🛡️ CVE-2021-41281 — matrix-synapse

🟠 CVSS 8.0 — High ✅ No Known Exploit CWE-22 OSV
8.0
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Path traversal in Matrix Synapse

Impact

Synapse instances with the media repository enabled can be tricked into downloading a file from a remote server into an arbitrary directory, potentially outside the media store directory.

The last two 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 configured with a federation whitelist are also unaffected.

Patches

Server administrators should upgrade to 1.47.1 or later.

Workarounds

Server administrators using a reverse proxy could, at the expense of losing media functionality, block the following endpoints:

  • /_matrix/media/r0/download/{serverName}/{mediaId}
  • /_matrix/media/r0/download/{serverName}/{mediaId}/{fileName}
  • /_matrix/media/r0/thumbnail/{serverName}/{mediaId}

Alternatively, non-containerized deployments can be adapted to use the hardened systemd config, located at contrib/systemd/override-hardened.conf.

References

n/a

For more information

If you have any questions or comments about this advisory, e-mail us at security@matrix.org.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. Rated impact: confidentiality none, integrity high, availability none.

Weakness class

CVE-2021-41281 is classified as CWE-22: Path Traversal. A file path built from user input is not confined to the intended directory, letting an attacker reach files elsewhere on the filesystem.

Affected software

CVE-2021-41281 is recorded against 1 package.

  • matrix-synapse (fixed in 1.47.1)

Timeline and source

Published on 23 November 2021 and last revised on 8 July 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from OSV.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Package)
github.com (Web)
github.com (Web)
lists.fedoraproject.org (Web)
lists.fedoraproject.org (Web)

CVE-2021-41281 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.0
CVSS Vector CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
CWE CWE-22
Public Exploit ✅ No
Source OSV
Published 2021-11-23
Updated 2026-08-12
Modified 2026-07-08

Affected Packages

Software From version Fixed in
matrix-synapse — 1.47.1

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