CVE-2016-9643 in tvOS
Summary
by MITRE
The regex code in Webkit 2.4.11 allows remote attackers to cause a denial of service (memory consumption) as demonstrated in a large number of ($ (open parenthesis and dollar) followed by {-2,16} and a large number of +) (plus close parenthesis).
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Analysis
by VulDB Data Team • 11/22/2022
The vulnerability identified as CVE-2016-9643 represents a critical denial of service flaw within the WebKit rendering engine version 2.4.11. This issue specifically targets the regular expression processing functionality that forms a fundamental component of web browser security and text parsing capabilities. The flaw manifests when the regex engine encounters malformed patterns that trigger excessive memory consumption during pattern compilation and execution phases, ultimately leading to system resource exhaustion and potential application instability.
The technical implementation of this vulnerability exploits a specific pattern construct involving the combination of open parenthesis, dollar sign, and quantifiers with large ranges. The malicious pattern structure ($ (open parenthesis and dollar) followed by {-2,16} and a large number of +) (plus close parenthesis) creates a recursive backtracking scenario that causes the regex engine to consume disproportionate amounts of memory. This pattern leverages the backtracking capabilities of the regular expression engine in a way that exponentially increases memory allocation requirements, creating a resource exhaustion condition that can be triggered through simple user input manipulation.
The operational impact of this vulnerability extends beyond simple service disruption as it can be exploited remotely by attackers to cause denial of service against web applications and browsers that utilize WebKit 2.4.11. The memory consumption behavior creates a predictable resource exhaustion attack vector that can be amplified through carefully crafted input sequences, making it particularly dangerous in environments where memory resources are constrained or where the target system has limited capacity to handle such resource demands. This vulnerability directly affects web applications and browsers that depend on the affected WebKit version, potentially compromising availability and accessibility of services.
Mitigation strategies for this vulnerability require immediate patching of affected WebKit versions to the latest stable releases that contain fixes for the regex engine backtracking issues. Organizations should implement input validation and sanitization measures to prevent malicious regex patterns from reaching the parsing engine, while also monitoring for unusual memory consumption patterns that might indicate exploitation attempts. The vulnerability aligns with CWE-129 and CWE-131 categories related to improper handling of regular expressions and insufficient resource management, and corresponds to ATT&CK techniques involving resource exhaustion and denial of service attacks. System administrators should also consider implementing network-level protections and rate limiting to reduce the impact of potential exploitation attempts while patches are deployed.