CVE-2021-29430

Description

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.

How to fix CVE-2021-29430

To remediate CVE-2021-29430, upgrade the affected package to a fixed version below.

• —upgrade to 2.3.0 or later
• —upgrade to 0523511d2fb40f2738f8a8549868f44b96e5dab7 or later

Is CVE-2021-29430 being exploited?

Low — EPSS is 1.4%, meaning exploitation activity has not been observed at scale.

Affected packages (2)

• from 0, < 2.3.0
• from 0, < 0523511d2fb40f2738f8a8549868f44b96e5dab7, < 89071a1a754c69a50deac89e6bb74002d4cda19d, < f56eee315b6c44fdd9f6aa785cc2ec744a594428 | from 0, < 2.3.0

CVSS scores

References (10)

• ADVISORYnvd.nist.gov/vuln/detail/CVE-2021-29430
• PATCHgithub.com/matrix-org/sydent
• PATCHpypi.org/project/matrix-sydent/
• WEBgithub.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7