CVE-2016-9954 in Irregex Package
Summary
by MITRE
The backtrack compilation code in the Irregex package (aka IrRegular Expressions) before 0.9.6 for Scheme allows remote attackers to cause a denial of service (memory consumption) via a crafted regular expression with a repeating pattern.
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Analysis
by VulDB Data Team • 12/02/2022
The CVE-2016-9954 vulnerability resides within the Irregex package, also known as IrRegular Expressions, a Scheme-based regular expression library that has been widely adopted in various applications and systems. This particular flaw affects versions prior to 0.9.6 and represents a significant security concern due to its potential to enable remote attackers to execute denial of service attacks through carefully crafted malicious regular expressions. The vulnerability specifically targets the backtrack compilation code within the package, which is responsible for processing and compiling regular expression patterns into executable code structures.
The technical flaw manifests when the backtrack compilation mechanism encounters regular expressions containing repeating patterns that trigger excessive memory consumption during the compilation phase. This occurs because the implementation fails to properly handle certain recursive or nested pattern structures that cause the compiler to enter into exponential time and space complexity scenarios. When an attacker submits a maliciously constructed regular expression, the backtrack engine attempts to explore all possible matching paths through the pattern, leading to unbounded memory growth as the system attempts to maintain state information for each potential backtracking path. This behavior represents a classic example of a resource exhaustion vulnerability where computational resources become consumed at an unsustainable rate.
The operational impact of CVE-2016-9954 extends beyond simple service disruption as it can affect any system or application that utilizes the vulnerable Irregex package for pattern matching operations. Attackers can leverage this vulnerability to consume all available memory on the target system, causing applications to crash, become unresponsive, or force system administrators to restart services. The vulnerability is particularly dangerous in multi-tenant environments or web applications where regular expressions are processed based on user input, as it allows attackers to target the system without requiring authentication or specialized privileges. This makes it a prime candidate for exploitation in distributed denial of service scenarios and can significantly impact system availability and performance.
Mitigation strategies for this vulnerability primarily involve upgrading to version 0.9.6 or later of the Irregex package, which includes fixes for the backtrack compilation logic that prevent the excessive memory consumption patterns. Organizations should also implement input validation and sanitization measures to filter potentially malicious regular expressions before they reach the compilation phase, particularly when processing user-provided patterns. The vulnerability aligns with CWE-400, which classifies it as an "Uncontrolled Resource Consumption" issue, and can be mapped to ATT&CK technique T1499.004, "Application Exhaustion Flood," as it involves resource consumption attacks targeting application-level processing. Additional protective measures include implementing resource limits and timeouts for pattern compilation operations, monitoring memory usage patterns, and conducting regular security assessments of all components that utilize regular expression processing capabilities to prevent similar vulnerabilities from being exploited in other systems.