CVE-2005-0156 in Perl
Summary
by MITRE
Buffer overflow in the PerlIO implementation in Perl 5.8.0, when installed with setuid support (sperl), allows local users to execute arbitrary code by setting the PERLIO_DEBUG variable and executing a Perl script whose full pathname contains a long directory tree.
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Analysis
by VulDB Data Team • 07/03/2024
The vulnerability described in CVE-2005-0156 represents a critical buffer overflow flaw within Perl's PerlIO implementation that specifically affects Perl 5.8.0 installations configured with setuid support. This issue arises from the insecure handling of environment variables within the Perl interpreter's input/output subsystem, creating a pathway for privilege escalation attacks. The vulnerability is particularly dangerous because it leverages the setuid perl binary (sperl) which runs with elevated privileges, making any successful exploitation potentially devastating for system security.
The technical flaw manifests when the PERLIO_DEBUG environment variable is set and a Perl script is executed with a full pathname containing an excessively long directory tree structure. The PerlIO implementation fails to properly validate the length of the debug information being processed, leading to a buffer overflow condition in memory. This overflow occurs during the handling of the debug variable which is designed to provide internal debugging information about the PerlIO subsystem. The vulnerability specifically targets the memory layout of the Perl interpreter when processing file paths, particularly when these paths exceed the allocated buffer space in the debug output handling code.
The operational impact of this vulnerability is severe as it allows local users to execute arbitrary code with the privileges of the setuid perl binary. Since sperl typically runs with root privileges, successful exploitation could result in complete system compromise. Attackers need only set the PERLIO_DEBUG environment variable and execute a malicious script with a sufficiently long pathname to trigger the buffer overflow. This creates a low-barrier attack vector that does not require network connectivity or external exploitation mechanisms, making it particularly dangerous in multi-user environments where local privilege escalation is a significant concern. The vulnerability also aligns with attack patterns documented in the ATT&CK framework under privilege escalation techniques, specifically targeting the use of setuid binaries as initial access points.
Mitigation strategies for this vulnerability should focus on immediate patching of Perl installations to versions that address the buffer overflow in the PerlIO implementation. System administrators should ensure that sperl is not installed or properly configured to avoid unnecessary setuid privileges. The environment variable PERLIO_DEBUG should be restricted or sanitized in production environments, and all Perl scripts should be validated for safe pathname handling. Additionally, implementing proper input validation and bounds checking in the Perl interpreter's file path processing code would prevent similar issues. Organizations should also consider monitoring for suspicious environment variable usage and PATH manipulation that could indicate exploitation attempts, aligning with security best practices outlined in CWE-121 and CWE-122 categories that address buffer overflow conditions and memory safety violations.