CVE-2009-3626 in Perl
Summary
by MITRE
Perl 5.10.1 allows context-dependent attackers to cause a denial of service (application crash) via a UTF-8 character with a large, invalid codepoint, which is not properly handled during a regular-expression match.
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Analysis
by VulDB Data Team • 10/02/2025
The vulnerability identified as CVE-2009-3626 represents a significant denial of service weakness within Perl 5.10.1's regular expression engine. This flaw specifically manifests when the application encounters UTF-8 characters containing large invalid codepoints during pattern matching operations. The vulnerability falls under the category of improper input validation and memory handling within text processing functions, creating a scenario where legitimate text processing operations can trigger unexpected application termination.
The technical mechanism behind this vulnerability involves the interaction between Perl's UTF-8 handling routines and its regular expression matching engine. When a UTF-8 sequence containing an invalid codepoint is processed within a regex pattern, the system fails to properly validate the character boundaries and codepoint ranges. This improper handling leads to memory access violations or buffer overflows during the matching process, ultimately causing the Perl interpreter to crash and terminate unexpectedly. The vulnerability is context-dependent because it requires specific UTF-8 character sequences that trigger the malformed codepoint handling path within the regex engine.
From an operational perspective, this vulnerability presents a serious threat to systems that process untrusted text input through Perl applications. Attackers can craft malicious UTF-8 sequences that will cause any Perl application performing regular expression matching to crash, effectively creating a denial of service condition. This affects web applications, text processing utilities, and any system where Perl handles user-provided content through regex operations. The impact extends beyond simple service disruption to potentially enable more sophisticated attack vectors if combined with other vulnerabilities in the application stack. The vulnerability demonstrates poor error handling practices in text encoding validation, which aligns with CWE-129, which addresses improper handling of buffer overflows and memory access violations in input validation.
The mitigation strategies for this vulnerability primarily involve upgrading to a patched version of Perl where the UTF-8 handling and regex engine have been corrected to properly validate codepoint ranges and handle invalid sequences gracefully. System administrators should also implement input validation at application boundaries to sanitize UTF-8 sequences before they reach the regex processing layer. Additionally, deploying intrusion detection systems that can identify malformed UTF-8 sequences in network traffic provides an additional defensive layer. Organizations should consider implementing proper error handling and graceful degradation mechanisms within their Perl applications to prevent complete application crashes from single malformed inputs. This vulnerability highlights the importance of robust text encoding validation and proper error handling in security-critical applications, aligning with ATT&CK technique T1499.004 for resource exhaustion and T1059.007 for command and scripting interpreters. The issue also demonstrates how seemingly benign text processing operations can become security risks when proper input validation and error handling are not implemented.