CVE-2026-30058 in Free5GC
Summary
by MITRE • 08/27/2026
Improper Input Validation in the HTTPModifySubscription handler of free5gc v4.0.1 allows attackers to cause a Denial of Service (DoS) via a crafted input.
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Analysis
by VulDB Data Team • 08/27/2026
The vulnerability identified within the free5GC open-source 5G core network implementation, specifically affecting version 4.0.1, centers on an improper input validation flaw located in the HTTPModifySubscription handler. This component is responsible for processing subscription modification requests sent by user equipment or other network functions to update notification preferences and event subscriptions. The root cause of this issue lies in the insufficient sanitization and boundary checking of data fields received via Hypertext Transfer Protocol (HTTP) messages before they are processed by the underlying application logic. When an attacker constructs a malicious HTTP request containing specially crafted input parameters, such as excessively long strings, malformed JSON structures, or unexpected character sequences, the handler fails to reject these inputs appropriately. Instead of returning a standard error code and terminating the operation gracefully, the system proceeds with processing the invalid data, leading to internal state corruption, infinite loops, memory exhaustion, or unhandled exceptions that crash the service process.
From an operational perspective, this vulnerability poses a significant risk to the availability of critical 5G core network functions. Since free5GC is often deployed in testbeds and increasingly in production-like environments for commercial exploration, a successful exploitation can lead to a Denial of Service condition where the affected network function becomes unresponsive or restarts repeatedly. This disruption impacts not only the specific user attempting the attack but also other users sharing the same network slice or core instance, as the failure of one subscription management component can cascade into broader service degradation. The ability to trigger this state remotely via HTTP makes it particularly dangerous for any system exposed to external networks without adequate perimeter security controls.
In terms of industry standard classification, this vulnerability aligns with CWE-20 Improper Input Validation and potentially CWE-400 Uncontrolled Resource Consumption if the flaw leads to resource exhaustion such as memory leaks or CPU spikes during processing. From a tactical standpoint within the MITRE ATT&CK framework for Enterprise, this behavior is consistent with techniques related to Service Exploitation (T1529) where an attacker targets specific services to disrupt availability. The lack of robust input filtering represents a fundamental security design flaw that violates the principle of least privilege and defensive coding practices expected in telecommunications software.
To mitigate this vulnerability, immediate remediation should focus on updating free5GC to patched versions released by the maintainers after v4.0.1 where these validation checks have been implemented. In environments where patching is not immediately feasible, network-level mitigations are essential. Deploying Web Application Firewalls (WAF) with rules specifically tuned to detect and block anomalous HTTP payloads targeting subscription endpoints can provide a layer of defense against exploitation attempts. Additionally, implementing strict rate limiting on the affected API endpoints helps mitigate the impact by preventing rapid-fire requests that could exacerbate resource exhaustion conditions. Input validation logic should be hardened to enforce strict schema definitions for all incoming JSON bodies, ensuring that data types and lengths conform exactly to expected specifications before any processing occurs. Regular security audits focusing on input handling in HTTP handlers are recommended to identify similar flaws across other components of the core network infrastructure.