CVE-2007-6358 in pdftops
Summary
by MITRE
pdftops.pl before 1.20 in alternate pdftops filter allows local users to overwrite arbitrary files via a symlink attack on the pdfin.[PID].tmp temporary file, which is created when pdftops reads a PDF file from stdin, such as when pdftops is invoked by CUPS.
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Analysis
by VulDB Data Team • 08/01/2019
The vulnerability described in CVE-2007-6358 represents a critical security flaw in the pdftops.pl script version 1.20 and earlier, which is part of the poppler-utils package commonly used for PDF processing in Unix-like systems. This vulnerability specifically affects the alternate pdftops filter implementation that is invoked by the Common Unix Printing System CUPS when processing PDF documents for printing. The flaw stems from improper handling of temporary files during the PDF conversion process, creating a predictable race condition that can be exploited by local attackers to overwrite arbitrary files on the system.
The technical mechanism behind this vulnerability involves the creation of a temporary file named pdfin.PID.tmp where PID represents the process identifier of the pdftops.pl script. When pdftops is invoked by CUPS to process a PDF file from stdin, the script generates this temporary file in a predictable location within the system's temporary directory. The vulnerability arises because the script creates this temporary file without proper security checks, and more critically, does not verify that the temporary file is created with appropriate permissions and ownership. This behavior creates a window of opportunity for malicious users to establish symbolic links to target files before the legitimate script creates the temporary file, thereby allowing them to control what gets written to the target location.
From an operational perspective, this vulnerability poses significant risks to systems that rely on CUPS for printing services and PDF processing. Attackers with local access to the system can exploit this weakness to overwrite critical system files, configuration files, or even executable programs, potentially leading to privilege escalation or persistent backdoors. The vulnerability is particularly concerning because it operates within the context of a system service that typically runs with elevated privileges, meaning that successful exploitation could result in unauthorized system compromise. The attack requires only local access and basic understanding of Unix file system operations, making it relatively easy to exploit compared to remote vulnerabilities.
The vulnerability maps to CWE-367, which describes Time-of-Check to Time-of-Use (TOCTOU) race conditions, and also relates to CWE-22, which covers improper limitation of a pathname to a restricted directory. In the context of the MITRE ATT&CK framework, this vulnerability aligns with techniques involving privilege escalation and persistence mechanisms, as attackers could use it to modify system binaries or configuration files to maintain access. The attack vector falls under the category of local privilege escalation, specifically targeting the print system service execution context. The impact is further amplified by the fact that CUPS is a widely deployed printing system across enterprise environments, making this vulnerability potentially widespread in affected organizations.
Mitigation strategies for this vulnerability should focus on immediate patching of the pdftops.pl script to version 1.20 or later, which includes proper temporary file handling mechanisms. Organizations should also implement proper file system permissions and access controls, ensuring that temporary directories are not writable by unprivileged users. Additionally, system administrators should consider implementing file system monitoring to detect unauthorized symbolic link creation in temporary directories. The recommended approach includes verifying that temporary files are created with proper permissions and ownership, using atomic file creation methods, and implementing proper input validation to prevent predictable temporary file names. Regular security auditing of system services and print queue configurations should also be conducted to identify and remediate similar vulnerabilities in other components of the printing infrastructure.