CVE-2026-71676 in Open5GS
Summary
by MITRE • 08/18/2026
Buffer Overflow vulnerability in Open5GS v.2.7.0 allows a remote attacker to cause a denial of service via the NAS 5GS decoder chain, triggered when the message type byte of a NAS PDU is mutated
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Analysis
by VulDB Data Team • 08/18/2026
The identified security flaw resides within the Network Access Stratum five generation system decoding logic of Open5GS version two point seven zero. This vulnerability manifests as a buffer overflow condition that can be exploited by an unauthenticated remote attacker to disrupt service availability. The core technical issue stems from insufficient validation and bounds checking when processing incoming Non-Access Strategy Protocol Data Units. Specifically, the decoder chain fails to adequately verify the integrity of the message type byte before proceeding with subsequent parsing operations. When this specific field is mutated or contains unexpected values, the internal state machine may misinterpret the length or structure of the remaining payload data. This miscalculation leads to an attempt to write beyond the allocated memory boundaries for the buffer handling these NAS messages.
From a technical perspective, the vulnerability exploits the lack of rigorous input sanitization in the protocol parsing engine. The NAS layer is responsible for signaling between the user equipment and the core network functions, making it a critical component for session management and mobility procedures. By manipulating the message type byte, an attacker can trigger logic paths that assume valid data structures where none exist. This discrepancy causes the application to read or write memory locations outside its designated heap or stack segments. The resulting buffer overflow corrupts adjacent memory regions, which typically leads to immediate process termination due to segmentation faults or general protection violations. In some execution environments, this corruption could potentially be leveraged for arbitrary code execution if specific control flow hijacking techniques are applied, although the primary reported impact is denial of service through application crash.
The operational impact of this vulnerability is significant for network operators relying on Open5GS for private fifth generation deployments or testing environments. A successful exploitation results in a complete denial of service as the affected process crashes and must be restarted to restore functionality. This disruption affects all connected user equipment, halting data sessions and signaling procedures until the service is restored. Furthermore, repeated attempts to exploit this flaw can cause resource exhaustion if not properly monitored, potentially impacting system stability beyond just the single crashed instance. The vulnerability highlights a critical gap in the robustness of protocol implementations against malformed or maliciously crafted inputs, which are common vectors for automated attacks targeting telecommunications infrastructure.
Mitigation strategies should focus on immediate patching and defensive coding practices. Administrators must upgrade to a version of Open5GS that includes fixes for this buffer overflow condition, ensuring that all security patches released by the vendor are applied promptly. In scenarios where upgrading is not immediately feasible, network-level controls such as firewalls or intrusion prevention systems can be configured to inspect NAS traffic and drop packets with anomalous message type bytes or malformed protocol structures before they reach the vulnerable application layer. Additionally, implementing strict input validation within the software development lifecycle is essential for preventing similar issues in future releases. Developers should enforce bounds checking on all buffer operations derived from external inputs and utilize static analysis tools to detect potential memory safety violations early in the code review process.
This vulnerability aligns with Common Weakness Enumeration identifier CWE-120, which describes a buffer copy without checking size limits, leading to overflow conditions. It also relates to CWE-20, indicating improper input validation where external data is not sufficiently verified before processing. From an offensive security perspective, the exploitation technique falls under MITRE ATT&CK tactic Tactic TA0004, specifically referencing techniques associated with privilege escalation or defense evasion through memory corruption if code execution were possible. However, in its current manifestation as a denial of service vector, it primarily impacts availability metrics within the CIA triad. Continuous monitoring for unusual spikes in NAS signaling errors and process restarts can serve as an effective detection mechanism for ongoing exploitation attempts against this specific flaw.