Backend traffic interception via inverted TLS verification
Published Dec 9, 2025 · Updated Dec 9, 2025
Improper certificate validation in Traefik Proxy 3.5.0 through 3.6.2 allows attackers to intercept HTTPS backend traffic. The ingress-nginx provider sets InsecureSkipVerify to true when proxy-ssl-verify is on, disabling the certificate check the annotation requests. Exploitation requires the experimental provider, an HTTPS backend, the annotation set to on, and control of the backend network path; the reported impact is disclosure of proxied traffic.
Summary
What happened
Improper certificate validation in Traefik Proxy 3.5.0 through 3.6.2 allows attackers to intercept HTTPS backend traffic. The ingress-nginx provider sets InsecureSkipVerify to true when proxy-ssl-verify is on, disabling the certificate check the annotation requests. Exploitation requires the experimental provider, an HTTPS backend, the annotation set to on, and control of the backend network path; the reported impact is disclosure of proxied traffic.
The record
- CVE
- CVE-2025-66491
- Published
- Dec 9, 2025
- Updated
- Dec 9, 2025
- Vendor
- Traefik Labs
- Product
- Traefik Proxy
- Classifications
- CWE-295, T1557
- 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=>= 3.5.0, < 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
No public exploit references are available in this record.
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Technologies
Your stack
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Your stack
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