{"id":"CVE-2021-29430","aliases":["GHSA-wmg4-8cp2-hpg9","PYSEC-2021-21"],"url":"https://o3.security/vulnerability/CVE-2021-29430","summary":"Sydent vulnerable to denial of service attack via memory exhaustion","details":"### Impact\n\nSydent 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.\n\nSydent 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.\n\nThis affects any server which accepts registration requests from untrusted clients.\n\n### Patches\n\nPatched by 89071a1, 0523511, f56eee3.\n\n### Workarounds\n\nRequest sizes can be limited in an HTTP reverse-proxy.\n\nThere are no known workarounds for the problem with overlarge responses.\n\n### For more information\n\nIf you have any questions or comments about this advisory, email us at security@matrix.org.","published":"2021-04-15T21:15:17.413Z","modified":"2026-10-20T10:54:37.135231150Z","cvss":{"score":7.5,"severity":"HIGH","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H"},"epss":{"score":0.01833,"percentile":0.76937,"asOf":"2026-08-23"},"cisaKev":null,"exploitsKnown":0,"affectedPackages":[{"ecosystem":"PyPI","name":"matrix-sydent","fixedVersion":"2.3.0"}],"fix":{"url":"https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7","label":"matrix-org/sydent@0523511"},"references":[{"type":"ADVISORY","url":"https://github.com/matrix-org/sydent/releases/tag/v2.3.0"},{"type":"FIX","url":"https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7"},{"type":"FIX","url":"https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d"},{"type":"FIX","url":"https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428"},{"type":"FIX","url":"https://github.com/matrix-org/sydent/security/advisories/GHSA-wmg4-8cp2-hpg9"},{"type":"PACKAGE","url":"https://pypi.org/project/matrix-sydent/"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2021-29430"},{"type":"PACKAGE","url":"https://github.com/matrix-org/sydent"},{"type":"WEB","url":"https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-21.yaml"},{"type":"WEB","url":"https://pypi.org/project/matrix-sydent"}],"provenance":{"sources":["OSV.dev","FIRST.org (EPSS)"],"lastVerified":"2026-10-20T10:54:37.135231150Z"}}