traefik: Authentication Bypass by Spoofing
CVE-2026-33433 is a high-severity authentication bypass by spoofing vulnerability in traefik, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited remotely over the network by an attacker with a low-privileged account, without any action from a user. Affected traefik versions: < 2.11.42; >= 3.0.0-beta1, < 3.6.11; >= 3.7.0-ea.1, < 3.7.0-ea.3. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.5% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Check which version of traefik you run against the affected versions below, and install the vendor's latest release.
- Read the advisory on github.com for workarounds and exact fixed builds.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Traefik | traefik | < 2.11.42; >= 3.0.0-beta1, < 3.6.11; >= 3.7.0-ea.1, < 3.7.0-ea.3 | Not stated |
| Red Hat | Red Hat OpenShift Dev Spaces 3.27 | Not specified in the record | Not stated |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- NetworkCan be exploited remotely over a network, including the internet.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- HighData or code can be modified at will.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 4.0 | 5.1 | Medium | CNA (github.com) |
| CVSS 3.1 | 8.8 | High | NVD |
| CVSS 3.1 | 7.7 | High | CNA |
Official 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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Authentication Bypass by Spoofing
This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks.
More Authentication Bypass by Spoofing vulnerabilities (CWE-290)
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Advisories
Patches and release notes
- github.com/traefik/traefik/releases/tag/v2.11.42Product, Release Notes
- github.com/traefik/traefik/releases/tag/v3.6.11Product, Release Notes
- github.com/traefik/traefik/releases/tag/v3.7.0-ea.3Product, Release Notes
Other references
Other vulnerabilities in traefik
- 8.7 High severity
- 8.7 High severity
- 9.3 Critical severity
- 8.7 High severity
- 8.7 High severity
- 8.7 High severity
Recent Authentication Bypass by Spoofing vulnerabilities
- 7.5 High severity
- 9.8 Critical severity
- 7.5 High severity
- 9.8 Critical severity
- 9.1 Critical severity
- 7.5 High severity
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