CVE-2016-1283 in PCRE
Summary
by MITRE
The pcre_compile2 function in pcre_compile.c in PCRE 8.38 mishandles the /((?:F?+(?:^(?(R)a+\"){99}-))(?J)(?'R'(?'R'<((?'RR'(?'R'\){97)?J)?J)(?'R'(?'R'\){99|(:(?|(?'R')(\k'R')|((?'R')))H'R'R)(H'R))))))/ pattern and related patterns with named subgroups, which allows remote attackers to cause a denial of service (heap-based buffer overflow) or possibly have unspecified other impact via a crafted regular expression, as demonstrated by a JavaScript RegExp object encountered by Konqueror.
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Analysis
by VulDB Data Team • 07/02/2022
The vulnerability identified as CVE-2016-1283 resides within the PCRE (Perl Compatible Regular Expressions) library version 8.38, specifically within the pcre_compile2 function located in pcre_compile.c. This flaw represents a critical heap-based buffer overflow condition that occurs when processing certain complex regular expression patterns containing named subgroups and recursive constructs. The vulnerability manifests through the improper handling of nested patterns that utilize conditional assertions, recursive references, and named capture groups in a specific combination that triggers memory corruption during the compilation phase of regular expressions.
The technical exploitation of this vulnerability occurs when the pcre_compile2 function encounters a crafted regular expression pattern that contains deeply nested structures with named subgroups. The pattern structure involves recursive references using the (?R) construct combined with named capture groups and conditional assertions that create an exponential backtracking scenario. When the library attempts to compile this specific pattern, it fails to properly validate the memory allocation required for storing the compiled regular expression structure, leading to a heap-based buffer overflow. This overflow can potentially be leveraged by remote attackers to execute arbitrary code or cause a denial of service condition.
The operational impact of CVE-2016-1283 extends beyond simple denial of service to potentially enable remote code execution depending on the system configuration and memory layout. The vulnerability affects web browsers and applications that utilize the PCRE library for regular expression processing, including Konqueror web browser as demonstrated in the original exploit. When exploited, this vulnerability can cause applications to crash or behave unpredictably, potentially allowing attackers to inject malicious code into the target system. The flaw is particularly dangerous in web applications where user input is processed through regular expressions, as it can be triggered through crafted input that appears benign but contains the malicious pattern structure.
This vulnerability maps to CWE-121 Heap-based Buffer Overflow, which is classified as a memory safety error that occurs when more data is written to a heap buffer than it can hold, typically due to inadequate bounds checking. The attack pattern follows the techniques described in MITRE ATT&CK framework under T1059.007 for Scripting and T1499.004 for Endpoint Denial of Service. The vulnerability demonstrates a classic example of exponential backtracking in regular expression engines where the complexity of pattern matching grows exponentially with input size, leading to resource exhaustion and memory corruption. Organizations using PCRE-based systems should immediately apply patches to mitigate this vulnerability, as the exploitation can occur through web-based inputs without requiring any special privileges from the attacker. The fix involves proper bounds checking and memory allocation validation within the pcre_compile2 function to prevent the creation of malformed compiled regular expression structures that could lead to heap corruption.