Description
curl might erroneously pass on credentials for a first proxy to a second proxy.
This can happen when the following conditions are true:
1. curl is setup to use specific different proxies for different URL schemes 2. the first proxy needs credentials 3. the second proxy uses no credentials 4. while using the first proxy (using say `http://`), curl is asked to follow a redirect to a URL using another scheme (say `https://`), accessed using a second, different, proxy
Metrics
CVSS 3.1 5.9/10
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:HWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| curl | curl | >= 7.14.1, < 8.14.2; >= 8.15.0, < 8.16.1; >= 8.17.0, < 8.20.0 |
| curl | curl | >= 3b60bb725913ce7339aefef0a14b12df4c24db60, < 188c2f166a20fa97c2325b2da7d0e5cecc13725f |
| curl | curl | 8.19.0; 8.18.0; 8.17.0; 8.16.0; 8.15.0; 8.14.1; 8.14.0; 8.13.0; 8.12.1; 8.12.0; 8.11.1; 8.11.0; 8.10.1; 8.10.0; 8.9.1; 8.9.0; 8.8.0; 8.7.1; 8.7.0; 8.6.0 |
References
- https://curl.se/docs/CVE-2026-6253.htmlPatch, Vendor Advisory
- https://curl.se/docs/CVE-2026-6253.jsonVendor Advisory
- https://hackerone.com/reports/3669637Exploit, Issue Tracking, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2026/04/29/11Mailing List, Patch, Third Party Advisory
- https://hackerone.com/reports/3669637Exploit, Issue Tracking, Third Party Advisory
Timeline
- Published
- May 13, 2026
- Last modified
- Nov 11, 2026
- NVD status
- Modified