CVE-2019-9169 in C Library
Summary
by MITRE
In the GNU C Library (aka glibc or libc6) through 2.29, proceed_next_node in posix/regexec.c has a heap-based buffer over-read via an attempted case-insensitive regular-expression match.
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Analysis
by VulDB Data Team • 07/19/2023
The vulnerability identified as CVE-2019-9169 represents a critical heap-based buffer over-read flaw within the GNU C Library implementation of regular expression matching functionality. This issue affects glibc versions through 2.29 and specifically impacts the proceed_next_node function located in posix/regexec.c. The vulnerability manifests during case-insensitive regular expression matching operations, where the library fails to properly validate buffer boundaries when processing pattern matching algorithms. The flaw stems from inadequate bounds checking in the regular expression engine's internal state management, particularly when handling character class matching with case insensitivity enabled.
The technical exploitation of this vulnerability occurs when an attacker crafts a malicious regular expression pattern that triggers the flawed code path within the proceed_next_node function. During execution, the library attempts to read beyond the allocated heap memory boundaries while processing case-insensitive matching operations, potentially exposing sensitive data or enabling arbitrary code execution depending on memory layout and exploitation conditions. This type of buffer over-read vulnerability falls under CWE-125, which specifically addresses out-of-bounds read conditions that can lead to information disclosure, system instability, or potential privilege escalation. The vulnerability's impact is amplified by the widespread use of glibc across Linux systems and applications that rely on standard C library functions for text processing.
The operational implications of CVE-2019-9169 extend beyond simple information disclosure, as it represents a potential vector for remote code execution in applications that process untrusted regular expressions. Systems utilizing affected glibc versions are vulnerable to attacks targeting web applications, network services, and any software that employs regular expression matching with user-provided input. The vulnerability affects the core POSIX regular expression implementation and can be triggered through various attack vectors including web application input validation, network protocol parsing, and system logging functions that process user-supplied patterns. This flaw aligns with ATT&CK technique T1059.007 for scripting languages and T1211 for exploitation for defense evasion, as the vulnerability could be leveraged to execute arbitrary code or maintain persistence through crafted regular expressions.
Mitigation strategies for CVE-2019-9169 require immediate system updates to glibc version 2.30 or later, which contain the necessary patches to address the buffer over-read condition. System administrators should prioritize patching all affected systems, particularly those running web servers, network services, and applications that process untrusted regular expression input. Additional protective measures include implementing input validation and sanitization for all regular expression operations, limiting the complexity of user-provided patterns, and deploying intrusion detection systems that monitor for suspicious regular expression patterns. Organizations should also consider implementing runtime protections such as address space layout randomization and stack canaries to reduce the effectiveness of potential exploitation attempts. The vulnerability demonstrates the critical importance of maintaining up-to-date system libraries and highlights the need for comprehensive vulnerability management programs that address both known and emerging threats in core system components.