CVE-2000-0728 in Xpdf
Summary
by MITRE
xpdf PDF viewer client earlier than 0.91 allows local users to overwrite arbitrary files via a symlink attack.
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Analysis
by VulDB Data Team • 06/02/2019
The vulnerability identified as CVE-2000-0728 affects the xpdf PDF viewer client version 0.91 and earlier, presenting a significant security risk through its improper handling of symbolic links during file operations. This flaw enables local attackers to exploit the application's file creation mechanisms by manipulating symbolic links, thereby gaining unauthorized access to write operations on arbitrary files within the system. The vulnerability stems from the application's failure to properly validate file paths when creating temporary files, allowing malicious users to redirect file operations through carefully crafted symbolic link structures. The security implications extend beyond simple file overwrites as this weakness can potentially lead to privilege escalation or arbitrary code execution depending on the target file's permissions and the application's operational context.
The technical implementation of this vulnerability operates through a classic symlink attack pattern where the attacker creates a symbolic link with a specific name that matches a temporary file the vulnerable application intends to create. When xpdf processes PDF files and generates temporary files during rendering or processing operations, it does not adequately verify whether the target file path is a symbolic link before proceeding with file creation. This behavior aligns with CWE-59 symbolic link following weakness, specifically manifesting as improper handling of symbolic links in file operations. The flaw represents a directory traversal and file system manipulation vulnerability that violates fundamental security principles of file access control and path validation.
From an operational perspective, this vulnerability poses substantial risk to systems where xpdf is installed and used by local users, particularly in multi-user environments or systems where users have the ability to create symbolic links. The attack vector requires local access and basic file system manipulation capabilities, making it relatively accessible to attackers who already have user-level privileges on the target system. The impact extends beyond immediate file overwrites as attackers could potentially target critical system files, configuration files, or files belonging to other users with elevated privileges. This vulnerability particularly affects Unix-like systems where symbolic link functionality is native and commonly used, though similar issues could theoretically exist in other operating systems with comparable file system characteristics. The attack scenario typically involves an attacker creating a malicious symbolic link in a directory where the PDF viewer will create temporary files, then triggering the vulnerable application to process a PDF file that causes the application to follow the symbolic link and overwrite the target file.
Mitigation strategies for CVE-2000-0728 primarily focus on immediate software updates to xpdf version 0.91 or later, which contain proper symbolic link validation mechanisms. System administrators should also implement restrictive file permissions and ensure that users do not have the ability to create symbolic links in directories where xpdf or similar applications operate. The principle of least privilege should be enforced by running PDF viewers with minimal necessary permissions and avoiding execution as root or with elevated privileges. Additional protective measures include monitoring for suspicious symbolic link creation patterns and implementing file integrity monitoring systems to detect unauthorized file modifications. Organizations should also consider implementing network-based security controls and access restrictions to limit local user capabilities on systems where PDF viewing applications are installed. This vulnerability demonstrates the critical importance of proper input validation and file system operation security, aligning with ATT&CK technique T1059 command and script interpreter for execution and T1566 credential access through manipulation of file system objects. The remediation process should include thorough vulnerability assessment of all systems running xpdf or similar applications to identify potential exposure to similar weaknesses in the broader application ecosystem.