Backend identity spoofing via non-canonical header assignment
Published Mar 27, 2026 · Updated Mar 27, 2026
Authentication bypass in Traefik Proxy before 2.11.42, before 3.6.12, or before 3.7.0-ea.3 lets remote authenticated users spoof identities. The BasicAuth and DigestAuth middleware assigns the authenticated username directly to req.Header under the configured literal key instead of replacing its canonical equivalent. Exploitation requires valid credentials and a non-canonical headerField value; a crafted canonical header reaches a trusting backend first and can grant another user’s authorization context.
Summary
What happened
Authentication bypass in Traefik Proxy before 2.11.42, before 3.6.12, or before 3.7.0-ea.3 lets remote authenticated users spoof identities. The BasicAuth and DigestAuth middleware assigns the authenticated username directly to req.Header under the configured literal key instead of replacing its canonical equivalent. Exploitation requires valid credentials and a non-canonical headerField value; a crafted canonical header reaches a trusting backend first and can grant another user’s authorization context.
The record
- CVE
- CVE-2026-33433
- Published
- Mar 27, 2026
- Updated
- Mar 27, 2026
- Vendor
- Traefik Labs
- Product
- Traefik Proxy
- Classifications
- CWE-290, T1190
- Attack vector
- network
- Privileges
- authenticated
Timeline
How it unfolded
- Mar 27, 2026CVE publishedPublication date reported by the CVE source.
- Mar 27, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
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Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.11.42
- Affected versionversion=>= 3.0.0-beta1, < 3.6.11
- Affected versionversion=>= 3.7.0-ea.1, < 3.7.0-ea.3
What conditions does exploitation require?
What is affected?
Published CVSS scores
CVSS describes severity. EPSS estimates exploitation probability.
Attacks
What attackers are doing with it
Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.
Weakness, pattern, technique
Public exploit references
- GHSA-qr99-7898-vr7c authenticated header injection proof of conceptproof of concept · demonstrated
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
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Your stack
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