CVE-2016-0727 in Linux
Summary
by MITRE
The crontab script in the ntp package before 1:4.2.6.p3+dfsg-1ubuntu3.11 on Ubuntu 12.04 LTS, before 1:4.2.6.p5+dfsg-3ubuntu2.14.04.10 on Ubuntu 14.04 LTS, on Ubuntu Wily, and before 1:4.2.8p4+dfsg-3ubuntu5.3 on Ubuntu 16.04 LTS allows local users with access to the ntp account to write to arbitrary files and consequently gain privileges via vectors involving statistics directory cleanup.
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Analysis
by VulDB Data Team • 11/29/2024
The vulnerability described in CVE-2016-0727 represents a critical privilege escalation flaw within the Network Time Protocol (NTP) implementation on Ubuntu systems. This issue specifically affects the crontab script functionality within the ntp package, where local users with access to the ntp account can manipulate file permissions and execute arbitrary file operations. The vulnerability stems from improper handling of statistics directory cleanup processes that occur during regular NTP maintenance operations. Attackers exploiting this weakness can leverage the ntp user's privileges to write to files outside of the intended scope, potentially allowing them to modify system-critical files and escalate their privileges to root level access. The flaw exists in multiple Ubuntu LTS versions including 12.04, 14.04, and 16.04, demonstrating the widespread nature of this vulnerability across different system generations.
The technical implementation of this vulnerability involves the crontab script's interaction with the statistics directory cleanup mechanism, which operates under the ntp user context. When the cleanup process executes, it fails to properly validate file paths or implement adequate access controls, creating opportunities for path traversal and unauthorized file manipulation. This weakness aligns with CWE-22 Path Traversal and CWE-73 Path Traversal, where insufficient input validation allows attackers to manipulate file system access. The vulnerability specifically targets the NTP package's automated cleanup routines that manage statistics data files, which are typically stored in directories with specific permissions. However, due to flawed path resolution logic, an attacker can manipulate these cleanup operations to target arbitrary files on the system, potentially writing malicious content to critical system locations such as /etc/passwd or other privilege escalation targets.
The operational impact of CVE-2016-0727 extends beyond simple privilege escalation to encompass broader system compromise capabilities. An attacker who gains access to the ntp account can leverage this vulnerability to establish persistent access, modify system configuration files, or install backdoors that maintain administrative control over the compromised system. The vulnerability's exploitation requires only local access to the ntp account, making it particularly dangerous in environments where the ntp service runs with elevated privileges or where users might have legitimate access to this account for system administration purposes. This vulnerability directly maps to ATT&CK technique T1068 Privilege Escalation through the use of local service accounts and the exploitation of insufficient access controls within system maintenance scripts. The attack vector is particularly concerning because it operates through legitimate system maintenance processes, making detection more challenging and potentially allowing attackers to remain undetected for extended periods.
Mitigation strategies for CVE-2016-0727 primarily focus on applying the vendor-provided security patches that address the specific file path handling issues within the NTP package's crontab script. System administrators should immediately upgrade to the patched versions of the ntp package available for their Ubuntu LTS releases, specifically versions 1:4.2.6.p3+dfsg-1ubuntu3.11 for Ubuntu 12.04, 1:4.2.6.p5+dfsg-3ubuntu2.14.04.10 for Ubuntu 14.04, and 1:4.2.8p4+dfsg-3ubuntu5.3 for Ubuntu 16.04. Additionally, implementing proper access controls for the ntp account and monitoring the statistics directory cleanup processes can help detect potential exploitation attempts. System hardening measures should include restricting write access to the ntp user's home directory and related system directories, as well as implementing file integrity monitoring solutions to detect unauthorized modifications to critical system files. Network segmentation and privilege separation practices can further reduce the attack surface by limiting the potential impact of a compromised ntp account. Regular vulnerability assessments and security audits should be conducted to identify similar issues in other system maintenance scripts and ensure that all automated processes implement proper input validation and access control mechanisms.