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High, CVSS 7.5amended

Matrix Synapse DoS

CVE-2018-10657GHSA-vmcc-4p4x-x7wg

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (matrix-synapse 0.28.1), 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
7.5 · CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
  • CVE-2018-10657: 1.49% estimated exploitation activity in the next 30 days; percentile 74.18 (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.

Matrix Synapse before 0.28.1 is prone to a denial of service flaw where malicious events injected with depth = 2<sup63</sup - 1 render rooms unusable, related to federation/federationbase.py and handlers/message.py, as exploited in the wild in April 2018.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 2 · amended ·

    Amended from ghsa record GHSA-vmcc-4p4x-x7wg

  2. Revision 1 · created ·

    Published from osv record GHSA-vmcc-4p4x-x7wg

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2018-10657

Advisory: Matrix Synapse DoS
IDs: CVE-2018-10657, GHSA-vmcc-4p4x-x7wg
Record: https://patchnext.com/advisories/cve-2018-10657 (revision 2, source checked 26 Oct 2026, 13:12 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-synapse 0.28.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-synapse: affected < 0.28.1; fixed in 0.28.1

## 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-vmcc-4p4x-x7wg (OSV record GHSA-vmcc-4p4x-x7wg lists affected ranges: PyPI matrix-synapse >=0 <0.28.1 (fixed))
- Verified: https://github.com/advisories/GHSA-vmcc-4p4x-x7wg (GitHub-reviewed advisory GHSA-vmcc-4p4x-x7wg lists affected ranges: PyPI matrix-synapse >=0 <0.28.1)

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