CVE-1999-1102 in lpr
Summary
by MITRE
lpr on SunOS 4.1.1, BSD 4.3, A/UX 2.0.1, and other BSD-based operating systems allows local users to create or overwrite arbitrary files via a symlink attack that is triggered after invoking lpr 1000 times.
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Analysis
by VulDB Data Team • 04/20/2026
The vulnerability identified as CVE-1999-1102 represents a critical file system security flaw affecting multiple BSD-based operating systems including SunOS 4.1.1, BSD 4.3, and A/UX 2.0.1. This issue specifically targets the lpr print spooling utility which is responsible for managing print jobs in Unix-like environments. The vulnerability stems from improper handling of temporary files during the print job processing cycle, creating a predictable pattern that can be exploited by local users to manipulate the file system. The flaw manifests when the lpr utility is invoked repeatedly, specifically after 1000 invocations, at which point the symlink attack mechanism becomes exploitable.
The technical implementation of this vulnerability involves the lpr utility's reliance on predictable temporary file names and its failure to properly validate symbolic link references during the print job processing. When lpr executes repeatedly, it creates temporary files in predictable locations with predictable naming conventions, allowing local attackers to establish symbolic links in advance of these temporary file creation events. This creates a race condition where the attacker can control the target of the symbolic link, enabling them to redirect file operations to arbitrary locations on the file system. The vulnerability operates under CWE-377, which classifies the weakness as "Insecure Temporary File Creation," and specifically relates to CWE-59, "Improper Link Resolution," highlighting the dangerous interaction between temporary file handling and symbolic link resolution.
The operational impact of this vulnerability is significant as it allows local users to gain unauthorized file system access and potentially escalate privileges within the system. Attackers can leverage this weakness to overwrite critical system files, create malicious files in sensitive directories, or manipulate print job processing to redirect output to unintended locations. The requirement for 1000 invocations before exploitation means the attack must be carefully timed and executed, but once triggered, it provides persistent access to the file system manipulation capabilities. This vulnerability directly maps to techniques described in the MITRE ATT&CK framework under T1059 for command and script injection, and T1078 for valid accounts, as it exploits legitimate system utilities to gain unauthorized access to file system resources. The attack vector specifically aligns with T1548.001 for abuse of sudo privileges and T1068 for local privilege escalation through system utility manipulation.
The mitigation strategies for CVE-1999-1102 require immediate system administrators to implement proper file system permissions and access controls for temporary directories used by lpr. The most effective immediate solution involves restricting write access to temporary directories and ensuring that the lpr utility properly validates symbolic links before creating temporary files. System administrators should also consider implementing file system monitoring to detect suspicious symlink creation patterns and apply patches or updates to the lpr utility that address the predictable temporary file naming issue. Additionally, the use of more secure print spooling utilities or implementing proper input validation and sanitization for temporary file operations can prevent similar vulnerabilities from occurring in future system deployments. The vulnerability demonstrates the critical importance of proper temporary file handling in system utilities and the potential for seemingly benign operations to create significant security risks when not properly secured against race conditions and symbolic link attacks.