CVE-2017-12837 in Perl
Summary
by MITRE
Heap-based buffer overflow in the regular expression compiler in PERL before 5.24.3-RC1 and 5.26.x before 5.26.1-RC1 allows remote attackers to cause a denial of service (crash) via a crafted regular expression with the case-insensitive modifier.
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Analysis
by VulDB Data Team • 01/13/2021
The heap-based buffer overflow vulnerability identified as CVE-2017-12837 resides within the regular expression compiler of the perl programming language, representing a critical security flaw that affects multiple versions of the software. This vulnerability specifically manifests when perl processes regular expressions that contain the case-insensitive modifier, creating a condition where maliciously crafted patterns can trigger memory corruption. The flaw exists in the heap memory management system of perl's regex engine, where insufficient bounds checking allows an attacker to write beyond allocated memory boundaries, resulting in unpredictable behavior and system instability.
The technical implementation of this vulnerability stems from improper handling of memory allocation during the compilation phase of regular expressions that utilize case-insensitive matching. When perl encounters a specially crafted regex pattern with the case-insensitive modifier, the internal compiler fails to properly validate the memory requirements for storing intermediate compilation results. This leads to a situation where the program attempts to write data beyond the allocated heap buffer space, causing memory corruption that manifests as a crash or denial of service condition. The vulnerability is classified under CWE-121 as a heap-based buffer overflow, which is a well-known weakness in memory management systems where insufficient bounds checking allows for memory corruption.
The operational impact of this vulnerability extends beyond simple denial of service, as it can be exploited by remote attackers to disrupt services that rely on perl's regular expression processing capabilities. Systems that process user input through perl applications, such as web applications, network security tools, or automated processing systems, become vulnerable to exploitation. The vulnerability is particularly concerning in environments where perl is used to parse untrusted input from external sources, as attackers can craft malicious regular expressions that trigger the overflow condition. This can result in complete service disruption, system crashes, or potentially more severe consequences if the application continues to execute after the initial crash. The ATT&CK framework categorizes this vulnerability under T1499.004 for Network Denial of Service and T1059.007 for Command and Scripting Interpreter, as it enables attackers to disrupt system operations through malformed input processing.
Mitigation strategies for CVE-2017-12837 primarily focus on immediate software updates and input validation measures. Organizations should prioritize upgrading to perl versions 5.24.3-RC1 or later, or 5.26.1-RC1 or later, which contain patches addressing the heap buffer overflow condition. Additionally, implementing strict input validation and sanitization measures can help prevent exploitation by rejecting suspicious regular expression patterns before they reach the perl interpreter. System administrators should also consider implementing rate limiting and input length restrictions on applications that process user-supplied regex patterns, as this can prevent exploitation attempts that rely on large or complex patterns. Network monitoring solutions should be configured to detect unusual patterns of regex processing that might indicate exploitation attempts, while also maintaining proper logging of all perl application activities for forensic analysis purposes. The vulnerability demonstrates the importance of maintaining up-to-date software components and implementing robust input validation practices to prevent memory corruption exploits from compromising system integrity.