matrix-sdk-base denial of service via custom m.room.join_rules event values

Exploitation

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

CVSS 4.0

1.3 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:P/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N/E:U · score source

EPSS

• CVE-2025-66622: 0.41% estimated exploitation activity in the next 30 days; percentile 35.63 (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.

The matrix-sdk-base crate is unable to handle responses that include custom m.room.joinrules values due to a serialization bug. This can be exploited to cause a denial-of-service condition, if a user is invited to a room with non-standard join rules, the crate's sync process will stall, preventing further processing for all rooms. Patches The issue is fixed in matrix-sdk-base 0.16.0. Workarounds Users can leave affected rooms on another client to mitigate the issue. References The issue was fixed in https://github.com/matrix-org/matrix-rust-sdk/pull/5924.

Published by the source

8 Dec 2025, 22:07 UTC

Last modified by the source

9 Dec 2025, 19:17 UTC

Source last checked

26 Oct 2026, 15:39 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-jj6p-3m75-g2p3

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# Patch Next advisory brief: CVE-2025-66622

Advisory: matrix-sdk-base denial of service via custom m.room.join_rules event values
IDs: CVE-2025-66622, GHSA-jj6p-3m75-g2p3
Record: https://patchnext.com/advisories/cve-2025-66622 (revision 1, source checked 26 Oct 2026, 15:39 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: Low (CVSS 1.3)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: matrix-sdk-base 0.16.0. A vendor fix does not mean a deployment is fixed.

## Affected components
- crates.io matrix-sdk-base: affected < 0.16.0; fixed in 0.16.0

## Suggested inspection (read-only)
- crates.io matrix-sdk-base: check the installed version with your package manager.

## 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-sdk-base.
- 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://github.com/advisories/GHSA-jj6p-3m75-g2p3 (GitHub-reviewed advisory GHSA-jj6p-3m75-g2p3 lists affected ranges: crates.io matrix-sdk-base >=0 <0.16.0)

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