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cookie mixed case PSL bypass

Project curl Security Advisory, December 6 2023 - Permalink


This flaw allows a malicious HTTP server to set "super cookies" in curl that are then passed back to more origins than what is otherwise allowed or possible. This allows a site to set cookies that then would get sent to different and unrelated sites and domains.

It could do this by exploiting a mixed case flaw in curl's function that verifies a given cookie domain against the Public Suffix List (PSL). For example a cookie could be set with domain=co.UK when the URL used a lowercase hostname, even though is listed as a PSL domain.


When curl is built without PSL support, it cannot protect against this problem but it is expected to not allow "too wide" cookies when PSL support is enabled.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2023-46218 to this issue.

CWE-201: Information Exposure Through Sent Data

Severity: Medium


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

This flaw is also accessible using the curl command line tool.


Starting in curl 8.5.0, the code converts both strings to lowercase before checks.


A - Upgrade curl to version 8.5.0

B - Apply the patch to your local version

C - Do not use cookies


This issue was reported to the curl project on October 16, 2023. We contacted distros@openwall on November 28, 2023.

curl 8.5.0 was released on December 6 2023, coordinated with the publication of this advisory.


Thanks a lot!