CVE-2026-6253

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

Affected products

Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.

References

• https://curl.se/docs/CVE-2026-6253.json ↗
• https://curl.se/docs/CVE-2026-6253.html ↗
• https://hackerone.com/reports/3669637 ↗
• http://www.openwall.com/lists/oss-security/2026/04/29/11 ↗