CVE-2026-91840 in NetworkManager-vpnc
Summary
by MITRE • 09/25/2026
A flaw was found in NetworkManager-vpnc. This vulnerability allows a local unprivileged user to escalate privileges to root. By injecting a newline character into the VPN username field, an attacker can manipulate the vpnc configuration to execute an arbitrary program with root privileges when the malicious VPN connection is activated.
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Analysis
by VulDB Data Team • 09/25/2026
The vulnerability identified in NetworkManager-vpnc represents a critical local privilege escalation flaw that stems from improper input validation within the VPN client's configuration handling mechanisms. This issue specifically affects systems utilizing the vpnc backend for managing Virtual Private Network connections, allowing any unprivileged user with access to create or modify network connection profiles to gain unauthorized administrative control over the host system. The core of the problem lies in how the application processes special characters within credential fields before passing them to underlying configuration scripts and executables that operate with elevated privileges.
The technical root cause is a classic command injection vulnerability resulting from insufficient sanitization of user-supplied data, specifically newline characters injected into the VPN username field. When an attacker creates a malicious network connection profile containing a crafted username with embedded newlines, these characters break out of the expected string context during configuration generation. This structural manipulation allows the attacker to append arbitrary commands that are subsequently executed by root-level processes when the VPN connection is established or reconfigured. The vulnerability exploits the trust relationship between the user-space NetworkManager daemon and the privileged helper scripts responsible for applying network configurations, effectively bypassing standard access controls through injection techniques rather than exploiting a memory corruption flaw.
From an operational perspective, this vulnerability poses a severe risk to system integrity and confidentiality on multi-user systems or shared infrastructure where local users do not inherently possess root privileges. An attacker who successfully exploits this flaw can execute arbitrary code with full administrative rights, leading to complete compromise of the operating system. This includes the ability to install persistent backdoors, exfiltrate sensitive data from other user accounts, modify system configurations, and disable security controls such as firewalls or audit logging. The impact is particularly acute in environments where NetworkManager-vpnc is used for establishing site-to-site tunnels or remote access connections that require automatic authentication upon connection activation.
This flaw aligns with CWE-78 Improper Neutralization of Special Elements used in an OS Command, commonly known as OS Command Injection, and falls under the MITRE ATT&CK technique T1068 Exploitation for Privilege Escalation. The attack vector is classified as Local (T1059) because it requires physical or logical access to a user account on the target system, but the impact is Remote Code Execution with elevated privileges due to the nature of the configuration execution context. Mitigation strategies should prioritize updating NetworkManager-vpnc to patched versions that properly escape or sanitize special characters in all input fields before processing. In environments where immediate patching is not feasible, administrators can mitigate risk by restricting user permissions to create new network connections via policy controls such as polkit rules, disabling the vpnc plugin if it is not actively required for business operations, and implementing strict file integrity monitoring on configuration directories to detect unauthorized changes. Regular auditing of system logs for unusual process executions following VPN connection attempts can also aid in early detection of exploitation attempts.