CVE-2000-0703 in Perl
Summary
by MITRE
suidperl (aka sperl) does not properly cleanse the escape sequence "~!" before calling /bin/mail to send an error report, which allows local users to gain privileges by setting the "interactive" environmental variable and calling suidperl with a filename that contains the escape sequence.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 12/07/2024
The vulnerability identified as CVE-2000-0703 resides within the suidperl utility, commonly known as sperl, which represents a critical security flaw in Unix-like operating systems. This utility operates with elevated privileges due to its setuid bit, allowing it to execute with the permissions of the file owner rather than the user who invoked it. The flaw specifically manifests when suidperl processes error reporting through the /bin/mail command, creating an environment where malicious input can be exploited to escalate privileges. The vulnerability stems from insufficient sanitization of escape sequences, particularly the "~!" sequence, which is commonly used in mail systems to indicate interactive mode or special handling of message content. When a local user sets the "interactive" environmental variable and invokes suidperl with a filename containing the problematic escape sequence, the system's privilege escalation mechanism becomes exploitable.
The technical exploitation of this vulnerability follows a well-defined pattern that leverages the interaction between environment variables and command execution. The suidperl utility, when processing files with the specified escape sequence in their names, fails to properly filter or escape these sequences before passing them to the mail command. This oversight creates a path where user-controlled input can influence the behavior of the mail utility in ways that were not intended. The escape sequence "~!" when processed by mail can trigger interactive mode or command execution within the mail system, potentially allowing attackers to inject shell commands or manipulate the mail delivery process. The interaction between the setuid environment and the vulnerable mail command execution creates a privilege escalation vector that bypasses normal access controls and allows local users to execute code with elevated privileges.
The operational impact of this vulnerability extends beyond simple privilege escalation, as it represents a fundamental flaw in how setuid utilities handle user input and external command invocation. Local users who can execute suidperl with controlled filenames can effectively bypass the normal security boundaries that protect system resources and user data. This vulnerability directly violates the principle of least privilege by allowing unauthorized privilege elevation, potentially enabling attackers to access sensitive system files, modify configurations, or establish persistent access. The attack surface is particularly concerning because it requires minimal prerequisites - simply having the ability to execute suidperl and control filenames, which is often possible in shared or multi-user environments. The vulnerability can be exploited to gain root access or other high-privilege accounts, making it a severe threat to system integrity and security.
Mitigation strategies for CVE-2000-0703 must address both the immediate exploitation vector and the underlying design flaw in the suidperl utility. The most effective approach involves implementing proper input sanitization and escaping of special characters before invoking external commands, particularly those with setuid privileges. Security practitioners should disable or remove suidperl from systems where it is not strictly required, as the utility represents a legacy component with known security issues. The implementation of proper environment variable handling and input validation mechanisms can prevent the propagation of malicious escape sequences into system commands. Organizations should also consider implementing privilege separation techniques that avoid the use of setuid binaries for utilities that can be replaced with safer alternatives. This vulnerability aligns with CWE-78 and CWE-20 categories, representing command injection and improper input validation flaws respectively, and can be mapped to ATT&CK technique T1068 which covers privilege escalation through local exploits. Regular security audits should include checking for the presence of setuid utilities that are vulnerable to similar input handling issues, and system administrators should maintain updated security patches that address these legacy vulnerabilities.