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Bad local IPv6 connection reuse

Project curl Security Advisory, April 27 2022 - Permalink


libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse, if one of them matches the setup.

Due to errors in the logic, the config matching function did not take the IPv6 address zone id into account which could lead to libcurl reusing the wrong connection when one transfer uses a zone id and a subsequent transfer uses another (or no) zone id.


Zone ids are only used for non-global scoped IPv6 addresses and they are only used when specifying the address numerically.

This flaw has existed in curl since commit 2d0e9b40d3237b1, shipped in libcurl 7.65.0, released on May 22 2019. Previous versions instead do not accept URLs with zone ids.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2022-27775 to this issue.

CWE-200: Exposure of Sensitive Information to an Unauthorized Actor

Severity: Low


Also note that libcurl is used by many applications, and not always advertised as such.



A - Upgrade curl to version 7.83.0

B - Apply the patch to your local version

C - Do not use non-global numerical IPv6 addresses in URLs to curl


This issue was reported to the curl project on April 21, 2022. We contacted distros@openwall on April 21.

libcurl 7.83.0 was released on April 27 2022, coordinated with the publication of this advisory.


Thanks a lot!