CVE-2021-29430: Denial of service attack via memory exhaustion
Impact
Sydent does not limit the size of requests it receives from HTTP clients. A malicious user could send an HTTP request with a very large body, leading to disk space exhaustion and denial of service.
Sydent also does not limit response size for requests it makes to remote Matrix homeservers. A malicious homeserver could return a very large response, again leading to memory exhaustion and denial of service.
This affects any server which accepts registration requests from untrusted clients.
Patches
Patched by 89071a1, 0523511, f56eee3.
Workarounds
Request sizes can be limited in an HTTP reverse-proxy.
There are no known workarounds for the problem with overlarge responses.
For more information
If you have any questions or comments about this advisory, email us at security@matrix.org.
Other sources
Sydent is a reference Matrix identity server. Sydent does not limit the size of requests it receives from HTTP clients. A malicious user could send an HTTP request with a very large body, leading to memory exhaustion and denial of service. Sydent also does not limit response size for requests it makes to remote Matrix homeservers. A malicious homeserver could return a very large response, again leading to memory exhaustion and denial of service. This affects any server which accepts registration requests from untrusted clients. This issue has been patched by releases 89071a1, 0523511, f56eee3. As a workaround request sizes can be limited in an HTTP reverse-proxy. There are no known workarounds for the problem with overlarge responses.
Affected Software
Remediation
Event History
Frequently Asked Questions
What is CVE-2021-29430?
CVE-2021-29430 is a vulnerability in the Matrix Sydent identity server that allows a malicious user to send very large HTTP requests, causing memory exhaustion and denial of service.
How severe is CVE-2021-29430?
The severity of CVE-2021-29430 is high, with a severity score of 7.5.
What software is affected by CVE-2021-29430?
Matrix Sydent versions up to and excluding 2.3.0 are affected by CVE-2021-29430.
How can the memory exhaustion and denial of service attack be prevented?
To prevent the memory exhaustion and denial of service attack, it is recommended to update Matrix Sydent to a version that includes the fixed commits: 0523511d2fb40f2738f8a8549868f44b96e5dab7, 89071a1a754c69a50deac89e6bb74002d4cda19d, and f56eee315b6c44fdd9f6aa785cc2ec744a594428.
Is there any additional information available for CVE-2021-29430?
For additional information on CVE-2021-29430, you can refer to the following references: [link1], [link2], [link3].