Bug 2550374 (CVE-2026-86412)

Summary:	CVE-2026-86412 curl: curl: server-set cookie erases cookie jar
Product:	[Other] Security Response	Reporter:	OSIDB Bzimport <bzimport>
Component:	vulnerability	Assignee:	Product Security <prodsec-ir-bot>
Status:	NEW ---	QA Contact:
Severity:	low	Docs Contact:
Priority:	low
Version:	unspecified	CC:	anthomas, csutherl, ehelms, ggainey, jclere, jpasqual, juwatts, mdellweg, mhulan, nmoumoul, osousa, pcreech, pjindal, plodge, rchan, rekumar, rhel-process-autobot, security-response-team, smallamp, szappis, tmalecek, vchlup, vvoronko, watson-tool-maintainers
Target Milestone:	---	Keywords:	Security
Target Release:	---
Hardware:	All
OS:	Linux
Whiteboard:
Fixed In Version:		Doc Type:	---
Doc Text:		Story Points:	---
Clone Of:		Environment:
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Regression:	---	Mount Type:	---
Documentation:	---	CRM:
Verified Versions:		Category:	---
oVirt Team:	---	RHEL 7.3 requirements from Atomic Host:
Cloudforms Team:	---	Target Upstream Version:
Embargoed:
Deadline:	2026-10-14

Description OSIDB Bzimport 2026-10-13 11:55:55 UTC

server-set cookie erases cookie jar
===================================

Project curl Security Advisory, October 14 2026
[Permalink](https://curl.se/docs/CVE-2026-86412.html)

VULNERABILITY
-------------

A remote HTTP server can set a cookie that curl accepts and writes to a
Netscape cookie jar but cannot reload. On the next invocation using the same
path for `--cookie` and `--cookie-jar`, curl fails before connecting, then the
cleanup procedure replaces the jar with an empty file, deleting cookies for
unrelated domains.

INFO
----

The root cause is that curl can accept a cookie over the wire and store it in
its cookie file, but refuse to later load it because of size constraints. When
a single cookie entry is considered problematic, the entire cookie load
process was abandoned. The subsequent cookie store operation then writes the
file with a partial set, erasing cookies that were otherwise assumed to
remain.

A cookie with a 4094-byte name, value `v`, and `Path=/` followed by 870 `a`
characters, set by a 16-byte host (`attacker.example`), serializes to a
4999-byte cookie jar record. This is refused to load because curl has a 5000
byte line limit minus the newline and a null terminator.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name
CVE-2026-86412 to this issue.

CWE-754: Improper Check for Unusual or Exceptional Conditions

Severity: Low

AFFECTED VERSIONS
-----------------

- Affected versions: curl 8.18.0 to and including 8.22.0
- Not affected versions: curl < 8.18.0 and >= 8.23.0
- Introduced-in: https://github.com/curl/curl/commit/3f0629ca443825916cbc0795

libcurl is used by many applications, but not always advertised as such!

This flaw also affects the curl command line tool.

SOLUTION
------------

- Fixed-in: https://github.com/curl/curl/commit/6ded3e594455d6f018fab5f2f5d91

RECOMMENDATIONS
--------------

 A - Upgrade curl to version 8.23.0

 B - Apply the patch to your local version

 C - Do not use cookies

TIMELINE
--------

This issue was reported to the curl project on August 27, 2026.

curl 8.23.0 was released on October 14, 2026, coordinated with the publication
of this advisory.

CREDITS
-------

- Reported-by: Stanislav Fort (Aisle Research)
- Patched-by: Daniel Stenberg

Thanks a lot!