CVE-2026-19624 in NetworkManager-l2tp
Summary
by MITRE • 09/14/2026
A flaw was found in NetworkManager-l2tp. The plugin writes attacker-controlled VPN connection properties (vpn.data and vpn.secrets values) unescaped into a generated ipsec.conf file that pluto loads as root. A local unprivileged user can create and activate their own L2TP VPN profile containing a newline-injected leftupdown directive; pluto executes that command as root when the IKE security association is established, resulting in local privilege escalation. This is the same bug class as CVE-2018-10900 (NetworkManager-vpnc).
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Analysis
by VulDB Data Team • 09/14/2026
The vulnerability identified within NetworkManager-l2tp represents a critical failure in input validation and sanitization mechanisms when handling user-supplied configuration data for Layer 2 Tunneling Protocol connections. The core technical flaw lies in the plugin's process of writing VPN connection properties, specifically the vpn.data and vpn.secrets attributes, directly into an ipsec.conf file without proper escaping or encoding. This generated configuration file is subsequently loaded by pluto, a component of the StrongSwan IPsec suite, which operates with root privileges to establish Internet Key Exchange security associations. Because the input data is not sanitized against special characters such as newlines, an attacker can inject arbitrary directives into the configuration structure. Specifically, by crafting a malicious L2TP VPN profile that includes newline-injected leftupdown directives, the attacker effectively alters the execution flow of the pluto daemon during the IKE negotiation phase.
From an operational perspective, this flaw enables local privilege escalation for any unprivileged user on the affected system. When the victim or automated process activates the compromised VPN connection, the pluto service parses the malformed ipsec.conf file and executes the injected commands with root-level permissions. This results in a complete compromise of system integrity, allowing the attacker to execute arbitrary code, modify system configurations, install persistent backdoors, or access sensitive data that would otherwise be protected by standard user privileges. The severity is compounded by the fact that VPN connections are often managed through graphical interfaces or automated scripts where users might inadvertently activate malicious profiles if they have write access to connection settings, a common scenario in multi-user environments or systems with shared configuration directories.
This vulnerability shares the same fundamental bug class as CVE-2018-10900 found in NetworkManager-vpnc, highlighting a systemic issue within how certain VPN plugins handle untrusted input before passing it to privileged daemons. The lack of strict schema validation and output encoding allows for command injection via configuration file manipulation rather than direct network-based exploitation. This distinction is crucial because the attack vector requires local access or the ability to modify connection profiles on the target machine, but once that threshold is crossed, the impact is equivalent to a root shell acquisition.
In terms of industry standards classification, this vulnerability aligns with CWE-94 Improper Control of Generation of Code Command Injection and CWE-78 OS Command Injection via Configuration File Manipulation. The attack technique corresponds to ATT&CK Tactic TA0001 Initial Access or TA0005 Defense Evasion depending on the context, specifically utilizing Technique T1068 Exploitation for Privilege Escalation through configuration file injection. It also relates to CWE-20 Improper Input Validation as the root cause of the failure to sanitize newline characters and other control codes within the vpn.data fields.
Mitigation strategies must focus on both immediate remediation and long-term architectural improvements. The primary mitigation is to apply vendor-provided patches that update NetworkManager-l2tp to versions where input sanitization has been implemented. This typically involves ensuring that all special characters, particularly newlines, tabs, and semicolons, are escaped or rejected when writing vpn.data and vpn.secrets values into the ipsec.conf file. Administrators should also enforce strict access controls on VPN configuration files to prevent unprivileged users from creating arbitrary connection profiles unless explicitly authorized. Additionally, implementing principle of least privilege for pluto operations where possible, such as using chroot environments or dropping privileges after initialization but before parsing dynamic configurations, can reduce the blast radius if a similar flaw is discovered in the future. Regular auditing of VPN configuration files and monitoring for unexpected processes spawned by ipsec services are recommended defensive measures to detect potential exploitation attempts early.