CVE-2019-16161 in Onigmo
Summary
by MITRE
Onigmo through 6.2.0 has a NULL pointer dereference in onig_error_code_to_str because of fetch_token in regparse.c.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 12/18/2023
The vulnerability identified as CVE-2019-16161 affects the Onigmo regular expression library version 6.2.0 and earlier, representing a critical NULL pointer dereference flaw that can lead to application crashes and potential denial of service conditions. This issue originates from the onig_error_code_to_str function within the library's error handling mechanism, specifically triggered by improper token processing during regular expression parsing operations. The root cause lies in the fetch_token function implementation within regparse.c, where the code fails to properly validate pointer references before dereferencing them, creating a scenario where a NULL value can be accessed leading to system instability.
The technical flaw manifests when the regular expression parser encounters malformed or specially crafted input patterns that cause the fetch_token function to return a NULL pointer which is then subsequently dereferenced by onig_error_code_to_str. This vulnerability falls under CWE-476 which specifically addresses NULL pointer dereference conditions, and represents a classic example of improper input validation in parsing components. The flaw exists in the library's error reporting pathway rather than in the core parsing logic itself, making it particularly insidious as it can be triggered even when the regular expression itself is syntactically valid but contains edge cases that cause internal state corruption.
From an operational impact perspective, this vulnerability presents significant risks to applications that rely on Onigmo for pattern matching operations, particularly those handling untrusted input data such as web applications, network intrusion detection systems, or any software that processes user-supplied regular expressions. The NULL pointer dereference can result in immediate application crashes, potentially allowing attackers to perform denial of service attacks against services that depend on this library. In more severe scenarios, if the library is used in a context where crashes can be exploited for memory corruption or information disclosure, the impact could extend beyond simple service disruption to more serious security implications. The vulnerability is particularly concerning in environments where regular expressions are processed from external sources without proper sanitization.
Mitigation strategies for CVE-2019-16161 should prioritize immediate patching of the Onigmo library to version 6.2.1 or later, where the NULL pointer dereference has been addressed through proper pointer validation in the fetch_token function. Organizations should implement input validation measures that sanitize all regular expression patterns before processing, particularly in applications that accept user input for pattern matching operations. Network segmentation and application isolation can help limit the impact of potential exploitation attempts, while monitoring systems should be configured to detect unusual application crash patterns that may indicate exploitation attempts. Additionally, implementing proper error handling and graceful degradation mechanisms in applications using Onigmo can help prevent complete service disruption even if the vulnerability is exploited, aligning with ATT&CK technique T1499.1 which addresses denial of service through resource exhaustion or application instability. The fix demonstrates the importance of proper defensive programming practices in parsing components and highlights the need for thorough testing of edge cases in regular expression libraries.