CVE-2022-28366 in HtmlUnit-Neko
Summary
by MITRE • 04/22/2022
Certain Neko-related HTML parsers allow a denial of service via crafted Processing Instruction (PI) input that causes excessive heap memory consumption. In particular, this issue exists in HtmlUnit-Neko through 2.26, and is fixed in 2.27. This issue also exists in CyberNeko HTML through 1.9.22 (also affecting OWASP AntiSamy before 1.6.6), but 1.9.22 is the last version of CyberNeko HTML. NOTE: this may be related to CVE-2022-24939.
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Analysis
by VulDB Data Team • 04/28/2022
The vulnerability described in CVE-2022-28366 represents a significant denial of service weakness affecting HTML parsing libraries that utilize Neko-related parsers. This issue specifically targets the processing instruction (PI) handling within these parsers, creating a condition where maliciously crafted PI input can trigger excessive heap memory consumption. The vulnerability affects multiple components including HtmlUnit-Neko versions through 2.26 and CyberNeko HTML versions through 1.9.22, with the latter being the final release of the CyberNeko HTML library. The problem manifests as a resource exhaustion attack that can effectively crash applications or render them unresponsive through memory allocation abuse.
The technical flaw stems from inadequate input validation and memory management within the parser's handling of processing instructions. When a parser encounters specially crafted PI data, it fails to properly limit memory allocation or implement defensive mechanisms against recursive or exponentially growing memory consumption patterns. This allows an attacker to construct PI sequences that cause the parser to allocate increasingly large amounts of heap memory, eventually exhausting available system resources. The vulnerability operates at the parser level where processing instructions are typically used to provide metadata about the document structure, but in this case, the malicious input causes the parser to behave in an uncontrolled memory allocation pattern that can grow rapidly with each processed instruction.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect entire application availability and system stability. Applications relying on affected parsers for HTML processing, particularly those handling untrusted user input or external web content, become vulnerable to memory exhaustion attacks that can be executed with relatively simple input payloads. This makes the vulnerability particularly dangerous in web applications, content management systems, or any software that processes HTML content from potentially malicious sources. The attack surface is broad given that these parsers are commonly used in web scraping tools, security scanners, and content filtering applications, making the potential for widespread exploitation significant.
Security mitigations for this vulnerability primarily involve upgrading to patched versions of the affected libraries, specifically HtmlUnit-Neko 2.27 and ensuring CyberNeko HTML is updated to a version beyond 1.9.22. Organizations should also implement input validation measures that limit the size and complexity of processing instructions in parsed content, particularly when dealing with external or untrusted input. Additionally, memory monitoring and resource limiting should be implemented at the application level to detect and prevent excessive memory consumption patterns. The vulnerability aligns with CWE-400, which addresses unchecked resource consumption, and relates to ATT&CK technique T1499.004 for resource exhaustion attacks, demonstrating how parser-based vulnerabilities can be leveraged for denial of service operations. The relationship to CVE-2022-24939 suggests this may be part of a broader class of memory handling issues in Neko-based HTML parsers that require comprehensive security review and remediation across affected codebases.