# CVE-2025-66622: RUSTSEC-2025-0135 - matrix-sdk-base: Denial of service due to custom `m.room.join_rules` events

Source: https://junglewise.ai/threats/cve-2025-66622-matrix-sdk-base-denial-of-service-via-custom-m-room-join-rules  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2025-12-09  
License: CC BY 4.0 with a link back

CVE-2025-66622 · Severity: high · CVSS 7.5 · Published 2025-12-09

matrix-sdk-base is the base component to build a Matrix client library. Versions 0.14.1 and prior are unable to handle responses that include custom m.room.join_rules 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. This is fixed in version 0.16.0.

Vendors: [crates.io](https://junglewise.ai/threats/vendors/crates-io), [Matrix](https://junglewise.ai/threats/vendors/matrix).

## Quick answers

**Is CVE-2025-66622 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2025-66622 being exploited in the wild.

**How severe is CVE-2025-66622?** High severity, with a CVSS score of 7.5, published 9 December 2025.

**Which products and versions are affected?** matrix-sdk-base (crates.io) SEMVER:introduced=0,fixed=0.16.0, SEMVER:introduced=0.0.0-0,fixed=0.16.0.

**Is there a fix for CVE-2025-66622?** Yes. matrix-sdk-base (crates.io): upgrade to 0.16.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**Am I affected by CVE-2025-66622?** Check whether you run matrix-sdk-base (crates.io) or Matrix-Rust-Sdk at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- matrix-sdk-base (crates.io): upgrade to 0.16.0 or later

  ```sh
  cargo update -p matrix-sdk-base
  ```


## Affected products

- matrix-sdk-base (crates.io) SEMVER:introduced=0,fixed=0.16.0, SEMVER:introduced=0.0.0-0,fixed=0.16.0
- Matrix-Rust-Sdk

## Identifiers

- CVE-2025-66622
- GHSA-jj6p-3m75-g2p3
- RUSTSEC-2025-0135

## Related threats

- [RUSTSEC-2025-0065 - matrix-sdk-base: Panic in the `RoomMember::normalized_power_level()` method](https://junglewise.ai/threats/cve-2025-59047-matrix-sdk-base-panic-in-the-roommember-normalized-power-level)