Denial of service (via resource exhaustion) due to improper input validation
Priority LOW 22CWE-20Published · Updated
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Denial of service
- Confidentiality · integrity · availability
- None · None · Low
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-400.
Summary
Sydent is a reference Matrix identity server. In Sydent versions 2.2.0 and prior, sissing input validation of some parameters on the endpoints used to confirm third-party identifiers could cause excessive use of disk space and memory leading to resource exhaustion. A patch for the vulnerability is in version 2.3.0. No workarounds are known to exist.
Why it matters now
EPSS 0.00927 60th percentileScored 2026-11-07
Fix Fixed matrix-sydent (PyPI): 2.3.0
SSVC decision points
Not available: CISA has not published SSVC decision points for this record.
Affected products
| Vendor | Product | Affected versions | Fixed in | Status | Source |
|---|---|---|---|---|---|
| matrix-org | sydent | up to 2.2.0 | — | No fix listed | CNA |
| — | matrix-sydent (PyPI) | before 2.3.0 | 2.3.0 | Patch available | GHSA-pw4v-gr34-2553 |
- sydent Vendormatrix-org Affected up to 2.2.0 Fixed in — No fix listed CNA
- matrix-sydent (PyPI) Vendor— Affected before 2.3.0 Fixed in 2.3.0 Patch available GHSA-pw4v-gr34-2553
CPE configurations NVD · 1
| CPE | Versions | Role | Vendor |
|---|---|---|---|
| cpe:2.3:a:matrix:sydent:*:*:*:*:*:*:*:* | before 2.3.0 | Vulnerable | matrix-org |
- cpe:2.3:a:matrix:sydent:*:*:*:*:*:*:*:* Versions before 2.3.0 Vulnerable ·matrix-org
Remediation
- Fix · GHSA-pw4v-gr34-2553 matrix-sydent (PyPI) Fixed in 2.3.0 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2021-29433
- 2026-10-03 Alias added: GHSA-pw4v-gr34-2553
References
Patch 2
More matrix-org Sydent vulnerabilities
- TI-2023-20035 Sydent does not verify email server certificates CVSS 3.1CRITICAL 9.3
- TI-2021-10144 SSRF in Sydent due to missing validation of hostnames CVSS 3.1HIGH 7.7
- TI-2021-10143 Denial of service attack via memory exhaustion CVSS 3.1HIGH 7.5
- TI-2019-08878 An issue was discovered in Matrix Sydent before 1.0.3 and Synapse before 0.99.3.1. CVSS 3.0HIGH 7.5
- TI-2019-08469 util/emailutils.py in Matrix Sydent before 1.0.2 mishandles registration restrictions… CVSS 3.0MEDIUM 5.9
- TI-2021-10145 Malicious users could control the content of invitation emails CVSS 3.1MEDIUM 5.7
Sources
- CVE-2021-29433 · CVE Program
- CVE-2021-29433 · NVD
- FIRST EPSS
- GHSA-pw4v-gr34-2553 · GitHub Advisory Database · CC BY 4.0
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