Vulnerability Details : CVE-2021-29471
Synapse is a Matrix reference homeserver written in python (pypi package matrix-synapse). Matrix is an ecosystem for open federated Instant Messaging and VoIP. In Synapse before version 1.33.2 "Push rules" can specify conditions under which they will match, including `event_match`, which matches event content against a pattern including wildcards. Certain patterns can cause very poor performance in the matching engine, leading to a denial-of-service when processing moderate length events. The issue is patched in version 1.33.2. A potential workaround might be to prevent users from making custom push rules, by blocking such requests at a reverse-proxy.
Vulnerability category: Denial of service
Products affected by CVE-2021-29471
- cpe:2.3:a:matrix:synapse:*:*:*:*:*:*:*:*
- cpe:2.3:o:fedoraproject:fedora:34:*:*:*:*:*:*:*
Exploit prediction scoring system (EPSS) score for CVE-2021-29471
0.61%
Probability of exploitation activity in the next 30 days
EPSS Score History
~ 67 %
Percentile, the proportion of vulnerabilities that are scored at or less
CVSS scores for CVE-2021-29471
| Base Score | Base Severity | CVSS Vector | Exploitability Score | Impact Score | Score Source | First Seen |
|---|---|---|---|---|---|---|
|
5.0
|
MEDIUM | AV:N/AC:L/Au:N/C:N/I:N/A:P |
10.0
|
2.9
|
NIST | |
|
5.3
|
MEDIUM | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L |
3.9
|
1.4
|
NIST | |
|
3.7
|
LOW | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:L |
2.2
|
1.4
|
GitHub, Inc. |
CWE ids for CVE-2021-29471
-
The product uses an algorithm or scheme that produces insufficient entropy, leaving patterns or clusters of values that are more likely to occur than others.Assigned by: nvd@nist.gov (Primary)
-
The product does not properly control the allocation and maintenance of a limited resource.Assigned by: security-advisories@github.com (Secondary)
References for CVE-2021-29471
-
https://github.com/matrix-org/synapse/releases/tag/v1.33.2
Release v1.33.2 · matrix-org/synapse · GitHubRelease Notes;Third Party Advisory
-
https://github.com/matrix-org/synapse/commit/03318a766cac9f8b053db2214d9c332a977d226c
Merge pull request from GHSA-x345-32rc-8h85 · matrix-org/synapse@03318a7 · GitHubPatch;Third Party Advisory
-
https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/TNNAJOZNMVMXM6AS7RFFKB4QLUJ4IFEY/
[SECURITY] Fedora 34 Update: matrix-synapse-1.38.1-1.fc34 - package-announce - Fedora Mailing-ListsMailing List;Third Party Advisory
-
https://github.com/matrix-org/synapse/security/advisories/GHSA-x345-32rc-8h85
Denial of service attack via push rule patterns · Advisory · matrix-org/synapse · GitHubPatch;Third Party Advisory
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