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High, CVSS 8.2amended

Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders

CVE-2024-53863GHSA-vp6v-whfm-rv3g

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (matrix-synapse 1.120.1), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS 4.0
8.2 · 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X · score source
EPSS
  • CVE-2024-53863: 0.61% estimated exploitation activity in the next 30 days; percentile 49.06 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

Impact In Synapse versions before 1.120.1, enabling the dynamicthumbnails 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. 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…

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 3 · amended ·

    Amended from ghsa record GHSA-vp6v-whfm-rv3g

  2. Revision 2 · amended ·

    Reviewed OSV alias/range/CVSS4 correction; package source scopes and original publication preserved. No customer finding resolved.

  3. Revision 1 · created ·

    Published from osv record GHSA-vp6v-whfm-rv3g

Agent brief

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# Patch Next advisory brief: CVE-2024-53863

Advisory: Synapse can be forced to thumbnail unexpected file formats, invoking external, potentially untrustworthy decoders
IDs: CVE-2024-53863, GHSA-vp6v-whfm-rv3g
Record: https://patchnext.com/advisories/cve-2024-53863 (revision 3, source checked 26 Oct 2026, 13:30 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.2)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-synapse 1.120.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-synapse: affected < 1.120.1; fixed in 1.120.1

## Suggested inspection (read-only)
- `python -m pip show matrix-synapse`: prints the installed version. Run with the environment that serves production active.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on matrix-synapse.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://osv.dev/vulnerability/GHSA-vp6v-whfm-rv3g (OSV record GHSA-vp6v-whfm-rv3g lists affected ranges: PyPI matrix-synapse >=0 <1.120.1 (fixed))
- Verified: https://github.com/advisories/GHSA-vp6v-whfm-rv3g (GitHub-reviewed advisory GHSA-vp6v-whfm-rv3g lists affected ranges: PyPI matrix-synapse >=0 <1.120.1)

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