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HSTS double free

Project curl Security Advisory, March 20th 2023 - Permalink


libcurl supports sharing HSTS data between separate "handles". This sharing was introduced without considerations for doing this sharing across separate threads but there was no indication of this fact in the documentation.

Due to missing mutexes or thread locks, two threads sharing the same HSTS data could end up doing a double free or use after free.


This feature was not implemented to support sharing between threads. That is still left for future improvements. The fix for this issue is therefore a documentation update clarifying that sharing HSTS between threads is not expected to work.

CWE-415: Double Free

Severity: Low

Severity is set to Low because


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



A - Do not share HSTS data between threads


This issue was reported to the curl project on March 8 2023. We contacted distros@openwall on March 13, 2023.

curl 8.0.0 was released on March 20 2023, coordinated with the publication of this advisory.


Thanks a lot!