CVE-2008-1927 in Perl
Summary
by MITRE
Double free vulnerability in Perl 5.8.8 allows context-dependent attackers to cause a denial of service (memory corruption and crash) via a crafted regular expression containing UTF8 characters. NOTE: this issue might only be present on certain operating systems.
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Analysis
by VulDB Data Team • 08/09/2019
The double free vulnerability identified as CVE-2008-1927 represents a critical memory corruption flaw within Perl 5.8.8's regular expression processing engine. This vulnerability manifests when the interpreter encounters crafted regular expressions containing UTF8 characters, creating a scenario where the same memory block gets freed twice during the execution lifecycle. The flaw stems from inadequate memory management within the regex engine's handling of multibyte character sequences, particularly when processing UTF8 encoded patterns that trigger specific internal state transitions.
The technical implementation of this vulnerability exploits the Perl interpreter's memory allocation and deallocation mechanisms during regex compilation and execution phases. When processing UTF8 characters within regular expressions, the interpreter's internal data structures become corrupted due to improper handling of reference counting for memory blocks allocated during pattern parsing. This double free condition occurs because the regex engine fails to properly track memory allocations when UTF8 sequences are processed in specific contexts, leading to a scenario where a memory block is deallocated twice by different code paths within the same execution flow. The vulnerability is context-dependent, meaning it only manifests under specific conditions involving UTF8 character handling within regex patterns, making it particularly challenging to detect and exploit consistently.
The operational impact of this vulnerability extends beyond simple denial of service to potentially enable more sophisticated attacks depending on the target environment. While the primary effect is memory corruption and system crashes, the double free condition creates opportunities for heap-based memory corruption that could theoretically be leveraged for arbitrary code execution in certain circumstances. The vulnerability affects systems running Perl 5.8.8 where UTF8 character processing is enabled, particularly impacting web applications and scripts that process user-supplied input through regular expressions. This makes it especially dangerous in environments where Perl is used for processing untrusted data such as web forms, API inputs, or file parsing operations. The conditional nature of the vulnerability means that exploitation success varies across different operating systems and Perl build configurations, with some platforms being more susceptible than others based on their memory management implementations.
Mitigation strategies for CVE-2008-1927 focus primarily on immediate patching and system hardening measures. The most effective solution involves upgrading to Perl 5.8.9 or later versions where the double free vulnerability has been addressed through improved memory management within the regex engine. System administrators should implement input validation and sanitization measures to prevent untrusted regex patterns from being processed, particularly when user input is involved in pattern construction. Additionally, deploying application-level firewalls and web application firewalls can help detect and block malicious regex patterns before they reach the Perl interpreter. The vulnerability aligns with CWE-415, which addresses double free conditions in memory management, and can be categorized under ATT&CK technique T1059.007 for script-based execution. Organizations should also consider implementing memory protection mechanisms such as stack canaries, address space layout randomization, and heap integrity checks to reduce the potential impact of exploitation attempts. Regular security assessments and vulnerability scanning should be conducted to identify systems running vulnerable Perl versions and ensure timely remediation of this and related memory corruption vulnerabilities.