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🛡️ CVE-2024-53863 — matrix-synapse

🔴 CVSS 9.1 — Critical ✅ No Known Exploit CWE-434 NVD
9.1
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders

Impact

In Synapse versions before 1.120.1, enabling the dynamic_thumbnails option or processing a specially crafted request could trigger the decoding and thumbnail generation of uncommon image formats, potentially invoking external tools like Ghostscript for processing.

This significantly expands the attack surface in a historically vulnerable area, presenting a risk that far outweighs the benefit, particularly since these formats are rarely used on the open web or within the Matrix ecosystem.

For a list of image formats, as well as decoding libraries and helper programs used, see [the Pillow documentation](https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html).

Patches

Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP.

Workarounds

  • Ensure any image codecs and helper programs, such as Ghostscript, are patched against security vulnerabilities.
  • Uninstall unused image decoder libraries and helper programs, such as Ghostscript, from the system environment that Synapse is running in.
  • Depending on the installation method, there may be some decoder libraries bundled with Pillow and these cannot be easily uninstalled.
  • The official Docker container image does not include Ghostscript.

References

  • [The Pillow documentation](https://pillow.readthedocs.io/en/stable/handbook/image-file-formats.html) includes a list of supported image formats and which libraries or helper programs are used to decode them.

For more information

If you have any questions or comments about this advisory, please email us at [security at element.io](mailto:[email protected]).

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. The scope is unchanged, so the impact stays within the vulnerable component. Rated impact: confidentiality high, integrity high, availability none.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Unchanged — the damage stays inside the vulnerable component.
  • Confidentiality impact: High — total loss, or loss the attacker controls.
  • Integrity impact: High — total loss, or loss the attacker controls.
  • Availability impact: None.

Weakness class

CVE-2024-53863 is classified as CWE-434: Unrestricted Upload of File with Dangerous Type. Uploads are accepted without restricting type, so an executable file can be placed where the server will run it.

Affected software

CVE-2024-53863 is recorded against 2 packages.

  • matrix-synapse (fixed in 1.120.1)
  • synapse (fixed in 1.120.1)

Timeline and source

Published on 7 July 2026. No public exploit is currently recorded for this entry. Record sourced from NVD.

References

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

Other advisories for this package

matrix-synapse has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-434: Unrestricted Upload of File with Dangerous Type) in other software:

CVE-2024-53863 on other distributions

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

Details

Severity HIGH
CVSS Score 9.1
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
CWE CWE-434
Public Exploit ✅ No
Source NVD
Published 2026-07-07
Updated 2026-08-20
Modified 2026-07-07
Fix URL N/A

Affected Packages

Software From version Fixed in
matrix-synapse — 1.120.1
synapse — 1.120.1

Exploit Protection

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CVE-2024-53863 carries CVSS 9.1 Critical rating. BotEraser checks your installation against this and other known CVE records, and blocks IPs associated with exploit activity.

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