---
id: CVE-2024-53863
aliases:
  - GHSA-vp6v-whfm-rv3g
  - PYSEC-2026-1615
title: >-
  Synapse can be forced to thumbnail unexpected file formats, invoking external,
  potentially untrustworthy decoders
summary: >-
  Synapse can be forced to thumbnail unexpected file formats, invoking external,
  potentially untrustworthy decoders
severity: high
vendor: matrix-synapse
product: matrix-synapse
ecosystem: pip
affected:
  - matrix-synapse < 1.120.1
patched:
  - matrix-synapse 1.120.1
published: '2024-12-03'
updated: '2026-07-07'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-vp6v-whfm-rv3g'
references:
  - url: >-
      https://github.com/element-hq/synapse/security/advisories/GHSA-vp6v-whfm-rv3g
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2024-53863'
  - url: 'https://github.com/element-hq/synapse'
tags:
  - osv
  - pip
epss: 0.00606
epssPercentile: 0.47714
ingestedAt: '2026-07-08T18:25:53.351Z'
---

## Overview

### 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:security@element.io).


## Affected packages

- `matrix-synapse < 1.120.1`

## Remediation

Upgrade to a patched release:

- `matrix-synapse 1.120.1`