CVE-2026-67394 in Plesk
Summary
by MITRE • 09/01/2026
A critical local privilege escalation via OS command injection vulnerability has been discovered in Plesk for Linux, affecting all versions from 18.0.34 before 18.0.79.9 and 18.0.80.5. The vulnerability allows a customer or reseller with shell access (or allowed to change their own shell access) to elevate privileges to the root account on the hosting server.
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Analysis
by VulDB Data Team • 09/01/2026
A critical local privilege escalation vulnerability has been identified within Plesk for Linux, specifically impacting versions ranging from 18.0.34 up to but not including 18.0.79.9 and version 18.0.80.5. This flaw represents a severe security risk as it enables an attacker with limited shell access privileges to escalate their permissions to the root level on the hosting server. The vulnerability is classified under OS command injection, which falls broadly within CWE-78 Improper Neutralization of Special Elements used in an OS Command according to common weakness enumeration standards. This type of flaw occurs when a software application constructs system commands using externally influenced input without sufficiently neutralizing dangerous elements that could alter the intended command logic. In this specific instance, the vulnerability allows users who possess shell access or have the ability to modify their own shell settings to inject malicious payloads into administrative processes running with higher privileges.
The operational impact of this vulnerability is profound for hosting providers and managed service operators using affected Plesk versions. Since the attack vector requires local shell access, it typically targets compromised customer accounts or reseller panels that have been granted limited command-line capabilities. Once an attacker gains a foothold through these lower-privileged accounts, they can exploit the flaw to execute arbitrary commands as root. This effectively bypasses all isolation mechanisms designed to separate individual hosting customers from one another and from the underlying operating system infrastructure. An adversary achieving root access can read sensitive configuration files, steal database credentials, install persistent backdoors, or pivot laterally across other virtual machines hosted on the same physical server. The ability to escalate privileges so easily undermines the fundamental security model of multi-tenant hosting environments where isolation is paramount for data confidentiality and integrity.
From a tactical perspective, this vulnerability aligns with ATT&CK technique T1059 Command and Scripting Interpreter, specifically regarding local command execution via injection vectors. It also relates to privilege escalation techniques such as those found in the Local Privilege Escalation category where attackers leverage misconfigurations or software bugs to gain higher-level access. The presence of this flaw suggests that input validation mechanisms within specific Plesk components responsible for handling shell configuration changes are insufficiently robust. Attackers can likely manipulate parameters related to user shell assignments or command execution contexts to inject additional operating system commands that the privileged daemon will execute without proper sanitization. This creates a direct path from low-privilege web application access to full control over the host machine, which is considered one of the most dangerous scenarios in cloud and hosting security architectures.
Mitigation strategies must prioritize immediate patching for all systems running vulnerable versions of Plesk on Linux platforms. Administrators should upgrade to version 18.0.79.9 or later, or specifically version 18.0.80.5 and newer, where the underlying code has been corrected to properly sanitize inputs before constructing OS commands. In environments where immediate patching is not feasible due to compatibility concerns, temporary mitigations should include restricting shell access for customer accounts wherever possible. Implementing strict firewall rules to limit outbound connections from compromised containers or virtual machines can also reduce the blast radius of a successful exploitation attempt. Additionally, deploying host-based intrusion detection systems that monitor for unusual privilege escalation events or unexpected root-level command executions can help in early detection and response. Regular audits of user permissions and shell assignments within Plesk are essential to ensure that only necessary accounts retain elevated access capabilities, thereby reducing the attack surface available to potential adversaries seeking local privilege escalation opportunities.