CVE-2025-9086

Published: September 11, 2025Last modified: December 15, 2025

Description

1. A cookie is set using the `secure` keyword for `https://target` 2. curl is redirected to or otherwise made to speak with `http://target` (same hostname, but using clear text HTTP) using the same cookie set 3. The same cookie name is set - but with just a slash as path (`path='/'`). Since this site is not secure, the cookie *should* just be ignored. 4. A bug in the path comparison logic makes curl read outside a heap buffer boundary The bug either causes a crash or it potentially makes the comparison come to the wrong conclusion and lets the clear-text site override the contents of the secure cookie, contrary to expectations and depending on the memory contents immediately following the single-byte allocation that holds the path. The presumed and correct behavior would be to plainly ignore the second set of the cookie since it was already set as secure on a secure host so overriding it on an insecure host should not be okay.

Severity score breakdown

Status

References

• http://www.openwall.com/lists/oss-security/2025/09/10/1
• https://curl.se/docs/CVE-2025-9086.html
• https://curl.se/docs/CVE-2025-9086.json
• https://hackerone.com/reports/3294999
• https://lists.debian.org/debian-lts-announce/2026/01/msg00002.html