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CVE-2026-33433

Traefik authentication bypass

8.8 HIGHPublic exploitEPSS 0.56%
  1. Published27 Mar 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredLow
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityHigh
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Affected products

Traefik≥ 3.0.0 < 3.6.12 · < 2.11.42 · 3.7.0

Remediation

Fixed in
Traefik≥ 3.6.12

References

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Frequently asked

Is CVE-2026-33433 being actively exploited?

CVE-2026-33433 is not in the CISA KEV catalog. A public exploit reference exists, so treat it as exploitable. Its EPSS exploit probability is 0.56%.

How severe is CVE-2026-33433?

CVE-2026-33433 has a CVSS 3.1 base score of 8.8, rated high. EPSS estimates a 0.56% probability of exploitation.

Which products are affected by CVE-2026-33433?

Affected products include Traefik.

How do I fix CVE-2026-33433?

Upgrade affected software to a fixed version, for example Traefik 3.6.12 or later, then confirm no affected versions remain in your inventory.

How Secuno handles this

Secuno correlates vulnerabilities like CVE-2026-33433 against the real software inventory on every managed device, as each hourly inventory arrives. Rather than a static severity, each match is scored in context: exploit availability, EPSS, the asset's exposure, and business criticality decide where it lands in the queue. If an affected version is present anywhere across your portfolio, it surfaces automatically with a prioritised remediation path.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.