CVE-2021-41281

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.

How to fix CVE-2021-41281

To remediate CVE-2021-41281, upgrade the affected package to a fixed version below.

• —upgrade to 1.47.1-1 or later
• —upgrade to 1.47.1 or later
• —upgrade to 91f2bd0907f1d05af67166846988e49644eb650c or later

Is CVE-2021-41281 being exploited?

Low — EPSS is 0.5%, meaning exploitation activity has not been observed at scale.

Affected packages (3)

• from 0, < 1.47.1-1
• from 0, < 1.47.1
• from 0, < 91f2bd0907f1d05af67166846988e49644eb650c | from 0, < 1.47.1

CVSS scores

References (9)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2021-41281
• ADVISORYsecurity-tracker.debian.org/tracker/CVE-2021-41281
• PATCHgithub.com/matrix-org/synapse
• WEBgithub.com/matrix-org/synapse/commit/91f2bd090
• WEB