advisories@github.com

Dates

Published: 2026-09-10
Last modified: 2026-09-15
Sources: NVD

Affected products

Traefik Traefik- 2.11.56, 3.0.0 - 3.7.12

As listed in the NVD configuration data. Not a statement about your estate.