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curl / Docs / Security Problems / FTP too eager connection reuse

CVE-2023-27535: FTP too eager connection reuse

Project curl Security Advisory, March 20th 2023 - Permalink


libcurl would reuse a previously created FTP connection even when one or more options had been changed that could have made the effective user a very different one, thus leading to the doing the second transfer with wrong credentials.

libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. However, several FTP settings were left out from the configuration match checks, making them match too easily. The settings in questions are CURLOPT_FTP_ACCOUNT, CURLOPT_FTP_ALTERNATIVE_TO_USER, CURLOPT_FTP_SSL_CCC and CURLOPT_USE_SSL level.

We are not aware of any exploit of this flaw.


CVE-2023-27535 was introduced in commit 177dbc7be07125582, shipped in curl 7.13.0.

CWE-305: Authentication Bypass by Primary Weakness

Severity: Medium


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


A fix for CVE-2023-27535


A - Upgrade curl to version 8.0.0

B - Apply the patch to your local version


This issue was reported to the curl project on March 5, 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!