Unauthenticated middleware bypass via encoded request paths
Published Dec 9, 2025 · Updated Dec 9, 2025
Interpretation conflict in Traefik Proxy 1.7.34 and earlier, 2.x before 2.11.32, and 3.x before 3.6.3 allows remote attackers to bypass middleware. Traefik evaluates Path, PathPrefix, and PathRegex rules before decoding or normalizing the path, then forwards the decoded path through another router. Exploitation requires path-based routing where another router exposes the same backend, allowing protected functionality to be reached without its middleware.
Summary
What happened
Interpretation conflict in Traefik Proxy 1.7.34 and earlier, 2.x before 2.11.32, and 3.x before 3.6.3 allows remote attackers to bypass middleware. Traefik evaluates Path, PathPrefix, and PathRegex rules before decoding or normalizing the path, then forwards the decoded path through another router. Exploitation requires path-based routing where another router exposes the same backend, allowing protected functionality to be reached without its middleware.
The record
- CVE
- CVE-2025-66490
- Published
- Dec 9, 2025
- Updated
- Dec 9, 2025
- Vendor
- Traefik Labs
- Product
- Traefik Proxy
- Classifications
- CWE-436, T1190
- Attack vector
- network
- Privileges
- unauthenticated
Timeline
How it unfolded
- Dec 9, 2025CVE publishedPublication date reported by the CVE source.
- Dec 9, 2025Record 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=github.com/traefik/traefik <= 1.7.34
- Affected versionversion=github.com/traefik/traefik/v2 < 2.11.32
- Affected versionversion=github.com/traefik/traefik/v3 < 3.6.3
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.
Public exploit references
- Encoded-path middleware bypass 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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