CVE-2017-7244 in PCRE
Summary
by MITRE
The _pcre32_xclass function in pcre_xclass.c in libpcre1 in PCRE 8.40 allows remote attackers to cause a denial of service (invalid memory read) via a crafted file.
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Analysis
by VulDB Data Team • 11/15/2022
The vulnerability identified as CVE-2017-7244 represents a critical denial of service flaw within the Perl Compatible Regular Expressions library version 8.40. This issue specifically affects the _pcre32_xclass function located in the pcre_xclass.c source file, which forms part of the libpcre1 component. The vulnerability manifests when processing malformed input data through regular expression parsing mechanisms, creating a scenario where an attacker can trigger an invalid memory read operation that ultimately leads to system instability or complete service disruption.
The technical exploitation of this vulnerability occurs through careful crafting of input files that contain specially constructed regular expressions designed to manipulate the internal state of the pcre32_xclass function. When the library processes these malformed patterns, the function fails to properly validate input boundaries, leading to memory access violations that result in segmentation faults or similar system crashes. This behavior stems from inadequate bounds checking within the regular expression engine's handling of character class matching operations, particularly when dealing with 32-bit character sequences.
From an operational impact perspective, this vulnerability poses significant risks to systems that rely heavily on regular expression processing for security filtering, data validation, or content parsing tasks. Applications utilizing libpcre1 for pattern matching, including web application firewalls, intrusion detection systems, log analyzers, and content management platforms, become vulnerable to remote denial of service attacks. The vulnerability's remote exploitability means that attackers can trigger the condition without requiring local access, making it particularly dangerous in networked environments where regular expression processing is common.
The underlying flaw aligns with CWE-125: "Out-of-bounds Read" and demonstrates characteristics consistent with ATT&CK technique T1499.004: "Endpoint Denial of Service" where adversaries target application vulnerabilities to disrupt service availability. This vulnerability exemplifies how seemingly benign parsing operations can become attack vectors when proper input validation and memory boundary checks are absent. The issue affects not only individual applications but potentially entire systems that depend on the PCRE library for text processing capabilities.
Organizations should implement immediate mitigation strategies including updating to PCRE version 8.41 or later where this vulnerability has been patched, deploying input validation measures to filter suspicious regular expression patterns, and implementing monitoring for unusual memory access patterns or service disruptions. Additionally, system administrators should consider isolating applications that process untrusted regular expression data and implementing rate limiting or sandboxing mechanisms to prevent exploitation attempts. The vulnerability underscores the importance of maintaining current security patches and conducting regular vulnerability assessments of third-party libraries used in critical systems.