CVE-2026-44329: free5GC's SMF UPI management interface lacks auth middleware; unauthenticated topology read/write requests reach handlers

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• Not in CISA KEV, but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
• EPSS 0.6%, percentile 46: FIRST’s model estimates a 0.6% chance of exploitation activity in the next 30 days, higher than 46% of all scored CVEs (low). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/free5gc/smf (Go) < 1.4.3, fixed in 1.4.3. Check your lockfile, including transitive dependencies.

What it is

free5GC is an open-source implementation of the 5G core network. Prior to 4.2.2, free5GC's SMF mounts the UPI management route group without OAuth2/bearer-token authorization middleware. A network attacker who can reach SMF on the SBI can hit UPI endpoints with no Authorization header at all, and the requests reach the SMF business handlers. In the running Docker lab this was directly demonstrated for read (GET /upi/v1/upNodesLinks), write (POST /upi/v1/upNodesLinks with attacker-controlled UP-node and link payload), and delete (DELETE /upi/v1/upNodesLinks/{nodeID}) operations. This vulnerability is fixed in 4.2.2.

From the GitHub advisory

Summary free5GC's SMF mounts the UPI management route group without OAuth2/bearer-token authorization middleware. A network attacker who can reach SMF on the SBI can hit UPI endpoints with no Authorization header at all, and the requests reach the SMF business handlers. In the running Docker lab this was directly demonstrated for read (GET /upi/v1/upNodesLinks), write (POST /upi/v1/upNodesLinks with attacker-controlled UP-node and link payload), and delete (DELETE /upi/v1/upNodesLinks/{nodeID}) operations.

The defect is route-group-scoped: there is no inbound auth middleware on the UPI group at all, while a control comparison against the sibling nsmf-oam group on the same SMF instance shows OAM IS protected (no-token request returns 401 Unauthorized). So this is not a global config gap -- it is specifically that the UPI group was mounted without the auth middleware that the OAM group has.

Details Validated against the SMF container in the official Docker compose lab. - Source repo tag: v4.2.1 - Running Docker image: free5gc/smf:v4.2.0 - Docker validation date: 2026-03-13

Control comparison on the same SMF instance: - GET /upi/v1/upNodesLinks (no token) -> 200 OK - GET /nsmf-oam/v1/ (no token) -> 401 Unauthorized

This side-by-side proves OAuth2 middleware is wired in for nsmf-oam but not for UPI on the same process.

Weakness type: CWE-306, CWE-862.

Product: github.com/free5gc/smf (Go) · Assigned by: GitHub_M · Published: 2026-05-27

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: changed (can affect other components)

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation poc, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.56% probability of exploitation activity in the next 30 days; percentile 46.

Timeline

• 2026-05-08 — GitHub-reviewed advisory GHSA-3258-qmv8-frp3 published (critical)
• 2026-05-27 — CVE record published by GitHub_M
• 2026-05-28 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-3258-qmv8-frp3 github.com
2. CVE.org record CVE-2026-44329 cve.org
3. NVD entry CVE-2026-44329 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com
3. github.com github.com
4. github.com github.com

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