CVE-2018-17142 in HTML Package
Summary
by MITRE
The html package (aka x/net/html) through 2018-09-17 in Go mishandles <math><template><mo><template>, leading to a "panic: runtime error" in parseCurrentToken in parse.go during an html.Parse call.
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Analysis
by VulDB Data Team • 05/16/2023
The vulnerability identified as CVE-2018-17142 affects the html package within the Go programming language ecosystem, specifically within the x/net/html module. This issue represents a critical runtime error that occurs during HTML parsing operations, demonstrating a fundamental flaw in how the parser handles nested template elements within mathematical expressions. The vulnerability manifests when processing malformed HTML containing the specific sequence of tags <math><template><mo><template>, which triggers an unexpected panic condition within the parsing logic. This particular combination of elements creates a parsing state that the Go html package cannot properly handle, leading to a runtime panic that terminates the application process.
The technical root cause of this vulnerability lies within the parseCurrentToken function located in parse.go, which fails to properly manage the parsing state when encountering nested template elements within mathematical contexts. This flaw represents a classic case of improper state management and inadequate error handling within the HTML parser implementation. The vulnerability is classified under CWE-248, which deals with an exception is thrown for an unspecified reason, and aligns with ATT&CK technique T1203, which involves exploiting application vulnerabilities through malformed input processing. The parsing logic does not adequately validate the nesting structure of elements, particularly when template tags are used within mathematical expressions, leading to an inconsistent internal state that causes the runtime to panic.
The operational impact of this vulnerability is severe as it can lead to application crashes and potential denial of service conditions in systems that process untrusted HTML content. Any application utilizing the Go html package for parsing user-generated content or external HTML sources becomes vulnerable to this attack vector, making it particularly dangerous in web applications, content management systems, and any environment where HTML parsing is performed on potentially malicious input. The vulnerability affects all versions of the Go html package released prior to the patch date of 2018-09-17, creating a window of exposure for numerous applications that depend on this parsing functionality. Attackers can exploit this by crafting malicious HTML payloads containing the specific tag sequence, causing targeted applications to crash and potentially allowing for more sophisticated attacks if the application does not properly handle the panic conditions.
Mitigation strategies for CVE-2018-17142 involve immediate patching of the Go html package to the version released after September 17, 2018, which contains the necessary fixes for proper handling of nested template elements. Organizations should also implement comprehensive input validation and sanitization measures, particularly for HTML content that originates from untrusted sources. The implementation of proper error handling mechanisms around HTML parsing operations can help prevent application crashes from propagating and should include graceful degradation when malformed content is encountered. Additionally, security teams should conduct thorough code reviews focusing on parsing logic and ensure that all applications utilizing the html package are updated to versions that address this specific panic condition. The vulnerability highlights the importance of robust error handling in parsing libraries and demonstrates the critical need for thorough testing of edge cases in HTML processing systems, particularly when dealing with complex nested structures and mathematical expressions within HTML documents.