CVE-2026-33063 in Free5GC
Summary
by MITRE • 03/20/2026
free5GC is an open source 5G core network. free5GC AUSF prior to version 1.4.2 has is an Improper Null Check vulnerability leading to Denial of Service. All deployments of free5GC v4.0.1 using the AUSF UE authentication service (`/nausf-auth/v1/ue-authentications` endpoint) are affected. A remote attacker can cause the AUSF service to panic and crash by sending a crafted UE authentication request that triggers a nil interface conversion in the `GetSupiFromSuciSupiMap` function. This results in complete denial of service for the AUSF authentication service. The `GetSupiFromSuciSupiMap` function attempts to perform an interface conversion from `interface{}` to `*context.SuciSupiMap` without checking if the underlying value is nil. When `SuciSupiMap` is nil, the code panics with "interface conversion: interface {} is nil, not *context.SuciSupiMap". free5GC AUSF version 1.4.2 patches the issue. There is no direct workaround at the application level. The recommendation is to apply the provided patch or restrict access to the AUSF API to trusted sources only.
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Analysis
by VulDB Data Team • 03/27/2026
The vulnerability CVE-2026-33063 affects the free5GC open source 5G core network implementation specifically within the Authentication Server Function (AUSF) component. This issue represents a critical improper null check flaw that can lead to complete service disruption. The vulnerability exists in the AUSF's UE authentication service endpoint at `/nausf-auth/v1/ue-authentications` and impacts all deployments of free5GC v4.0.1. The flaw stems from inadequate input validation and error handling within the authentication processing pipeline, making it particularly dangerous for 5G network infrastructure where authentication services are fundamental to network security and operations.
The technical root cause of this vulnerability lies in the `GetSupiFromSuciSupiMap` function which performs an unsafe interface conversion without proper nil checking. When the `SuciSupiMap` data structure is nil, the code attempts to convert an interface{} to a `context.SuciSupiMap` type, causing a runtime panic. This specific error condition "interface conversion: interface {} is nil, not context.SuciSupiMap" demonstrates a classic null pointer dereference scenario that has been classified under CWE-476 as "NULL Pointer Dereference". The vulnerability occurs during the authentication process when a remote attacker crafts a malicious UE authentication request that triggers this specific code path, leading to an unhandled panic that crashes the entire AUSF service.
The operational impact of this vulnerability is severe as it results in complete denial of service for the AUSF authentication service, effectively preventing legitimate user equipment from authenticating to the 5G network. This disruption cascades through the entire network infrastructure since the AUSF is responsible for critical authentication functions that enable secure access to network services. The vulnerability's remote exploitability means that attackers can trigger the service crash without requiring local access or elevated privileges, making it particularly dangerous in production environments. Network operators relying on free5GC for their 5G core network operations would face complete authentication service outages, potentially affecting thousands of connected devices and disrupting critical network functions according to ATT&CK framework category T1499 for Network Denial of Service.
The mitigation strategy for this vulnerability involves upgrading to free5GC version 1.4.2 which includes the necessary patch to address the improper null check. Since there are no application-level workarounds available, network administrators must implement immediate upgrades to prevent exploitation. Alternative approaches include restricting access to the AUSF API endpoints to trusted sources only, though this represents a temporary workaround rather than a permanent solution. The patch addresses the core issue by implementing proper nil checking before interface conversion operations, preventing the runtime panic that previously occurred when encountering nil values in the authentication processing pipeline. Organizations should also consider implementing network segmentation and access controls to limit exposure while applying the official patch to maintain service availability and network security posture.