matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2019-11842: 1.80% estimated exploitation activity in the next 30 days; percentile 78.45 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

An issue was discovered in Matrix Sydent before 1.0.3 and Synapse before 0.99.3.1. Random number generation is mishandled, which makes it easier for attackers to predict a Sydent authentication token or a Synapse random ID.

Published by the source

24 May 2022, 16:45 UTC

Last modified by the source

13 Jul 2026, 16:42 UTC

Source last checked

26 Oct 2026, 13:21 UTC

1. Revision 3 · amended · 26 Oct 2026

   Amended from ghsa record GHSA-gwf7-vfjf-wf6x

2. Revision 2 · amended · 25 Oct 2026

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

3. Revision 1 · created · 24 Oct 2026

   Published from osv record GHSA-gwf7-vfjf-wf6x

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# Patch Next advisory brief: CVE-2019-11842

Advisory: matrix-sydent and matrix-synapse Use Cryptographically Weak PRNG
IDs: CVE-2019-11842, GHSA-gwf7-vfjf-wf6x
Record: https://patchnext.com/advisories/cve-2019-11842 (revision 3, source checked 26 Oct 2026, 13:21 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-sydent 1.0.3; matrix-synapse 0.99.3.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- PyPI matrix-sydent: affected < 1.0.3; fixed in 1.0.3
- PyPI matrix-synapse: affected < 0.99.3.1; fixed in 0.99.3.1

## Suggested inspection (read-only)
- `python -m pip show matrix-sydent`: prints the installed version. Run with the environment that serves production active.
- `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-sydent, 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-gwf7-vfjf-wf6x (OSV record GHSA-gwf7-vfjf-wf6x lists affected ranges: PyPI matrix-sydent >=0 =0 <0.99.3.1 (fixed))
- Verified: https://github.com/advisories/GHSA-gwf7-vfjf-wf6x (GitHub-reviewed advisory GHSA-gwf7-vfjf-wf6x lists affected ranges: PyPI matrix-sydent >=0 =0 <0.99.3.1)

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