{"cve":"CVE-2021-29430","nvd":{"published":"2021-04-15T21:15:17.413","modified":"2026-06-17T03:47:37.550","status":"Modified","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.","cvss_v4":null,"cvss_v3":{"version":"3.1","vector":"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H","score":7.5},"cwes":["CWE-770","CWE-20","CWE-400"],"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/releases/tag/v2.3.0","https://github.com/matrix-org/sydent/security/advisories/GHSA-wmg4-8cp2-hpg9"],"products":["matrix:sydent"],"source":"nvd","synced_at":"2026-10-19T21:17:01.373894544+00:00"},"epss":{"cve":"CVE-2021-29430","score":0.01833,"percentile":0.78912,"date":"2026-11-01"},"kev":null,"osv":[{"id":"GHSA-wmg4-8cp2-hpg9","url":"https://osv.dev/vulnerability/GHSA-wmg4-8cp2-hpg9","summary":"Sydent vulnerable to denial of service attack via memory exhaustion","modified":"2026-09-10T03:49:26.904044812Z","packages":[{"ecosystem":"PyPI","name":"matrix-sydent","purl":"pkg:pypi/matrix-sydent","ranges":["<2.3.0"],"fixed":["2.3.0"]}]},{"id":"PYSEC-2021-21","url":"https://osv.dev/vulnerability/PYSEC-2021-21","summary":"","modified":"2023-11-08T04:05:33.651530Z","packages":[{"ecosystem":"PyPI","name":"matrix-sydent","purl":"pkg:pypi/matrix-sydent","ranges":["<2.3.0"],"fixed":["2.3.0"]}]}],"attribution":["This product uses the NVD API but is not endorsed or certified by the NVD.","EPSS scores: FIRST Exploit Prediction Scoring System, https://www.first.org/epss","Known exploited vulnerabilities: CISA Known Exploited Vulnerabilities Catalog, https://www.cisa.gov/known-exploited-vulnerabilities-catalog","Package advisories: OSV (https://osv.dev), from the GitHub Advisory Database, PyPA, Go, RustSec and other ecosystem databases, under CC-BY 4.0 or CC0","CVE records: the CVE Program's CVE List (https://www.cve.org), under its terms of use (https://www.cve.org/Legal/TermsOfUse). CVE is a registered trademark of The MITRE Corporation; this product is not affiliated with the CVE Program."]}