CVE-2021-29431
SSRF in Sydent due to missing validation of hostnames
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.
Attack profile
How easy it is to exploit
- Attack vector
- Network
- Complexity
- Low
- Privileges needed
- Low
- User interaction
- None
What an attacker can affect
- Confidentiality
- High
- Integrity
- None
- Availability
- None
Exploit likelihood
What each source reports
CVE List Score used
SSRF in Sydent due to missing validation of hostnames
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.
- Record
CVE-2021-29431- CVSS 3.1
- 7.7 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-20, CWE-918
- Updated
- 2026-11-02
EUVDEUVD-2021-0120
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.
- Record
EUVD-2021-0120- CVSS 3.1
- 7.7 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N - Updated
- 2026-11-03
GitHub AdvisoriesGHSA-9jhm-8m8c-c3f4
SSRF in Sydent due to missing validation of hostnames
Impact
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.
Patches
Fixed in 9e57334, 8936925, 3d531ed, 0f00412
Workarounds
A potential workaround would be to use a firewall to ensure that Sydent cannot reach internal HTTP resources.
For more information
If you have any questions or comments about this advisory, email us at [email protected].
- Record
GHSA-9jhm-8m8c-c3f4- CVSS 4.0
- 6.3 Medium
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N - CVSS 3.1
- 7.7 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-20, CWE-918
- Updated
- 2026-11-02
NVD
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.
- Record
CVE-2021-29431- CVSS 3.1
- 7.7 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N - CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - CVSS 2.0
- 4.0 Medium
AV:N/AC:L/Au:S/C:P/I:N/A:N - Weakness
- CWE-20, CWE-918
- Updated
- 2026-11-02
OSV
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.
- Record
CVE-2021-29431- CVSS 3.1
- 6.5 Medium
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N - Updated
- 2026-11-02
OSVGHSA-9jhm-8m8c-c3f4
SSRF in Sydent due to missing validation of hostnames
Impact
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.
Patches
Fixed in 9e57334, 8936925, 3d531ed, 0f00412
Workarounds
A potential workaround would be to use a firewall to ensure that Sydent cannot reach internal HTTP resources.
For more information
If you have any questions or comments about this advisory, email us at [email protected].
- Record
GHSA-9jhm-8m8c-c3f4- CVSS 4.0
- 6.3 Medium
CVSS:4.0/AV:N/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:N/SC:H/SI:N/SA:N - CVSS 3.1
- 7.7 High
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:N/A:N - Weakness
- CWE-20, CWE-918
- Updated
- 2026-11-02
OSVPYSEC-2021-22 No score
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.
- Record
PYSEC-2021-22- Updated
- 2026-11-02
Affected products
Affected packages
| Package | Affected | Fixed |
|---|---|---|
matrix-sydentPyPI |
before 2.3.0 | 2.3.0 |
matrix-sydentPyPI |
before 2.3.0, plus listed versions 2.0.02.0.12.1.02.2.0 |
2.3.0 |
History
| Recorded | Changed | Sources |
|---|---|---|
| aliases | EUVD | |
| first indexed | CVE List, GitHub Advisories, NVD, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
In short
CVE-2021-29431 is a high vulnerability (CVSS 7.7) in Matrix Sydent, published April 15, 2021. No source lists public exploit code. EPSS puts the chance of exploitation in the next 30 days at 1.19%, the 68th percentile. Fixed in matrix-sydent 2.3.0.
References
pypi.org/project/matrix-sydent
github.com/matrix-org/sydent/releases/tag/v2.3.0