CVE-2024-53863: Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders
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.
Classification
CVE ID: CVE-2024-53863
CVSS Base Severity: HIGH
CVSS Base Score: 8.2
Affected Products
Vendor: element-hq
Product: synapse
Exploit Prediction Scoring System (EPSS)
EPSS Score: 0.04% (probability of being exploited)
EPSS Percentile: 11.44% (scored less or equal to compared to others)
EPSS Date: 2025-02-03 (when was this score calculated)