Sydent vulnerable to 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.
Affected software
Click a technology to see all vulnerabilities affecting it.
| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Python (PyPI) | matrix-sydent | < 2.3.0 | 2.3.0 |
References
- https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7
- https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d
- https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428
- https://github.com/matrix-org/sydent/security/advisories/GHSA-wmg4-8cp2-hpg9
- https://pypi.org/project/matrix-sydent/
- https://github.com/matrix-org/sydent/releases/tag/v2.3.0
- https://nvd.nist.gov/vuln/detail/CVE-2021-29430
- https://github.com/matrix-org/sydent
- https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-21.yaml
- https://pypi.org/project/matrix-sydent
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H- Weakness (CWE)
CWE-20, CWE-400, CWE-770- Platform
- Python (PyPI)
- Package
matrix-sydent- Disclosed
- 15.04.2021
- Updated
- 11.10.2026 15:17
Sources and licenses
OSV / GitHub Advisory Database - PYSEC-2021-21 - PyPA Advisory Database; CC BY 4.0
OSV / GitHub Advisory Database - GHSA-wmg4-8cp2-hpg9 - CC BY 4.0
Vulnerability history: matrix-sydent
All published vulnerabilities of this package (Python (PyPI)), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 7
- First → latest
- 05.2019 07.2023
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- High 2
- Medium 4
Disclosures per year
- 2019: 1
- 2020: 0
- 2021: 4
- 2022: 1
- 2023: 1
- 2024: 0
- 2025: 0
- 2026: 0
-
Sydent vulnerable to denial of service attack via memory exhaustion this entry
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