Unauthenticated route access via forwarded-header aliases
Published Apr 30, 2026 · Updated Apr 30, 2026
Authentication bypass in Traefik Proxy allows remote attackers to access protected routes through spoofed forwarded-header aliases. ForwardAuth and snippet-based authentication copy client headers into pre-authentication requests after sanitizing only canonical dashed names, leaving underscore aliases intact for backends that normalize both forms. The route must use affected middleware with a backend whose trust decision depends on normalized forwarded headers; no credentials or user interaction are required.
Summary
What happened
Authentication bypass in Traefik Proxy allows remote attackers to access protected routes through spoofed forwarded-header aliases. ForwardAuth and snippet-based authentication copy client headers into pre-authentication requests after sanitizing only canonical dashed names, leaving underscore aliases intact for backends that normalize both forms. The route must use affected middleware with a backend whose trust decision depends on normalized forwarded headers; no credentials or user interaction are required.
The record
- CVE
- CVE-2026-39858
- Published
- Apr 30, 2026
- Updated
- Apr 30, 2026
- Vendor
- Traefik Labs
- Product
- Traefik Proxy
- Classifications
- CWE-290, CWE-306, CWE-289, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Apr 30, 2026CVE publishedPublication date reported by the CVE source.
- Apr 30, 2026Record updatedLatest update available in the CVE record.
Exploitability
Present is not the same as exploitable
Compare your product and version with the public record. A matching version still requires validation against your environment.
Is a vulnerable build present?
Compare these published version ranges with your installed build and any vendor patches.
- Affected versionversion=< 2.11.43
- Affected versionversion=>= 3.0.0-beta1, < 3.6.14
- Affected versionversion=>= 3.7.0-ea.1, < 3.7.0-rc.2
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
- Vendor advisory forwarded-alias request proof of conceptproof of concept · unverified
Labels summarize the accepted research assessment. They do not indicate a test against your environment.
Technologies
Your stack
See the directory against your own environment.
Your stack
Check the software in your environment
Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.
Book a demo