SSRF in Sydent due to missing validation of hostnames
Key facts
- Attack vector
- Network
- Privileges required
- Low
- User interaction
- None
- Attack complexity
- Low
- Impact type
- Information disclosure
- Confidentiality · integrity · availability
- High · None · None
- Fix status
- Fixed
Attack profile from CVSS 3.1 · CNA. Fix status from CNA and GitHub. Impact type from CWE-918 and the CVSS impact.
Summary
Sydent is a reference Matrix identity server. Sydent can be induced to send HTTP GET requests to internal systems, due to lack of parameter validation or IP address blacklisting. It is not possible to exfiltrate data or control request headers, but it might be possible to use the attack to perform an internal port enumeration. This issue has been addressed in in 9e57334, 8936925, 3d531ed, 0f00412. A potential workaround would be to use a firewall to ensure that Sydent cannot reach internal HTTP resources.
Why it matters now
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 | before 2.3.0 | 2.3.0 | Patch available | CNA |
| — | matrix-sydent (PyPI) | before 2.3.0 | 2.3.0 | Patch available | GHSA-9jhm-8m8c-c3f4 |
- sydent Vendormatrix-org Affected before 2.3.0 Fixed in 2.3.0 Patch available CNA
- matrix-sydent (PyPI) Vendor— Affected before 2.3.0 Fixed in 2.3.0 Patch available GHSA-9jhm-8m8c-c3f4
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 · CNA sydent (matrix-org) Fixed in 2.3.0
- Fix · GHSA-9jhm-8m8c-c3f4 matrix-sydent (PyPI) Fixed in 2.3.0 Advisory →
Timeline
- 2026-10-02 Threatist record created from CVE-2021-29431
- 2026-10-03 Alias added: GHSA-9jhm-8m8c-c3f4
References
Patch 5
- https://github.com/matrix-org/sydent/security/advisories/GHSA-9jhm-8m8c-c3f4
- https://github.com/matrix-org/sydent/commit/9e573348d81df8191bbe8c266c01999c9d57cd5f
- https://github.com/matrix-org/sydent/commit/8936925f561b0c352c2fa922d5097d7245aad00a
- https://github.com/matrix-org/sydent/commit/3d531ed50d2fd41ac387f36d44d3fb2c62dd22d3
- https://github.com/matrix-org/sydent/commit/0f00412017f25619bc36c264b29ea96808bf310a
Advisory 3
More matrix-org Sydent vulnerabilities
- TI-2023-20035 Sydent does not verify email server certificates CVSS 3.1CRITICAL 9.3
- 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
- TI-2021-10146 Denial of service (via resource exhaustion) due to improper input validation CVSS 3.1MEDIUM 4.3
Sources
- CVE-2021-29431 · CVE Program
- CVE-2021-29431 · NVD
- FIRST EPSS
- GHSA-9jhm-8m8c-c3f4 · GitHub Advisory Database · CC BY 4.0
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