CVE-2026-33191

Impact

**Impact** This is an Improper Input Validation vulnerability with Denial of Service and Injection implications. - **Security Impact**: A remote attacker can inject null bytes (URL-encoded as `%00`) into the `supi` path parameter of the UDM's Nudm_SubscriberDataManagement API. This causes URL parsing failure in Go's `net/url` package with the error "invalid control character in URL", resulting in a 500 Internal Server Error. This null byte injection vulnerability can be exploited for denial of service attacks. - **Functional Impact**: When the `supi` parameter contains null characters, the UDM attempts to construct a URL for UDR that includes these control characters. Go's URL parser rejects them, causing the request to fail with 500 instead of properly validating input and returning 400 Bad Request. - **Affected Parties**: All deployments of free5GC v4.0.1 using the UDM Nudm_SDM service with endpoints that include path parameters (e.g., `/nudm-sdm/v2/{supi}/am-data`). **Patches** Yes, the issue has been patched. The fix is implemented in PR free5gc/udm#79. Users should upgrade to the next release of free5GC that includes this commit. **Workarounds** There is no direct workaround at the application level. The recommendation is to apply the provided patch or implement API gateway-level validation to reject requests containing null bytes in path parameters before they reach UDM.

Affected packages

Affected products

Weakness classification

References

• NVD record
• CVE.org record
• GitHub advisory
• https://github.com/free5gc/free5gc/security/advisories/GHSA-p9hg-pq3q-v9gv
• https://github.com/free5gc/udm/commit/88de9fa74a1b3f3522e53b4cfa2d184712ffa4ee
• https://github.com/advisories/GHSA-p9hg-pq3q-v9gv
• https://github.com/free5gc/udm/pull/79
• https://nvd.nist.gov/vuln/detail/CVE-2026-33191