CVE-2026-33191 free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error
Remote attackers can cause denial of service in free5GC UDM by injecting null bytes into URL path parameters, triggering internal server errors.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-33191?
CVE-2026-33191 is a high-severity denial of service vulnerability in free5gc, published on 20 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
Free5GC is an open-source Linux Foundation project for 5th generation (5G) mobile core networks. Versions prior to 1.4.2 are vulnerable to null byte injection in URL path parameters. 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. 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. This issue has been fixed in version 1.4.2.
Which versions are affected by CVE-2026-33191?
3 open source packages ship an affected version, including github.com/free5gc/udm. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/free5gc/udm Go | All versions | 1.4.2 |
github.com/free5gc/udm Go | All versions | 1.4.2 |
github.com/free5gc/udm Go | All versions | 1.4.2 |
Products include Free5gc Udm.
How do I fix CVE-2026-33191?
Upgrade github.com/free5gc/udm to 1.4.2 or later.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-33191 being exploited?
There is no known exploitation of CVE-2026-33191 in the wild and no public exploit code.
Other vulnerabilities in free5gc
- CVE-2026-33064 free5GC UDM DataChangeNotification Procedure Panic Due to Nil Pointer Dereference
- CVE-2026-33192 free5GC UDM incorrectly returns 500 for empty supi path parameter in PATCH sdm-subscriptions reques
- CVE-2023-46324 free5GC udm vulnerable to Invalid Curve Attack
- CVE-2026-33065 free5GC UDM incorrectly returns 500 for empty supi path parameter in DELETE sdm-subscriptions request
- CVE-2026-27642 free5GC has Improper Input Validation in UDM UEAU Service
Sources
Also known as GHSA-p9hg-pq3q-v9gv, GO-2026-4763, ROOT-OS-UBUNTU-2204-CVE-2026-33191.