Path Traversal in Matrix Synapse

CVE-2021-41281

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.

Vulnerability class: Path Traversal (Directory Traversal)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N.

EPSS exploit prediction

EPSS: 0.016 (74.5th percentile), scored .

Low probability of exploitation in the next 30 days, but still tracked. 74th percentile — 74.5% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2021-41281: held from 0.015 to 0.016.

EPSS over last 30 days · oldest: 0.015 · newest: 0.016 · change: +0.001

Affected products

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2021-41281?
CVE-2021-41281 is a high-severity vulnerability in Matrix Synapse, classified under Path Traversal. CVSS score: 7.5/10. Published 2021-11-23.
How severe is CVE-2021-41281?
High severity. CVSS v3 base score is 7.5 out of 10.