CVE-2015-8327 in cups-filters
Summary
by MITRE
Incomplete blacklist vulnerability in util.c in foomatic-rip in cups-filters 1.0.42 before 1.2.0 and in foomatic-filters in Foomatic 4.0.x allows remote attackers to execute arbitrary commands via ` (backtick) characters in a print job.
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Analysis
by VulDB Data Team • 07/01/2022
The vulnerability CVE-2015-8327 represents a critical command injection flaw in the foomatic-rip component of cups-filters version 1.0.42 and earlier, as well as in foomatic-filters version 4.0.x. This issue stems from an incomplete blacklist implementation in the util.c file that fails to properly sanitize input containing backtick characters. The flaw exists within the print job processing pipeline where the system does not adequately validate or escape special characters that could be interpreted as shell command invocations by the underlying operating system.
The technical implementation of this vulnerability exploits the lack of comprehensive input validation in the print processing framework. When a print job contains backtick characters, these are interpreted by the shell as command substitution operators, allowing attackers to inject arbitrary shell commands that execute with the privileges of the printing service. This represents a classic command injection vulnerability that maps to CWE-78, which specifically addresses "Improper Neutralization of Special Elements used in a Command ('Command Injection')". The vulnerability occurs because the system relies on a blacklist approach rather than a whitelist validation mechanism, making it susceptible to bypasses through various encoding or obfuscation techniques.
Operationally, this vulnerability presents a significant risk to organizations relying on CUPS-based printing systems, as remote attackers can execute arbitrary commands on affected systems without authentication. The impact extends beyond simple command execution to potentially allow full system compromise, privilege escalation, and lateral movement within network environments. Attackers could leverage this vulnerability to install backdoors, exfiltrate sensitive data, or disrupt printing services. The vulnerability is particularly dangerous in enterprise environments where print servers often have elevated privileges and may be accessible from untrusted networks, creating a vector for both internal and external attacks.
Mitigation strategies for CVE-2015-8327 should focus on immediate patching of affected systems to upgrade to cups-filters version 1.2.0 or later, where the input validation has been properly implemented. Organizations should also implement network segmentation to limit access to print servers, deploy intrusion detection systems to monitor for suspicious print job patterns, and consider implementing additional input sanitization at the network level. The remediation aligns with ATT&CK technique T1059.001 for Command and Scripting Interpreter and T1078.004 for Valid Accounts, as attackers could leverage this vulnerability to establish persistent access through command execution and account manipulation. System administrators should also review and harden print server configurations, disable unnecessary print services, and implement proper access controls to minimize the attack surface. Regular security assessments and vulnerability scanning should be conducted to identify similar input validation weaknesses in other system components.