CVE-2021-41281 Path traversal in Matrix Synapse

What is CVE-2021-41281?

CVE-2021-41281 is a high-severity path traversal vulnerability in Fedoraproject Fedora, published on 23 Nov 2021. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

Synapse is a package for Matrix homeservers written in Python 3/Twisted. Prior to version 1.47.1, Synapse instances with the media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory. No authentication is required for the affected endpoint. The last 2 directories and file name of the path are chosen randomly by Synapse and cannot be controlled by an attacker, which limits the impact. Homeservers with the media repository disabled are unaffected. Homeservers with a federation whitelist are also unaffected, since Synapse will check the remote hostname, including the trailing `../`s, against the whitelist. Server administrators should upgrade to 1.47.1 or later. Server administrators using a reverse proxy could, at the expense of losing media functionality, may block the certain endpoints as a workaround. Alternatively, non-containerized deployments can be adapted to use the hardened systemd config.

Weakness: CWE-22

Which versions are affected by CVE-2021-41281?

3 open source packages ship an affected version, including matrix-synapse. It affects 2 products.

Products include Fedoraproject Fedora, Matrix Synapse.

How do I fix CVE-2021-41281?

Upgrade matrix-synapse to 1.47.1 or later.

Upgrade, and resolve every user-supplied path against an allowed base folder before opening it. More about Path traversal.

Is CVE-2021-41281 being exploited?

There is no known exploitation of CVE-2021-41281 in the wild and no public exploit code.

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Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-3hfw-x7gx-437c, PYSEC-2021-436, UBUNTU-CVE-2021-41281, openSUSE-SU-2024:11649-1.