CVE-2025-66622 matrix-sdk-base is vulnerable to DoS via custom m.room.join_rules event values
Attackers can cause a denial of service in Matrix clients by inviting users to rooms with custom join rules, stalling the sync process.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- A user has to click or open something
- Fix
- Available
What is CVE-2025-66622?
CVE-2025-66622 is a low-severity denial of service vulnerability in matrix-org matrix-rust-sdk, published on 9 Dec 2025. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Official description
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.
Weakness: CWE-755
Which versions are affected by CVE-2025-66622?
3 open source packages ship an affected version, including matrix-sdk-base. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
matrix-sdk-base crates.io | All versions | 0.16.0 |
matrix-sdk-base crates.io | All versions | 0.16.0 |
matrix-sdk-base crates.io | From 0.0.0-0 | 0.16.0 |
Products include Matrix Matrix-Rust-Sdk.
How do I fix CVE-2025-66622?
Upgrade matrix-sdk-base to 0.16.0 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-66622 being exploited?
There is no known exploitation of CVE-2025-66622 in the wild and no public exploit code.
Other vulnerabilities in matrix-org matrix-rust-sdk
Sources
Also known as GHSA-jj6p-3m75-g2p3, RUSTSEC-2025-0135.