CVE-2019-3698 in Linux Enterprise Server
Summary
by MITRE
UNIX Symbolic Link (Symlink) Following vulnerability in the cronjob shipped with nagios of SUSE Linux Enterprise Server 12, SUSE Linux Enterprise Server 11; openSUSE Factory allows local attackers to cause cause DoS or potentially escalate privileges by winning a race. This issue affects: SUSE Linux Enterprise Server 12 nagios version 3.5.1-5.27 and prior versions. SUSE Linux Enterprise Server 11 nagios version 3.0.6-1.25.36.3.1 and prior versions. openSUSE Factory nagios version 4.4.5-2.1 and prior versions.
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Analysis
by VulDB Data Team • 04/07/2024
The vulnerability identified as CVE-2019-3698 represents a critical race condition flaw in the cronjob implementation of nagios monitoring software across multiple SUSE and openSUSE distributions. This security weakness specifically exploits the handling of symbolic links within the cron execution environment, creating a window where local attackers can manipulate file system operations to achieve unintended consequences. The vulnerability stems from the improper management of file descriptors and symbolic link resolution during the execution of scheduled tasks, allowing malicious users to exploit timing dependencies in the system's file access mechanisms.
The technical implementation of this flaw involves a classic race condition scenario where an attacker can create or modify symbolic links in a manner that causes the cronjob process to follow unintended paths during execution. When the nagios cronjob processes files, it does not properly validate or secure the symbolic link resolution process, enabling attackers to substitute legitimate files with malicious alternatives. This vulnerability manifests through the exploitation of the timing gap between when a file is checked for existence and when it is actually accessed, allowing attackers to replace the target file with a symbolic link pointing to a privileged location or executable. The issue is particularly dangerous because it can be leveraged for both denial of service attacks by causing the cronjob to fail or crash, and more severely for privilege escalation by redirecting execution to attacker-controlled code.
The operational impact of CVE-2019-3698 extends beyond simple service disruption, as it creates potential pathways for persistent system compromise. Attackers who successfully exploit this vulnerability can gain elevated privileges to execute arbitrary code with the privileges of the nagios user or potentially root access if the cronjob runs with elevated permissions. This threat model aligns with ATT&CK technique T1059.001 for command and script interpreter execution, and T1068 for exploit for privilege escalation. The vulnerability affects systems where nagios is configured to run with elevated privileges for monitoring tasks, making it particularly dangerous in enterprise environments where monitoring services often require administrative access to perform comprehensive system checks. The race condition nature of the flaw means that exploitation is not guaranteed but becomes increasingly likely with repeated attempts and proper timing.
Mitigation strategies for this vulnerability must address both the immediate security gap and the underlying system configuration issues that enable exploitation. Organizations should apply the vendor-provided patches immediately to update to versions that properly handle symbolic link resolution within cronjob contexts. System administrators should implement proper file permissions and access controls to minimize the impact of potential exploitation attempts. The remediation process should include reviewing all cronjob configurations to ensure that symbolic link following is disabled or properly validated. Security controls should be implemented to monitor for suspicious file system operations around cron execution times, as outlined in CWE-367. Additionally, system hardening measures should be applied to reduce the attack surface, including restricting write permissions to directories containing cronjob scripts and implementing proper file integrity monitoring to detect unauthorized modifications to critical system files. The vulnerability serves as a reminder of the importance of proper race condition handling in security-sensitive applications and the critical need for robust file system access controls in monitoring and automation frameworks.