GHSA-c4cm-r9fh-jgj9
commonground-api-common unexploitable privilege escalation in JWT authentication middleware
GHSA-c4cm-r9fh-jgj9 is a vulnerability with no CVSS score yet in commonground-api-common, published February 9, 2024. No source lists public exploit code. No source names a fixed version.
- Severity
- UnratedNo CVSS score yet
- Exploit chance
- UnscoredNo EPSS score yet
- Exploitation
- None knownNot on CISA’s or ENISA’s lists
- Fixed in
- No fix listedNo source names one
Description
Impact
This is a privilege escalation vulnerability. The impact is negligible and entirely theoretical.
A non-exploitable weakness was found in how the client-supplied JWTs are verified. Because an explicit allow-list of known algorithms is used in the PyJWT library, user-supplied (invalid) algorithms are rejected.
If this was not the case, then the client JWTs could be tampered with, resulting in privilege escalation which would allow the attacker to perform any operation as any client (impersonation) without leaving a trace of the real user/client.
Patches
Will be fixed in 1.12.2
Workarounds
None needed. But be careful when updating PyJWT. Check that the used PyJWT has no algorithms specified with a name in "", "HS25", "HS2", "HS", "H", or that those algorithms are acceptable.
Details
The header and payload of JSON Web Tokens (JWTs) are cryptographically signed with an algorithm. A JWT has a header field alg that specifies the algorithm used in the signature.
The vng-api-common.middleware.AuthMiddleware uses PyJWT to check the validity of JWT and indicates it should be "HS256", otherwise an attacker could construct a token with a cryptographically weak token. It should indicate this with a list of acceptable algorithms ["HS256"], but instead the string "HS256" is passed to PyJWT. PyJWT does not check the type of the argument and checks if the alg string in the header exists in the acceptable algorithms value with the in operator. Any substring of "HS256" passes this in check. It is not exploitable because there is no such substring in de set of algorithms PyJWT supports.
Affected packages
| Package | Affected | Fixed |
|---|---|---|
commonground-api-commonPyPI | through 1.12.1 | None known |
vng-api-commonPyPI | through 2.0.5 | None known |
vng-api-common-utrechtPyPI | through 1.3.2 | None known |
commonground-api-commonPyPI | through 1.12.1, plus listed versions 1.10.01.10.11.10.21.11.01.12.01.9.0 | None known |
vng-api-commonPyPI | through 2.0.5, plus listed versions 0.30.00.31.00.31.10.31.20.32.0 Show 45 moreShow less0.32.10.32.20.32.30.33.00.34.00.34.10.35.00.35.10.35.100.35.20.35.30.35.40.35.50.35.60.35.70.35.80.35.90.36.00.36.10.37.00.37.10.37.20.37.30.37.40.38.00.38.10.38.20.39.00.39.10.40.00.40.10.41.00.41.10.41.20.42.00.42.10.43.00.43.10.43.20.43.30.44.00.45.00.46.00.46.10.46.2 | None known |
What each source reports
GitHub AdvisoriesNo score
commonground-api-common unexploitable privilege escalation in JWT authentication middleware
Impact
This is a privilege escalation vulnerability. The impact is negligible and entirely theoretical.
A non-exploitable weakness was found in how the client-supplied JWTs are verified. Because an explicit allow-list of known algorithms is used in the PyJWT library, user-supplied (invalid) algorithms are rejected.
If this was not the case, then the client JWTs could be tampered with, resulting in privilege escalation which would allow the attacker to perform any operation as any client (impersonation) without leaving a trace of the real user/client.
Patches
Will be fixed in 1.12.2
Workarounds
None needed. But be careful when updating PyJWT. Check that the used PyJWT has no algorithms specified with a name in "", "HS25", "HS2", "HS", "H", or that those algorithms are acceptable.
Details
The header and payload of JSON Web Tokens (JWTs) are cryptographically signed with an algorithm. A JWT has a header field alg that specifies the algorithm used in the signature.
The vng-api-common.middleware.AuthMiddleware uses PyJWT to check the validity of JWT and indicates it should be "HS256", otherwise an attacker could construct a token with a cryptographically weak token. It should indicate this with a list of acceptable algorithms ["HS256"], but instead the string "HS256" is passed to PyJWT. PyJWT does not check the type of the argument and checks if the alg string in the header exists in the acceptable algorithms value with the in operator. Any substring of "HS256" passes this in check. It is not exploitable because there is no such substring in de set of algorithms PyJWT supports.
- Record
GHSA-c4cm-r9fh-jgj9- Updated
- 2026-11-02
OSVNo score
commonground-api-common unexploitable privilege escalation in JWT authentication middleware
Impact
This is a privilege escalation vulnerability. The impact is negligible and entirely theoretical.
A non-exploitable weakness was found in how the client-supplied JWTs are verified. Because an explicit allow-list of known algorithms is used in the PyJWT library, user-supplied (invalid) algorithms are rejected.
If this was not the case, then the client JWTs could be tampered with, resulting in privilege escalation which would allow the attacker to perform any operation as any client (impersonation) without leaving a trace of the real user/client.
Patches
Will be fixed in 1.12.2
Workarounds
None needed. But be careful when updating PyJWT. Check that the used PyJWT has no algorithms specified with a name in "", "HS25", "HS2", "HS", "H", or that those algorithms are acceptable.
Details
The header and payload of JSON Web Tokens (JWTs) are cryptographically signed with an algorithm. A JWT has a header field alg that specifies the algorithm used in the signature.
The vng-api-common.middleware.AuthMiddleware uses PyJWT to check the validity of JWT and indicates it should be "HS256", otherwise an attacker could construct a token with a cryptographically weak token. It should indicate this with a list of acceptable algorithms ["HS256"], but instead the string "HS256" is passed to PyJWT. PyJWT does not check the type of the argument and checks if the alg string in the header exists in the acceptable algorithms value with the in operator. Any substring of "HS256" passes this in check. It is not exploitable because there is no such substring in de set of algorithms PyJWT supports.
- Record
GHSA-c4cm-r9fh-jgj9- Updated
- 2026-11-02
History
| Recorded | Changed | Sources |
|---|---|---|
| first indexed | GitHub Advisories, OSV |
Dates are when Every CVE recorded each change. Upstream dates may differ.
References
Left out here: 157 versions. The JSON record has them.