CVE-2024-53863: Matrix Synapse Thumbnail Processing Vulnerability
Summary
CVE-2024-53863: 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 invok... Affects matrix-synapse versions < 1.120.1. Fixed in 1.120.1. How to fix ↓
Also tracked for
- matrix-synapse · Debian:13
The same CVE-2024-53863 is tracked separately for each ecosystem and vendor. Its fix information is the same; the package and affected versions differ.
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Background
Matrix Synapse is an open-source server implementation of the Matrix protocol, enabling real-time communication and collaboration. It supports various functionalities, including messaging, voice, and video calls. However, prior to version 1.120.1, Synapse had a vulnerability related to its thumbnail generation feature, which could be exploited to process unexpected file formats, potentially leading to security risks.
Vulnerability Detail
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. This could invoke external tools like Ghostscript for processing, significantly expanding the attack surface in a historically vulnerable area. The risk associated with this vulnerability is considerable, especially since these uncommon formats are rarely used in the open web or within the Matrix ecosystem.
How To Fix
Latest published version: 1.163.0 as of 22 Oct 2026
pip install --upgrade "matrix-synapse==1.163.0"Upgrading to it may include breaking changes; the version below is the minimum fixed release for this vulnerability.
If you need the minimum change
1.120.1
This is the first release that contains the fix.
pip install --upgrade "matrix-synapse==1.120.1"Tip — Not sure which version your app runs? Vulert can match this fix to it. Scan free →
Workaround
Ensure that any image codecs and helper programs, such as Ghostscript, are patched against known security vulnerabilities. Additionally, uninstall any unused image decoder libraries and helper programs from the system environment where Synapse is running. Note that some decoder libraries may be bundled with Pillow and cannot be easily uninstalled. The official Docker container image does not include Ghostscript.
Conclusion
The CVE-2024-53863 vulnerability in Matrix Synapse poses significant risks due to its ability to process unexpected file formats for thumbnail generation. Updating to version 1.120.1 or later is crucial to mitigate these risks. Additionally, implementing the suggested workarounds can further enhance security.
See every vulnerability recorded for matrix-synapse →
FAQ
CVE-2024-53863 is a vulnerability in Matrix Synapse that allows the processing of unexpected file formats for thumbnail generation, potentially invoking untrusted external decoders.
You can use Vulert's playground at Vulert Scanner to check if your application is affected by this vulnerability without requiring any signup.
The vulnerability significantly expands the attack surface, allowing potential exploitation through uncommon image formats that could invoke external tools, leading to security breaches.
You can update Matrix Synapse to the patched version by running the command: 'pip install --upgrade matrix-synapse'.
After the patch, Matrix Synapse restricts thumbnail generation to widely used formats: PNG, JPEG, GIF, and WebP.
References
Related vulnerabilities
Recent vulnerabilities recorded for matrix-synapse.
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