CVE-2022-26531 in USG
Summary
by MITRE • 05/24/2022
Multiple improper input validation flaws were identified in some CLI commands of Zyxel USG/ZyWALL series firmware versions 4.09 through 4.71, USG FLEX series firmware versions 4.50 through 5.21, ATP series firmware versions 4.32 through 5.21, VPN series firmware versions 4.30 through 5.21, NSG series firmware versions 1.00 through 1.33 Patch 4, NXC2500 firmware version 6.10(AAIG.3) and earlier versions, NAP203 firmware version 6.25(ABFA.7) and earlier versions, NWA50AX firmware version 6.25(ABYW.5) and earlier versions, WAC500 firmware version 6.30(ABVS.2) and earlier versions, and WAX510D firmware version 6.30(ABTF.2) and earlier versions, that could allow a local authenticated attacker to cause a buffer overflow or a system crash via a crafted payload.
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Analysis
by VulDB Data Team • 05/10/2026
The vulnerability CVE-2022-26531 represents a critical input validation weakness affecting multiple Zyxel network security appliances including USG, ZyWALL, ATP, VPN, NSG, NXC2500, NAP203, NWA50AX, WAC500, and WAX510D series devices. This flaw exists within the command line interface implementation of affected firmware versions spanning from 4.09 through 5.21 for USG/ZyWALL series up to 6.30(AAIG.3) and earlier for NXC2500, with various intermediate versions across different product lines. The vulnerability manifests as improper input validation in CLI commands that process user-supplied data without adequate sanitization or bounds checking mechanisms.
The technical exploitation of this vulnerability occurs through buffer overflow conditions that can be triggered by sending crafted payloads to vulnerable CLI endpoints. When authenticated local attackers submit malicious input to these command interfaces, the system fails to properly validate the input length or content, allowing the attacker to exceed allocated buffer boundaries. This buffer overflow condition directly leads to system instability and potential crashes, effectively creating a denial of service condition that can disrupt network security operations. The vulnerability specifically affects the command line interface functionality, which represents a critical attack surface for privilege escalation and system compromise scenarios.
From an operational impact perspective, this vulnerability creates significant security risks for organizations relying on Zyxel security appliances. The local authenticated nature of the attack means that an attacker who has already gained access to legitimate user credentials can exploit this weakness to cause service disruption, potentially leading to extended downtime for critical network security functions. The impact extends beyond simple denial of service as the system crashes may result in loss of network monitoring capabilities, firewall rule enforcement, and other essential security functions that these appliances provide. Organizations with multiple affected devices across their network infrastructure face compounded risk due to the widespread nature of the vulnerability across various product lines.
The vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions, and represents a classic example of improper input validation that can lead to arbitrary code execution or system compromise. From an attack framework perspective, this vulnerability maps to ATT&CK techniques including privilege escalation through command execution and denial of service via system instability. The affected CLI commands likely process user input through standard C string handling functions without proper bounds checking, creating opportunities for attackers to manipulate memory layout and potentially execute malicious code. Organizations should immediately assess their inventory for affected firmware versions and implement remediation measures including firmware updates, network segmentation, and enhanced access controls for CLI interfaces. The vulnerability demonstrates the importance of input validation in security-critical system components and highlights the need for comprehensive security testing of command line interfaces in network security appliances.