CVE-2026-105429 in NetBird
Summary
by MITRE • 10/14/2026
Improper neutralization of special elements in the NetBird client SSH configuration manager (client/ssh/config/manager.go) in NetBird versions 0.60.0 through 0.74.6 allows a malicious or compromised peer to execute arbitrary commands on other NetBird client hosts. The client writes a system-wide OpenSSH drop-in file (/etc/ssh/ssh_config.d/99-netbird.conf, or the equivalent under %PROGRAMDATA%\ssh\ssh_config.d on Windows) that embeds each peer FQDN or hostname inside a double-quoted Match host directive without escaping. A peer name containing a double quote breaks out of the quoted context and injects arbitrary SSH configuration directives, including exec commands, which run locally as any user on the host the next time that user runs ssh. Desktop clients on Linux, macOS, Windows and FreeBSD are affected; the Android and iOS apps are not. The issue is fixed in version 0.74.7, which accepts a peer FQDN or hostname only if it is a valid DNS name.
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Analysis
by VulDB Data Team • 10/14/2026
The vulnerability identified as improper neutralization of special elements within the NetBird client SSH configuration manager represents a critical input validation failure that enables remote code execution through maliciously crafted hostnames. This flaw resides in the component responsible for managing SSH configurations, specifically affecting versions 0.60.0 through 0.74.6 across Linux, macOS, Windows, and FreeBSD desktop clients. The core technical issue stems from how the application constructs system-wide OpenSSH drop-in configuration files located at /etc/ssh/ssh_config.d/99-netbird.conf on Unix-like systems or %PROGRAMDATA%\ssh\ssh_config.d on Windows environments. When a peer joins the NetBird mesh network, its Fully Qualified Domain Name (FQDN) or hostname is embedded directly into a double-quoted Match host directive within this configuration file without any sanitization or escaping of special characters.
The operational impact of this vulnerability is severe because it allows an attacker who controls or compromises one peer in the NetBird network to execute arbitrary commands on other client hosts. By injecting a peer name that contains a double quote character, the malicious actor can break out of the quoted context defined by the SSH configuration syntax. This breakout enables the injection of additional SSH configuration directives, most critically the exec command directive. When any user on the affected host subsequently initiates an SSH connection to a target matching the injected pattern, the OpenSSH client parses the corrupted configuration file and executes the attacker-specified commands with the privileges of that user. This mechanism effectively turns the trusted peer discovery process into a vector for lateral movement and privilege escalation within the network infrastructure.
From a classification perspective, this vulnerability aligns closely with CWE-78 Improper Neutralization of Special Elements used in an OS Command (OS Command Injection) and CWE-20 Improper Input Validation. The failure to validate that peer identifiers conform to strict DNS naming conventions allows non-compliant characters to alter the execution context of a system utility. In terms of attack tactics, this behavior is consistent with ATT&CK technique T1587 Development of Capabilities, specifically sub-technique T1587.002 Malicious Code, as it involves creating artifacts that facilitate unauthorized command execution. It also relates to T1610 Deploy Payload via Network Share or similar lateral movement techniques depending on how the exec directive is leveraged post-exploitation.
The scope of this vulnerability excludes mobile applications running on Android and iOS, limiting the attack surface primarily to desktop operating systems where system-wide SSH configuration files are actively used by users for remote access operations. The risk is particularly acute in environments where NetBird clients are deployed with elevated privileges or where users frequently initiate SSH sessions to various hosts within the mesh network. An attacker does not need direct shell access to the target machine; merely controlling a peer node and ensuring its hostname contains specific malicious payloads is sufficient to trigger the vulnerability when other peers connect via SSH.
Mitigation strategies must prioritize immediate software updates as the primary defense vector. The issue has been resolved in NetBird version 0.74.7, which implements strict validation logic that accepts peer FQDNs or hostnames only if they conform to valid DNS name standards. This fix effectively neutralizes the injection attack by preventing special characters like double quotes from entering the configuration generation process. Organizations running affected versions should upgrade immediately and audit their NetBird network for any peers with suspiciously named hosts that may have been used in previous exploitation attempts. Additionally, administrators should consider implementing additional input validation layers at the application level to ensure robustness against future variations of this class of vulnerability.