Is CVE-2024-53863 in the CISA KEV catalog?

No. CVE-2024-53863 is not currently on the CISA Known Exploited Vulnerabilities list.

What is the CVSS severity of CVE-2024-53863?

CVE-2024-53863 has a CVSS v3 base score of 9.1 (CRITICAL).

What is the EPSS score for CVE-2024-53863?

CVE-2024-53863 has an EPSS score of 0.63% (46th percentile), estimating the probability of exploitation in the next 30 days.

How do I fix CVE-2024-53863?

Upgrade matrix-synapse on debian unstable to 1.121.0-1 or later. Fixes are available for 2 affected products.

CVE & CISA-KEV Catalog

CVE-2024-53863

CRITICAL

9.1

CVSS v3

NVD

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.

CWE-434Unrestricted File Upload

How to fix

Remediation Available

matrix-synapseDebian

Fixed in:1.121.0-1CVE-2024-53863

matrix-synapseUbuntu

Fixed in:0.24.0+dfsg-1ubuntu0.1~esm4USN-7444-1

Fixed in:1.11.0-1ubuntu0.1~esm2USN-7444-1

Fixed in:1.53.0-1ubuntu0.1~esm2USN-7444-1

Remediation is compiled from vendor and distribution security advisories. Always confirm against the linked source for your exact version and platform.

CVSS v3 Vector

Exploitability

Attack VectorNetwork

Attack ComplexityLow

Privileges RequiredNone

User InteractionNone

ScopeUnchanged

Impact

ConfidentialityHigh

IntegrityHigh

AvailabilityNone

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Exploit Intelligence

0.63%probability of exploitation in 30 days

46thpercentile

Moderate risk: more likely to be exploited than 46% of all known CVEs.

References

Vendor Advisory1

github.com

Related Vulnerabilities

Other CWE-434 (Unrestricted File Upload) vulnerabilities, ordered by exploit likelihood. View all

CVE	Severity	CVSS	EPSS	Exploited	Fix
CVE-2017-12617	High	8.1	100%	KEV	Fix
CVE-2018-15961	Critical	9.8	100%	KEV	-
CVE-2021-31207	Medium	6.6	100%	KEV + Ransom	Fix
CVE-2017-12615	High	8.1	100%	KEV + Ransom	-
CVE-2025-31324	Critical	10.0	99%	KEV + Ransom	-
CVE-2024-50623	Critical	9.8	99%	KEV + Ransom	Fix

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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2025-08-26.