CVE-2017-16659 in assp
Summary
by MITRE
The Gentoo mail-filter/assp package 1.9.8.13030 and earlier allows local users to gain privileges by leveraging access to the assp user account to install a Trojan horse /usr/share/assp/assp.pl script.
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Analysis
by VulDB Data Team • 12/05/2019
The vulnerability identified as CVE-2017-16659 resides within the Gentoo mail-filter/assp package version 1.9.8.13030 and earlier, representing a critical local privilege escalation flaw that exploits the trust relationship between system components and user accounts. This issue specifically targets the assp user account, which serves as the designated system user for running the Anti-Spam SMTP Proxy service. The vulnerability stems from inadequate privilege separation and improper file system permissions that allow a local attacker with access to the assp user account to manipulate critical system files, particularly the primary executable script located at /usr/share/assp/assp.pl. The flaw demonstrates a clear violation of the principle of least privilege, where the assp user account should only have access to its designated operational directories and files, yet can leverage its access to install malicious payloads that can escalate privileges beyond its intended scope.
This vulnerability operates through a classic Trojan horse attack vector where the malicious actor places a modified version of the assp.pl script in the system directory, effectively replacing the legitimate executable with a compromised version that can execute arbitrary code with elevated privileges. The technical implementation of this exploit relies on the assumption that the assp user account has write permissions to the /usr/share/assp/ directory, which typically should not be writable by non-root users. When the system executes the modified script, it inadvertently runs malicious code that can perform privilege escalation attacks, potentially allowing the attacker to gain root access or elevate their privileges to other system accounts with broader permissions. This represents a fundamental failure in the principle of least privilege and proper access control mechanisms that should prevent local users from modifying critical system components.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it provides attackers with a persistent foothold within the system that can be leveraged for further malicious activities. Once an attacker gains access to the assp user account and successfully installs the Trojan horse script, they can maintain long-term access while potentially remaining undetected by standard monitoring systems. The vulnerability affects systems that rely on the ASSP service for email filtering and spam protection, making it particularly dangerous in enterprise environments where email security is critical. This flaw can be exploited by attackers who have already gained access to a low-privilege account through other means, such as credential theft or exploitation of web application vulnerabilities, and then use this privilege escalation vulnerability to move laterally within the network. The attack chain typically involves initial compromise through other vectors followed by privilege escalation using this specific flaw, which aligns with the MITRE ATT&CK framework's privilege escalation tactics and techniques.
From a security controls perspective, this vulnerability highlights the critical importance of proper file system permissions and privilege separation in system design. The flaw violates several security best practices including proper access control implementation, secure file system permissions, and the principle of least privilege enforcement. Organizations should implement robust file integrity monitoring solutions that can detect unauthorized modifications to critical system scripts and executable files. The vulnerability also demonstrates the need for regular security audits and proper system hardening procedures that ensure system accounts have minimal required permissions. Security professionals should consider implementing mandatory access controls and file system integrity checking mechanisms such as tripwire or AIDE to detect unauthorized modifications to system files. Additionally, regular security updates and patch management processes are crucial for preventing exploitation of such vulnerabilities, as the issue affects versions of the software that were released prior to proper security hardening measures being implemented. The vulnerability serves as a reminder of the importance of maintaining current security practices and ensuring that system services operate with the minimal required privileges to prevent escalation attacks.