free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS 4.0

8.7 · CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N · score source

EPSS

• CVE-2026-33191: 0.36% estimated exploitation activity in the next 30 days; percentile 29.89 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 NudmSubscriberDataManagement 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 NudmSDM service with endpoints that include path parameters (e.g., /nudm-sdm/v2/{supi}/am-data). Patches Yes, the issue has been patched.…

Published by the source

18 Mar 2026, 20:11 UTC

Last modified by the source

20 Mar 2026, 21:24 UTC

Source last checked

26 Oct 2026, 15:18 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-p9hg-pq3q-v9gv

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# Patch Next advisory brief: CVE-2026-33191

Advisory: free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error
IDs: CVE-2026-33191, GHSA-p9hg-pq3q-v9gv
Record: https://patchnext.com/advisories/cve-2026-33191 (revision 1, source checked 26 Oct 2026, 15:18 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.7)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/free5gc/udm 1.4.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/free5gc/udm: affected < 1.4.2; fixed in 1.4.2

## Suggested inspection (read-only)
- Go github.com/free5gc/udm: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/free5gc/udm.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-p9hg-pq3q-v9gv (GitHub-reviewed advisory GHSA-p9hg-pq3q-v9gv lists affected ranges: Go github.com/free5gc/udm >=0 <1.4.2)

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