CVE-2026-44320 is a high-severity (CVSS 7.3) Missing Authentication vulnerability in github.com/free5gc/nef. No vendor fix is recorded yet; mitigation options are listed below.
free5GC: NEF nnef-callback route group is unauthenticated; forged callback requests are accepted into the processing path
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-2026-44320.
EPSS Exploitation Probability
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.
How urgent is this, really
CVE-2026-44320 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 378,156 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
github.com/free5gc/nefReal-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
Summary
free5GC's NEF mounts the nnef-callback route group without inbound OAuth2/bearer-token authorization. A forged or arbitrary bearer token (e.g. Authorization: Bearer not-a-real-token) is enough to reach the SMF-callback handler -- the callback body is parsed and dispatched into NEF business logic instead of being rejected at the auth boundary. Same root cause as the other NEF SBI findings: the route group is mounted without any inbound auth middleware. NEF does not authenticate the producer NF identity before processing callback content; if an attacker can guess or obtain a valid NotifId, this missing auth boundary lets forged callbacks act on real subscription state. The route group is also reachable even when the runtime ServiceList does not declare it (it lists only nnef-pfdmanagement and nnef-oam).
Details
Validated against the NEF container in the official Docker compose lab.
- Running Docker image:
free5gc/nef:v4.2.1 - Docker validation date: 2026-03-11
NEF advertises OAuth2 setting receive from NRF: true, yet the nnef-callback route group is mounted with no inbound auth middleware. The API layer reads the raw request body and deserializes it before any auth check, then the processor looks up subscription state by NotifId.
Code evidence (paths in free5gc/nef):
- Callback route group mounted without auth middleware:
NFs/nef/internal/sbi/server.go:64 - Callback route exposed at
/notification/smf:NFs/nef/internal/sbi/api_callback.go:13 - API layer reads raw request bytes and deserializes them before any auth check:
NFs/nef/internal/sbi/api_callback.go:23 - Processor looks up the subscription by
NotifId:NFs/nef/internal/sbi/processor/callback.go:13 - NEF context only exposes outbound token acquisition (
GetTokenCtx); there is no inbound authorization path:NFs/nef/internal/context/nef_context.go:153 - Config validation only allows
nnef-pfdmanagementandnnef-oam:NFs/nef/pkg/factory/config.go:126
PoC
Reproduced against the running NEF at http://10.100.200.19:8000 using a fabricated bearer token.
Send a forged callback request:
curl -i \
-H 'Authorization: Bearer not-a-real-token' \
-H 'Content-Type: application/json' \
--data '{"notifId":"forged-notif","eventNotifs":[]}' \
http://10.100.200.19:8000/nnef-callback/v1/notification/smf
Observed output:
HTTP/1.1 404 Not Found
{"title":"Data not found","status":404,"detail":"Subscription is not found"}
The 404 is positive auth-bypass evidence: the request was parsed and dispatched into the callback business handler instead of being rejected at the auth boundary. NEF container logs (docker logs nef) confirm the callback handler was reached:
[INFO][NEF][TraffInfl] SmfNotification - NotifId[forged-notif]
[INFO][NEF][GIN] | 404 | POST | /nnef-callback/v1/notification/smf
Impact
Missing inbound authentication (CWE-306) and authorization (CWE-862) on the NEF nnef-callback SBI route group. This is the trusted ingestion point for SMF -> NEF notifications. The defect is route-group-scoped: there is no auth middleware on the group at all, so every callback endpoint inside this group inherits the missing inbound auth boundary. Severity is scored against the route group's intended capability surface (consume SMF notifications and mutate NEF / downstream subscription state), NOT against the specific PoC where the chosen NotifId happened to be invalid.
Any party that can reach NEF on the SBI can:
- Submit forged SMF callbacks to NEF anonymously, with body content fully controlled by the attacker.
- Reach NEF callback business logic without proving producer NF identity, so any attacker who can guess or obtain a valid
NotifIdcan deliver forged event notifications against real subscription state -- corrupting AF traffic-influence / PFD-management subscription views and the downstream SMF/UPF policy decisions that depend on them. - Hit any future callback added behind this same route group anonymously, because the auth boundary does not exist for this group.
The nnef-callback route group is also reachable even when the runtime ServiceList does not declare it, so operators relying on ServiceList to disable the service do not actually get that protection.
Affected: free5gc v4.2.1.
Upstream issue: https://github.com/free5gc/free5gc/issues/860 Upstream fix: https://github.com/free5gc/nef/pull/24
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐹Go | github.com/free5gc/nef | all versions | No fix |
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/free5gc/nef, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Remediation status
No patched version of github.com/free5gc/nef has shipped for CVE-2026-44320 yet. Where your build allows, override or pin the dependency away from the vulnerable range, and apply any maintainer-recommended mitigation.
Mitigate without a patch
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-2026-44320 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2026-44320. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Frequently Asked Questions
Is CVE-2026-44320 in your dependencies?
O3 Security finds CVE-2026-44320 across Go dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.