How severe is CVE-2026-33191?

No CVSS score has been assigned to CVE-2026-33191 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-33191?

CVE-2026-33191 affects the following packages: github.com/free5gc/udm (Go). Ecosystems affected: Go.

How do I fix CVE-2026-33191?

Update github.com/free5gc/udm to 1.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33191 is resolved across your whole dependency graph.

How do I detect CVE-2026-33191 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/free5gc/udm, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-33191 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-33191?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33191 can be triaged on real exposure rather than presence alone.

Is CVE-2026-33191 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-33191 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-33191?

CVE-2026-33191 has an EPSS (Exploit Prediction Scoring System) score of 0.4%, placing it in the 29th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-33191?

CVE-2026-33191 is classified as CWE-158 (CWE-158), CWE-248 (CWE-248). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2026-33191 published, and has it been updated?

CVE-2026-33191 was published on March 20, 2026 and was last updated on August 12, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹 Go

Not in CISA KEV

CVE-2026-33191 — udm

Fix: free5gc/udm@88de9fa

CVE-2026-33191 is a CWE-158 vulnerability in github.com/free5gc/udm. A fix is available for github.com/free5gc/udm — see the affected versions and patch details below.

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

Also known asGHSA-p9hg-pq3q-v9gvGO-2026-4763

Published

Mar 20, 2026

Updated

Aug 12, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 22, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

CISA assesses this as automatable — exploitation doesn’t require manual, per-target effort, which raises the odds of mass scanning and opportunistic attacks.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-33191.

EPSS Exploitation Probability

via FIRST.org ↗

0.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs29th percentile — riskier than 29% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Real-World Exposure

1 pkg affected

🐹github.com/free5gc/udm

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/free5gc/udm`	all versions	1.4.2`go get github.com/free5gc/udm@v1.4.2`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/free5gc/udm, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/free5gc/udm to 1.4.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-33191 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-33191 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-33191. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

**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, t

O3 Security · Impact-Aware SCA

Is CVE-2026-33191 in your dependencies?

O3 Security finds CVE-2026-33191 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works