# 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.

- **Severity:** High 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 20 Mar 2026
- **Updated:** 20 Mar 2026
- **Also known as:** GHSA-p9hg-pq3q-v9gv, GO-2026-4763, ROOT-OS-UBUNTU-2204-CVE-2026-33191

## 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.

Weakness: CWE-248 (Uncaught Exception), CWE-158 (Improper Neutralization of Null Byte or NUL Character)

## 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 | Ecosystem | 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: Free5gc Udm.

## How do I fix CVE-2026-33191?

Upgrade github.com/free5gc/udm to 1.4.2 or later.

## 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](https://insights.sbomify.com/CVE-2026-33064/): free5GC UDM DataChangeNotification Procedure Panic Due to Nil Pointer Dereference (high 8.7)
- [CVE-2026-33192](https://insights.sbomify.com/CVE-2026-33192/): free5GC UDM incorrectly returns 500 for empty supi path parameter in PATCH sdm-subscriptions reques (high 8.7)
- [CVE-2023-46324](https://insights.sbomify.com/CVE-2023-46324/): free5GC udm vulnerable to Invalid Curve Attack (high 7.5)
- [CVE-2026-33065](https://insights.sbomify.com/CVE-2026-33065/): free5GC UDM incorrectly returns 500 for empty supi path parameter in DELETE sdm-subscriptions request (medium 6.9)
- [CVE-2026-27642](https://insights.sbomify.com/CVE-2026-27642/): free5GC has Improper Input Validation in UDM UEAU Service (medium 6.6)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-33191 and fix it if it is affected.

What it is: 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.
Exploitation: There is no known exploitation of CVE-2026-33191 in the wild and no public exploit code.

Affected packages and fixed versions:
- github.com/free5gc/udm (Go): affected all versions; fixed in 1.4.2
- github.com/free5gc/udm (Go): affected all versions; fixed in 1.4.2
- github.com/free5gc/udm (Go): affected all versions; fixed in 1.4.2

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-33191/ (Markdown: https://insights.sbomify.com/CVE-2026-33191/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33191
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33191
- OSV: https://osv.dev/vulnerability/CVE-2026-33191

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-33191/
Summaries are generated and may contain mistakes; the official description above is the record.