Summary
matrix-sdk-base denial of service via custom m.room.join_rules event values
The matrix-sdk-base crate is 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.
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.
Impact
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The issue is fixed in matrix-sdk-base 0.16.0.
Frequently Asked Questions
- What is CVE-2025-66622? CVE-2025-66622 is a low-severity security vulnerability in matrix-sdk-base (rust), affecting versions < 0.16.0. It is fixed in 0.16.0.
- Which versions of matrix-sdk-base are affected by CVE-2025-66622? matrix-sdk-base (rust) versions < 0.16.0 is affected.
- Is there a fix for CVE-2025-66622? Yes. CVE-2025-66622 is fixed in 0.16.0. Upgrade to this version or later.
- Is CVE-2025-66622 exploitable, and should I be worried? Whether CVE-2025-66622 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2025-66622 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2025-66622? Upgrade
matrix-sdk-baseto 0.16.0 or later.