---
id: CVE-2026-53551
title: free5GC is an open-source implementation of the 5G core network
summary: >-
  free5GC is an open-source implementation of the 5G core network. Prior to
  1.4.5, the free5GC AUSF (Authentication Server Function) does not validate the
  supiOrSuci field in UE authentication requests. Null bytes (\x00) and other
  control …
severity: medium
cwe:
  - CWE-20
vendor: free5gc
product: github.com/free5gc/free5gc
affected:
  - github.com/free5gc/free5gc < 4.2.2
  - github.com/free5gc/ausf < 1.4.5
patched:
  - github.com/free5gc/free5gc 4.2.2
  - github.com/free5gc/ausf 1.4.5
published: '2026-07-31'
updated: '2026-09-08'
sourceUpdated: '2026-09-08T20:51:43.490'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-53551'
references:
  - url: >-
      https://github.com/free5gc/ausf/commit/bfc4a10094dbacbd862baa4686829f3fcc06ce1e
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/ausf/pull/61'
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/ausf/releases/tag/v1.4.5'
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/free5gc/issues/1048'
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/free5gc/releases/tag/v4.2.2'
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/free5gc/security/advisories/GHSA-qj55-47fp-p62j'
    label: security-advisories@github.com
  - url: 'https://github.com/free5gc/free5gc/security/advisories/GHSA-qj55-47fp-p62j'
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: 'https://github.com/advisories/GHSA-qj55-47fp-p62j'
tags:
  - nvd
  - ghsa
  - go
epss: 0.00737
epssPercentile: 0.52548
aliases:
  - GHSA-qj55-47fp-p62j
ecosystem: go
ingestedAt: '2026-07-31T21:03:50.464Z'
---

## Overview

free5GC is an open-source implementation of the 5G core network. Prior to 1.4.5, the free5GC AUSF (Authentication Server Function) does not validate the supiOrSuci field in UE authentication requests. Null bytes (\x00) and other control characters pass through JSON parsing unchanged and are forwarded to the UDM in an unescaped URL path. This causes Go's net/url.Parse() to fail, returning HTTP 500 "System failure" and leaking internal stack traces. An unauthenticated attacker can trigger this at scale causing denial of service for all subscribers attempting authentication through the affected AUSF. This vulnerability is fixed in 1.4.5.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Package advisory (CVE-2026-53551)

Affected packages:

- `github.com/free5gc/free5gc < 4.2.2`
- `github.com/free5gc/ausf < 1.4.5`

Patched in:

- `github.com/free5gc/free5gc 4.2.2`
- `github.com/free5gc/ausf 1.4.5`

Source: https://github.com/advisories/GHSA-qj55-47fp-p62j