curl / Docs / Security Problems / Wrong content via metalink not discarded

Wrong content via metalink not discarded

Project curl Security Advisory, July 21th 2021 - Permalink

VULNERABILITY

When curl is instructed to download content using the metalink feature, the contents is verified against a hash provided in the metalink XML file.

The metalink XML file points out to the client how to get the same content from a set of different URLs, potentially hosted by different servers and the client can then download the file from one or several of them. In a serial or parallel manner.

If one of the servers hosting the contents has been breached and the contents of the specific file on that server is replaced with a modified payload, curl should detect this when the hash of the file mismatches after a completed download. It should remove the contents and instead try getting the contents from another URL. This is not done, and instead such a hash mismatch is only mentioned in text and the potentially malicious content is kept in the file on disk.

There's a risk the user doesn't notice the message and instead assumes the file is fine.

We are not aware of any exploit of this flaw.

INFO

This flaw exists only in the curl tool. libcurl is not affected.

This flaw has existed in curl since commit b5fdbe848bc3d in curl 7.27.0, released on July 27, 2012.

The Common Vulnerabilities and Exposures (CVE) project has assigned the name CVE-2021-22922 to this issue.

CWE-20: Improper Input Validation

Severity: Medium

AFFECTED VERSIONS

THE SOLUTION

curl has completely removed the metalink feature as of 7.78.0. No fix for this flaw will be produced by the curl project.

The fix for earlier versions is to rebuild curl with the metalink support switched off!

RECOMMENDATIONS

A - Upgrade curl to version 7.78.0

B - Make sure you do not use metalink with curl

C - Disable metalink in your build

TIMELINE

This issue was reported to the curl project on May 30, 2021.

This advisory was posted on Jul 21, 2021.

CREDITS

This issue was reported by Harry Sintonen. Patched by Daniel Stenberg.

Thanks a lot!