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🛡️ CVE-2026-33191 — udm

🟠 CVSS 8.6 — High ✅ No Known Exploit CWE-158 NVD
8.6
CVSS Score
0 Low4 Medium7 High9 Critical10

Description

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

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.

How this vulnerability can be exploited

This issue can be reached over the network, attack complexity is low, an attacker needs no privileges on the target. No user interaction is required. The scope is changed, meaning a successful attack can affect components beyond the vulnerable one. Rated impact: confidentiality none, integrity none, availability high.

CVSS metrics in full

The score comes from this vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

  • Attack vector: Network — reachable from anywhere that can route to the service.
  • Attack complexity: Low — the attack works reliably, with no preparation.
  • Privileges required: None — an unauthenticated stranger can try it.
  • User interaction: None — nobody has to be tricked into anything.
  • Scope: Changed — a successful attack reaches components beyond the vulnerable one.
  • Confidentiality impact: None.
  • Integrity impact: None.
  • Availability impact: High — total loss, or loss the attacker controls.

Weakness class

CVE-2026-33191 is classified as 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.

Affected software

CVE-2026-33191 is recorded against 2 packages.

  • github.com/free5gc/udm
  • udm (fixed in 1.4.2)

Timeline and source

Published on 18 March 2026 and last revised on 23 March 2026. No public exploit is currently recorded for this entry. A vendor advisory or fix has been published. Record sourced from NVD.

References

github.com (Web)
nvd.nist.gov (Advisory)
github.com (Web)
github.com (Web)
github.com (Package)

Other advisories for this package

github.com/free5gc/udm has other advisories on record. If you are patching this one, these are worth checking on the same host:

Same weakness in other software

These advisories are the same class of weakness (CWE-158: Improper Neutralization of Null Byte or NUL Character) in other software:

CVE-2026-33191 on other distributions

Each distribution ships its own build and its own fixed version. Pick the one you run:

Details

Severity HIGH
CVSS Score 8.6
CVSS Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H
CWE CWE-158
Public Exploit ✅ No
Source NVD
Published 2026-03-18
Updated 2026-08-20
Modified 2026-03-23

Affected Packages

Software From version Fixed in
github.com/free5gc/udm — —
udm — 1.4.2

Similar Threats

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ⓘ Data Notice: The information presented above has been compiled from publicly available internet sources. Boteraser aggregates this data solely for informational purposes and does not independently classify, evaluate, or endorse any findings about the vulnerabilities listed. The accuracy and completeness of this information is the sole responsibility of the original publishers. Boteraser and its operators accept no liability for any decisions made based on this data.

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