High

CVE-2026-33191 — free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error

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.

Published Mar 20, 2026 · Updated Oct 13, 2026 · Sources: NIST National Vulnerability Database, CVE Program (cve.org) e CISA ADP · CNA: GitHub_M

Low

Who exploits it and how urgent it is

A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.

No exploitation signal in the sources consulted so far.

How the score was calculated

EPSS 0.6% (30-day exploitation probability)+7
Technical severity (high)+6
Automatable exploitation (SSVC)+3

The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.

Exploitation

Not confirmed

Not in CISA KEV — an absence of record, not proof it is unexploited.

EPSS FIRST

0.58%

ahead of 46% of scored CVEs · Oct 14, 2026

Affects

Free5gc

Free5gc and 1 more

CVSS base

8.6

High · 3 source(s)

CISA SSVC assessment CISA

Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.

Exploitation

None

none · proof-of-concept · active

Automatable

Yes

can an attacker script the kill-chain steps

Technical impact

Partial

partial · total control of the vulnerable component

Remediation

Fixes and mitigations documented by the sources — linked to the original advisory.

Documented patch — github.com (NIST National Vulnerability Database)
Documented patch — github.com (NIST National Vulnerability Database)

First 24 hours

Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.

Identify exposed assets running the affected vendor/product/version combinations (Free5gc Free5gc, Free5gc Udm).
The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
Apply the fixed version or the patch documented under Remediation.
Search available logs for exploit probes, errors and authentication anomalies.

Affected scope

Vendor, product and versions as the sources word them.

Vendor	Product	Versions	Status	Source
Free5gc	Free5gc	version < 1.4.2	Vulnerable	CVE Program (cve.org) e CISA ADP
Free5gc	Udm	< 1.4.2	Vulnerable	NIST National Vulnerability Database

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Attack vector

Network

Attack complexity

Low

Privileges required

None

User interaction

None

Scope

Changed

Confidentiality

None

Integrity

None

Availability

High

Every base score collected

Sources score independently and may disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Scored by
8.7	CVSS 4.0	High	—	—	security-advisories@github.com via NIST National Vulnerability Database
8.7	CVSS 4.0	High	—	—	GitHub_M via CVE Program (cve.org) e CISA ADP
8.6	CVSS 3.1	High	3.9	4.0	nvd@nist.gov via NIST National Vulnerability Database

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H (score shown at the top: nvd@nist.gov)

Weakness MITRE

Weakness class according to MITRE’s CWE catalog.

CWE-158

Other CVEs with this weakness →

EPSS over time FIRST

Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.58%

Detection

Read off the CVSS vector and the weakness class. Starting points, not tested rules.

Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).

web/proxy/WAF logsnetwork IDS/IPS

Timeline

What happened to this CVE, newest first.

2026
Affected products added · free5gc/free5gc
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
SSVC assessment updated
Oct 13, 2026 · CVE Program (cve.org) e CISA ADP
Record published
Oct 13, 2026
Fix documented
Oct 13, 2026 · NIST National Vulnerability Database
CVSS changed · 8.6
Oct 13, 2026 · NIST National Vulnerability Database
Source status changed · → Analyzed
Oct 13, 2026 · NIST National Vulnerability Database
Record created in this database
Oct 13, 2026 · NIST National Vulnerability Database
CVE published
Mar 20, 2026 · GitHub_M

Source activity

Repeated readings are counted rather than listed.

1× Official description updated · Oct 13, 2026 – Oct 13, 2026

References

2 on the record

github.com/free5gc/udm/commit/88de9fa74a1b3f3522e53b4cfa2d184712ffa4ee
Patch, x_refsource_MISC, NIST National Vulnerability Database
github.com/free5gc/free5gc/security/advisories/GHSA-p9hg-pq3q-v9gv
Patch, Vendor Advisory, x_refsource_CONFIRM, NIST National Vulnerability Database

Elsewhere on this site

Free5gc
every CVE for this vendor

CWE-158
other pages naming this weakness

Related CVEs (same products)

High CVE-2026-44328 free5GC: SMF UPI DELETE /upi/v1/upNodesLinks/{ref} panics on AN-node deletion via nil UPF dereference; unauthenticated, state-mutating May 27, 2026
Critical CVE-2026-44329 free5GC: SMF UPI management interface lacks auth middleware; unauthenticated topology read/write requests reach handlers May 27, 2026
Critical CVE-2026-44330 free5GC: NEF nnef-pfdmanagement API is unauthenticated; forged bearer tokens can read PFD data and create/delete PFD subscriptions May 27, 2026
Critical CVE-2026-44327 free5GC: NEF nnef-oam route group is unauthenticated; no-token requests reach the OAM handler May 27, 2026
Critical CVE-2026-44326 free5GC: NEF 3gpp-traffic-influence API is unauthenticated; missing or forged bearer tokens can create, read, patch, and delete subscriptions May 27, 2026
High CVE-2026-44322 free5GC: NEF 3gpp-pfd-management PATCH applications/{appId} panics on UDR access failure due to nil ProblemDetails dereference May 27, 2026

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record

Text assembled only from the fields above — no additional claims.

What should defenders know first?

CVE-2026-33191 is "free5GC UDM vulnerable to null byte injection in URL path parameters causing 500 Internal Server Error", rated High. It affects Free5gc (Free5gc); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 8.6 describes technical severity. EPSS 0.58% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.

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