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 only a slash as path (`path="/"`). Since this site is not secure, the cookie *should* 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.
Fix
Patch, vendor advisory and mitigation references on NVD 3
- https://curl.se/docs/CVE-2025-9086.html Patch, Vendor Advisory
- https://curl.se/docs/CVE-2025-9086.json Vendor Advisory
- http://www.openwall.com/lists/oss-security/2025/09/10/1 Mailing List, Patch, Third Party Advisory
Every line above is quoted from NVD, CISA, Microsoft, the vendor's own advisory or DISA; nothing is generated.
Change history 1
- First seenCVSS 7.5 · haxx, debianNVD modified 2026-10-19 17:10
Affected (CPE criteria) 2
cpe:2.3:a:haxx:curl:*:*:*:*:*:*:*:*cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*
References 7
- https://curl.se/docs/CVE-2025-9086.html Patch, Vendor Advisory
- https://curl.se/docs/CVE-2025-9086.json Vendor Advisory
- https://hackerone.com/reports/3294999 Exploit, Issue Tracking, Third Party Advisory
- http://www.openwall.com/lists/oss-security/2025/09/10/1 Mailing List, Patch, Third Party Advisory
- https://lists.debian.org/debian-lts-announce/2026/01/msg00002.html Mailing List, Third Party Advisory
- https://cert-portal.siemens.com/productcert/html/ssa-089022.html
- https://cert-portal.siemens.com/productcert/html/ssa-253495.html