CVE-2023-6764 in ATP
Summary
by MITRE • 02/20/2024
A format string vulnerability in a function of the IPSec VPN feature in Zyxel ATP series firmware versions from 4.32 through 5.37 Patch 1, USG FLEX series firmware versions from 4.50 through 5.37 Patch 1, USG FLEX 50(W) series firmware versions from 4.16 through 5.37 Patch 1, and USG20(W)-VPN series firmware versions from 4.16 through 5.37 Patch 1 could allow an attacker to achieve unauthorized remote code execution by sending a sequence of specially crafted payloads containing an invalid pointer; however, such an attack would require detailed knowledge of an affected device’s memory layout and configuration.
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Analysis
by VulDB Data Team • 01/21/2025
This vulnerability represents a critical format string flaw within the IPSec VPN implementation of several Zyxel network security devices including the ATP series, USG FLEX series, and USG20(W)-VPN series. The flaw exists in a specific function that processes incoming VPN traffic, where improper handling of user-supplied input data creates opportunities for attackers to manipulate the application's behavior through crafted payload sequences. The vulnerability specifically manifests when the system encounters invalid pointer references during the processing of IPSec VPN packets, which can trigger a format string exploitation vector that ultimately leads to remote code execution capabilities.
The technical nature of this vulnerability aligns with CWE-134, which describes format string vulnerabilities where format specifiers in user-controllable input are processed without proper validation. In this case, the exploitation requires attackers to send specially crafted packets that contain invalid pointers, which when processed by the vulnerable function can cause the application to read from or write to arbitrary memory locations. The attack scenario necessitates detailed knowledge of the target device's memory layout and configuration, as attackers must understand how the system organizes memory to successfully execute malicious code. This requirement for memory layout knowledge makes the attack more sophisticated but does not eliminate the severity of the vulnerability.
From an operational impact perspective, this vulnerability exposes organizations to significant risk as it allows unauthorized remote code execution without requiring authentication credentials. The attack vector operates over the network interface where IPSec VPN services are accessible, meaning that an attacker positioned within network reach could potentially compromise the device and gain full administrative control. This capability enables attackers to establish persistent access, exfiltrate sensitive data, modify network configurations, or use the compromised device as a pivot point for further attacks within the network infrastructure. The vulnerability affects multiple device series across different firmware versions, creating a broad attack surface that organizations must address through immediate remediation efforts.
The mitigation strategy for this vulnerability requires immediate firmware updates from Zyxel to address the format string handling issues in the IPSec VPN implementation. Organizations should prioritize updating all affected devices to the latest firmware versions that contain patches for this specific vulnerability. Network segmentation and access controls should be implemented to limit exposure of vulnerable devices to untrusted networks. Security monitoring should be enhanced to detect unusual VPN traffic patterns that might indicate exploitation attempts. Additionally, implementing network intrusion detection systems with signatures for known exploitation patterns and conducting regular vulnerability assessments can help identify and remediate similar issues before they can be exploited. The ATT&CK framework categorizes this vulnerability under T1059.007 for remote code execution and T1566 for initial access through network services, highlighting the multi-layered attack surface this vulnerability creates for network defenders.