{"id":"CVE-2021-29430","aliases":["GHSA-wmg4-8cp2-hpg9","PYSEC-2021-21"],"title":"Sydent vulnerable to denial of service attack via memory exhaustion","summary":"Sydent vulnerable to denial of service attack via memory exhaustion","severity":"high","cvss":7.5,"cvssVector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","vendor":"matrix-sydent","product":"matrix-sydent","ecosystem":"pip","affected":["matrix-sydent < 2.3.0"],"patched":["matrix-sydent 2.3.0"],"published":"2021-04-19","updated":"2026-09-10","sourceUpdated":"2026-09-10T03:49:26.904044812Z","source":"OSV","sourceUrl":"https://osv.dev/vulnerability/GHSA-wmg4-8cp2-hpg9","references":[{"url":"https://github.com/matrix-org/sydent/security/advisories/GHSA-wmg4-8cp2-hpg9"},{"url":"https://nvd.nist.gov/vuln/detail/CVE-2021-29430"},{"url":"https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7"},{"url":"https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d"},{"url":"https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428"},{"url":"https://github.com/matrix-org/sydent"},{"url":"https://github.com/matrix-org/sydent/releases/tag/v2.3.0"},{"url":"https://github.com/pypa/advisory-database/tree/main/vulns/matrix-sydent/PYSEC-2021-21.yaml"},{"url":"https://pypi.org/project/matrix-sydent"}],"tags":["osv","pip"],"epss":0.01833,"epssPercentile":0.77963,"ingestedAt":"2026-09-12T03:13:01.736Z","slug":"CVE-2021-29430","body":"## Overview\n\n### 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.\n\n## Affected packages\n\n- `matrix-sydent < 2.3.0`\n\n## Remediation\n\nUpgrade to a patched release:\n\n- `matrix-sydent 2.3.0`","depth":"twilight","depthScore":42,"depthScoreParts":{"impact":41.3,"likelihood":0.4,"exploitation":0,"ransomware":0},"changes":[]}