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curl / Docs / Security Problems / SSH connection too eager reuse still
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CVE-2023-27538: SSH connection too eager reuse still

Project curl Security Advisory, March 20th 2023 - Permalink

VULNERABILITY

libcurl would reuse a previously created connection even when an SSH related option had been changed that should have prohibited reuse.

libcurl keeps previously used connections in a connection pool for subsequent transfers to reuse if one of them matches the setup. However, two SSH settings were left out from the configuration match checks, making them match too easily.

We are not aware of any exploit of this flaw.

INFO

These are the options that were not considered in the check, so curl would reuse a connection even if the subsequent transfer would have changed one or more of these options.

This flaw was initially introduced in curl 7.16.1.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2023-27538 to this issue.

This vulnerability is partially identical to CVE-2022-27782 since the fix for that previous issue was bad and did not actually correct the problem for these SSH options.

CWE-305: Authentication Bypass by Primary Weakness

The previos flaw CVE-2022-27782 was set to severity Medium, but since this is a partial of that and affects only two options that rarely will change with the expectation that the user will be different, this time we set it severity Low.

Severity: Low

AFFECTED VERSIONS

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

THE SOLUTION

The fix for CVE-2023-27538

RECOMMENDATIONS

A - Upgrade curl to version 8.0.0

B - Apply the patch to your local version

C - Avoid SCP and SFTP transfers

TIMELINE

This issue was reported to the curl project on March 9 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.

CREDITS

Thanks a lot!