CVE-2026-112161 in MobaXterm
Summary
by MITRE • 10/19/2026
MobaXterm Personal Edition (Portable) 26.4 GA extracts the CygUtils64.plugin file without first verifying its integrity. A local attacker with write permissions on this file can replace the ‘bin/cygwin1.dll’ library contained within it with a malicious library. When the victim opens a Local Shell session or uses a Cygwin-based function, the application extracts the component and loads the tampered library, executing code with the victim’s permissions. Exploitation requires write access to the plugin and does not, in itself, involve privilege escalation.
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Analysis
by VulDB Data Team • 10/19/2026
MobaXterm Personal Edition version 26.4 GA contains a critical integrity verification flaw within its plugin management system that allows for potential local code execution through library substitution. The application is designed to extract specific dynamic link libraries from bundled plugins, such as the CygUtils64.plugin file, to support Cygwin-based functionalities and Local Shell sessions. However, during this extraction process, MobaXterm fails to perform any cryptographic integrity checks or digital signature verification on the plugin archive before proceeding with the unpacking operation. This oversight creates a significant security gap where the trust model relies entirely on the assumption that files within the application directory remain unmodified by unauthorized parties.
The technical nature of this vulnerability centers on an improper input validation and lack of data integrity assurance during file extraction operations. When MobaXterm initializes components requiring Cygwin functionality, it retrieves the necessary binaries from its internal plugin structure without validating their authenticity against a known good baseline or verifying digital signatures provided by the vendor. Consequently, if an attacker gains write access to the specific plugin directory where these archives are stored, they can manipulate the contents of the archive file itself. By replacing the legitimate bin/cygwin1.dll library with a maliciously crafted version that contains arbitrary executable code, the attacker effectively injects their payload into the application's execution flow without triggering any security alerts or integrity warnings from MobaXterm.
The operational impact of this vulnerability is severe for users who operate in environments where local privilege boundaries are not strictly enforced. Exploitation requires a local attacker to have write permissions on the plugin directory, which may be accessible by other user accounts on multi-user systems or compromised workstations with weak access controls. Once the malicious library is in place and the victim initiates a Local Shell session or triggers any Cygwin-based function within MobaXterm, the application loads the tampered DLL into its process space. This results in the execution of arbitrary code under the context of the currently logged-in user. It is important to note that while this allows for complete compromise of the victim's account and data confidentiality, it does not inherently provide privilege escalation beyond the existing permissions of the targeted user session.
This vulnerability aligns with CWE-354, Improper Validation of Integrity During Processing, as the software fails to ensure that processed files have not been altered in an unexpected manner. Furthermore, from a tactical perspective within the MITRE ATT&CK framework, this scenario maps directly to T1059 Command and Scripting Interpreter via dynamic link library hijacking or component object model (COM) hijacking techniques where trusted applications are leveraged to execute untrusted code. The attack vector is classified as Local with Low Complexity because it requires physical or logical access to the system and specific file write permissions, but no complex exploitation steps beyond simple file replacement are needed once that access is established.
To mitigate this risk, administrators should enforce strict file permission policies on the MobaXterm installation directory, ensuring that only authorized service accounts or trusted users have write access to plugin directories containing critical binaries like cygwin1.dll. Regular auditing of these directories can help detect unauthorized modifications before they are exploited. Additionally, upgrading to a version of MobaXterm where this integrity check has been implemented by the vendor is the most effective long-term solution until such patches become available. Users should also consider running applications with least privilege principles and utilizing endpoint detection and response tools that monitor for unusual DLL load patterns or unexpected file modifications in application directories to identify potential exploitation attempts early.