CVE-2025-9086

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.

CVSS v3.1 Score

7.5

HIGH

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-125 Out-of-bounds Read

Affected Products

Vendor	Product	Versions
haxx	curl	8.13.0 — 8.16.0
debian	debian_linux	All

References

Advisories & Patches

https://curl.se/docs/CVE-2025-9086.html https://curl.se/docs/CVE-2025-9086.json http://www.openwall.com/lists/oss-security/2025/09/10/1

Exploits

https://hackerone.com/reports/3294999

Other References

https://lists.debian.org/debian-lts-announce/2026/01/msg00002.html

Frequently Asked Questions

What is CVE-2025-9086? +

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. It has a CVSS v3.1 base score of 7.5 (HIGH).

How severe is CVE-2025-9086? +

CVE-2025-9086 has a CVSS v3.1 score of 7.5 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-9086? +

CVE-2025-9086 affects products from debian, haxx, specifically: curl, debian_linux. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-9086? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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