CVE-2025-66491
CVSS 5.9 Medium
- CVSS Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:N/A:N
- Published: 2025-12-09T01:16:55.720
Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation. Setting the annotation to “on” (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected. This issue is fixed in version 3.6.3.
Related CVE by CWE
No related CWE found.
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How to fix CVE-2025-66491
CVE-2025-66491 is a medium severity vulnerability affecting the affected product.
Description: Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation. Setting the annotation to “on” (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected. This issue is fixed in version […]
Affected Versions:
❌ Vulnerable: 3.5.0 - 3.6.2
✅ Safe: ≥ 3.6.3
Exploit Difficulty: MEDIUM
⏱️ Time to exploit: 1-4 hours
🛠️ Required skills: Intermediate security knowledge
💰 Public exploits: May be available
How to Fix:
- Check if you're running the affected product
- Verify version (vulnerable: 3.5.0 - 3.6.2)
- Update to ≥ 3.6.3 or later
- If patching is not immediately possible: restrict network exposure, apply least-privilege access
- Test the fix in a staging environment first
- Review logs for signs of exploitation
- Monitor for IOCs (Indicators of Compromise)
- Enable automatic security updates
- Set up vulnerability monitoring
- Review and harden security configurations
Description: Traefik is an HTTP reverse proxy and load balancer. Versions 3.5.0 through 3.6.2 have inverted TLS verification logic in the nginx.ingress.kubernetes.io/proxy-ssl-verify annotation. Setting the annotation to “on” (intending to enable backend TLS certificate verification) actually disables verification, allowing man-in-the-middle attacks against HTTPS backends when operators believe they are protected. This issue is fixed in version […]
Affected Versions:
❌ Vulnerable: 3.5.0 - 3.6.2
✅ Safe: ≥ 3.6.3
Exploit Difficulty: MEDIUM
⏱️ Time to exploit: 1-4 hours
🛠️ Required skills: Intermediate security knowledge
💰 Public exploits: May be available
How to Fix:
1 Identify affected systems
- Check if you're running the affected product
- Verify version (vulnerable: 3.5.0 - 3.6.2)
2 Immediate actions
- Update to ≥ 3.6.3 or later
- If patching is not immediately possible: restrict network exposure, apply least-privilege access
3 Verification
- Test the fix in a staging environment first
- Review logs for signs of exploitation
- Monitor for IOCs (Indicators of Compromise)
4 Long-term prevention
- Enable automatic security updates
- Set up vulnerability monitoring
- Review and harden security configurations
Exploit Difficulty Assessment
MEDIUM
Time to Exploit: 1-4 hours
Skills Required: Intermediate security knowledge
Public Exploits: May be available
Affected Versions
Vulnerable: 3.5.0 - 3.6.2
Safe: ≥ 3.6.3
Vulnerability Timeline
Dec 09, 2025
Vulnerability Published
CVE details first published to NVD database
Dec 09, 2025
Imported to Database
Added to this CVE tracking system
Detection Rules & IOCs
No specific detection rules generated for this vulnerability type.
No vendor/product data available.