CVE-2006-7226 in Red Hat
Summary
by MITRE
Perl-Compatible Regular Expression (PCRE) library before 6.7 does not properly calculate the compiled memory allocation for regular expressions that involve a quantified "subpattern containing a named recursion or subroutine reference," which allows context-dependent attackers to cause a denial of service (error or crash).
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Analysis
by VulDB Data Team • 07/31/2019
The vulnerability identified as CVE-2006-7226 affects the Perl-Compatible Regular Expression library version 6.6 and earlier, representing a critical memory management flaw that can be exploited to cause denial of service conditions. This issue specifically manifests when processing regular expressions containing quantified subpatterns with named recursion or subroutine references, creating a scenario where the library fails to accurately compute memory requirements during compilation. The flaw exists in the memory allocation algorithm that governs how PCRE handles complex recursive patterns, making it susceptible to malformed input that can trigger excessive memory consumption or invalid memory access patterns.
The technical root cause of this vulnerability lies in the improper calculation of memory allocation for compiled regular expressions when dealing with recursive constructs. When a regular expression contains a quantified subpattern that references a named recursion or subroutine, the PCRE library's internal memory allocator does not correctly account for the memory needed to store the compiled representation of these recursive structures. This miscalculation can result in insufficient memory allocation for the compiled pattern, leading to buffer overflows, memory corruption, or invalid memory access errors that cause the application using PCRE to crash or behave unpredictably. The vulnerability is context-dependent, meaning its exploitation requires specific patterns in the input regular expressions that trigger the faulty memory calculation logic.
The operational impact of this vulnerability extends beyond simple application crashes, as it can be leveraged by malicious actors to perform denial of service attacks against systems relying on PCRE for regular expression processing. Applications that process user-supplied regular expressions, such as web applications, network intrusion detection systems, or any software utilizing PCRE for pattern matching, become vulnerable to this attack vector. The vulnerability affects systems where PCRE is used for input validation, log parsing, or text processing tasks where regular expressions are dynamically constructed or received from untrusted sources. Attackers can craft specific regular expressions that, when processed by the vulnerable PCRE library, will cause memory allocation failures leading to application instability or complete system crashes.
Mitigation strategies for this vulnerability require immediate patching of affected PCRE installations to version 6.7 or later, where the memory allocation calculation has been corrected to properly handle recursive subpatterns. System administrators should also implement input validation measures to restrict the complexity and length of regular expressions processed by applications, particularly those accepting user input. Additionally, deploying intrusion prevention systems that can detect and block suspicious regular expression patterns may provide additional defense layers. Organizations should also consider implementing memory protection mechanisms such as stack canaries, address space layout randomization, and heap-based memory corruption detection to limit the impact of potential exploitation attempts. This vulnerability aligns with CWE-129, which addresses improper validation of length of input buffers, and relates to ATT&CK technique T1059.007 for execution through scripting languages, particularly when regular expressions are used in application logic processing.