GHSA-wmg4-8cp2-hpg9 · Severity: high · Ecosystem: pip — Sydent vulnerable to denial of service attack via memory exhaustion
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.
Conclusion & alert: CVE-2021-29430 is rated Moderate Risk (57.1/100): CVSS High severity, with medium exploitation likelihood (EPSS 1.83%). Mandatory action: Review affected assets and schedule remediation.
Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.
EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).
| # | Date | Old EPSS score | New EPSS score | Delta (New - Old) |
|---|---|---|---|---|
| 1 | 2026-06-15 | 1.37% | 1.83% | +0.47% |
| 2 | 2025-03-30 | 1.80% | 1.37% | -0.43% |
| 3 | 2025-03-29 | — | 1.80% | — |
Full EPSS history (14 records total)
CVSS metrics for this CVE.
| Base score | Version | Severity | Vector | Exploitability | Impact | Score source |
|---|---|---|---|---|---|---|
| 7.5 | 3.1 | HIGH |
|
3.9 | 3.6 | [email protected] |
| 7.5 | 3.1 | HIGH |
|
3.9 | 3.6 | [email protected] |
| 5.0 | 2.0 | MEDIUM |
|
10.0 | 2.9 | [email protected] |
GHSA-wmg4-8cp2-hpg9 · Severity: high · Ecosystem: pip — Sydent vulnerable to denial of service attack via memory exhaustion
| URL | Tags |
|---|---|
| https://github.com/matrix-org/sydent/commit/0523511d2fb40f2738f8a8549868f44b96e5dab7 | Patch Third Party Advisory |
| https://github.com/matrix-org/sydent/commit/89071a1a754c69a50deac89e6bb74002d4cda19d | Patch Third Party Advisory |
| https://github.com/matrix-org/sydent/commit/f56eee315b6c44fdd9f6aa785cc2ec744a594428 | Patch Third Party Advisory |
| https://github.com/matrix-org/sydent/releases/tag/v2.3.0 | Release Notes Third Party Advisory |
| https://github.com/matrix-org/sydent/security/advisories/GHSA-wmg4-8cp2-hpg9 | Patch Third Party Advisory |
| https://pypi.org/project/matrix-sydent/ | Product Third Party Advisory |