CVE-2026-33191: Github.com/free5gc/udm Free5GC UDM Vulnerable To Null Vulnerability

HIGH
Advisory Identifier: GHSA-p9hg-pq3q-v9gv
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CWE-158 CWE-248
Published
Advisory Summary

CVE-2026-33191 is a HIGH free5gc udm vulnerable to null vulnerability (CWE-158: Improper Neutralization of Null Byte or NUL Character) affecting Github.com/free5gc/udm libraries in the Go ecosystem. The issue involves free5gc udm vulnerable to null byte injection in url path parameters causing 500 internal server error. Remediation is available by upgrading affected packages to version 1.4.2.

CVE-2026-33191 at a Glance

CVE Identifier CVE-2026-33191
GHSA Identifier GHSA-p9hg-pq3q-v9gv
Severity HIGH
CVSS v3.1 Base Score N/A
CWE Classification CWE-158: Improper Neutralization of Null Byte or NUL Character
Affected Product Github.com/free5gc/udm
Package Ecosystem Go
Published Date
Last Updated

How to Fix CVE-2026-33191

To remediate this vulnerability, upgrade all affected Github.com/free5gc/udm dependencies to a patched release. Both direct and transitive dependencies should be checked, as frameworks or security libraries may pull in vulnerable versions transitively.

github.com/free5gc/udm fixed: 1.4.2 
Upgrade github.com/free5gc/udm to 1.4.2
Verify Direct and Transitive Dependencies

Run the following command in your project directory to verify that all resolved dependencies use the patched release: 

inspect dependencies for github.com/free5gc/udm

How to Check if You Are Affected

To determine whether your application is affected by CVE-2026-33191, inspect your project dependencies for Github.com/free5gc/udm:

inspect dependencies for github.com/free5gc/udm

Analyze the terminal output to locate any version of Github.com/free5gc/udm in your dependency tree. If any resolved version matches the vulnerable ranges listed in the table below (for example, versions earlier than 1.4.2), your application is affected.

Note: Verify declared build manifests and deployed runtime container environments.

Technical Details

Vulnerability Mechanism & Technical Analysis

This vulnerability is classified under CWE-158: Improper Neutralization of Null Byte or NUL Character, where the product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes nul characters or null bytes when they are sent to a downstream component. In Github.com/free5gc/udm, software state validation or input boundaries are circumvented during processing. Review the official source advisory statement below for specific affected components, classes, and reproduction details.

Source Advisory Statement

**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.

CVE-2026-33191 Affected Github.com/free5gc/udm Versions

1 component(s)
Fixed Versions:
1.4.2
Product / Package Ecosystem Affected Versions Fixed Version
github.com/free5gc/udm
golang/github.com/free5gc/udm
Go
< 1.4.2
1.4.2

References

GitHub Advisory / Wiki ADVISORY
https://github.com/free5gc/free5gc/security/advisories/GHSA-p9hg-pq3q-v9gv
NVD — CVE-2026-33191 NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-33191
Github.com/free5gc/udm Source Repository REPOSITORY
https://github.com/free5gc/udm/pull/79
Security Fix Commit FIX COMMIT
https://github.com/free5gc/udm/commit/88de9fa74a1b3f3522e53b4cfa2d184712ffa4ee
Github.com/free5gc/udm Source Repository REPOSITORY
https://github.com/free5gc/udm

Frequently Asked Questions

What is CVE-2026-33191?
CVE-2026-33191 is a security vulnerability in Github.com/free5gc/udm involving free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error under CWE-158: Improper Neutralization of Null Byte or NUL Character.
Which Github.com/free5gc/udm versions are affected?
Affected versions include releases prior to 1.4.2 across affected packages: github.com/free5gc/udm.
What version fixes CVE-2026-33191?
Upgrading to 1.4.2 (or the latest patched release for your respective branch) resolves the vulnerability.
Is github.com/free5gc/udm affected?
Yes, github.com/free5gc/udm is affected in releases prior to 1.4.2. Upgrade your dependency to 1.4.2 or later.
What CWE is associated with CVE-2026-33191?
CVE-2026-33191 is classified under CWE-158: Improper Neutralization of Null Byte or NUL Character (The product receives input from an upstream component, but it does not neutralize or incorrectly neutralizes NUL characters or null bytes when they are sent to a downstream component.).
How can I check Go dependencies for CVE-2026-33191?
Run the dependency tree command: 'inspect dependencies for github.com/free5gc/udm'. This command lists direct and transitive dependencies in your build configuration so you can verify if a vulnerable version is resolved.
Machine-readable OSV JSON OSV v1.5 Schema
Normalized schema output
View Raw JSON 
{
  "schema_version" : "1.4.0",
  "id" : "GHSA-p9hg-pq3q-v9gv",
  "modified" : "2026-03-20T21:24:27Z",
  "published" : "2026-03-18T20:11:15Z",
  "aliases" : [ "CVE-2026-33191" ],
  "summary" : "free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error",
  "details" : "**Impact**  \nThis is an Improper Input Validation vulnerability with Denial of Service and Injection implications.  \n- **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.  \n- **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.  \n- **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`).\n\n**Patches**  \nYes, the issue has been patched.  \nThe fix is implemented in PR free5gc/udm#79.  \nUsers should upgrade to the next release of free5GC that includes this commit.\n\n**Workarounds**  \nThere 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.",
  "severity" : [ {
    "type" : "CVSS_V4",
    "score" : "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"
  } ],
  "affected" : [ {
    "package" : {
      "ecosystem" : "Go",
      "name" : "github.com/free5gc/udm"
    },
    "ranges" : [ {
      "type" : "ECOSYSTEM",
      "events" : [ {
        "introduced" : "0"
      }, {
        "fixed" : "1.4.2"
      } ]
    } ]
  } ],
  "references" : [ {
    "type" : "WEB",
    "url" : "https://github.com/free5gc/free5gc/security/advisories/GHSA-p9hg-pq3q-v9gv"
  }, {
    "type" : "ADVISORY",
    "url" : "https://nvd.nist.gov/vuln/detail/CVE-2026-33191"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/free5gc/udm/pull/79"
  }, {
    "type" : "WEB",
    "url" : "https://github.com/free5gc/udm/commit/88de9fa74a1b3f3522e53b4cfa2d184712ffa4ee"
  }, {
    "type" : "PACKAGE",
    "url" : "https://github.com/free5gc/udm"
  } ],
  "database_specific" : {
    "cwe_ids" : [ "CWE-158", "CWE-248" ],
    "severity" : "HIGH",
    "github_reviewed" : true,
    "github_reviewed_at" : "2026-03-18T20:11:15Z",
    "nvd_published_at" : "2026-03-20T08:16:12Z"
  }
}