CVE-2018-17848 in Google
Summary
by MITRE
The html package (aka x/net/html) through 2018-09-25 in Go mishandles <math><template><mn><b></template>, leading to a "panic: runtime error" (index out of range) in (*insertionModeStack).pop in node.go, called from inHeadIM, during an html.Parse call.
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Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2018-17848 represents a critical runtime error in the Go programming language's html package, specifically within the x/net/html module. This issue manifests as a panic condition that occurs during HTML parsing operations, creating a potential denial of service scenario for applications relying on the standard library's HTML parsing capabilities. The vulnerability was present in versions of the html package released through September 25, 2018, and affects the core parsing functionality that many Go applications depend upon for processing HTML content.
The technical flaw stems from improper handling of nested HTML elements in a specific sequence involving mathematical and template tags. The problematic tag structure <math><template><mn><b></template> creates an unusual parsing scenario where the insertion mode stack management fails to properly account for the element hierarchy. During the html.Parse operation, the parser attempts to manipulate the insertion mode stack through the (*insertionModeStack).pop method in node.go, which subsequently triggers a "panic: runtime error" with an "index out of range" condition. This error occurs within the inHeadIM function, indicating that the parser's state management becomes corrupted during the processing of this particular HTML fragment.
The operational impact of this vulnerability extends beyond simple parsing failures, as it can lead to complete application crashes when malformed HTML input is processed through the affected Go applications. This represents a denial of service condition where malicious actors could potentially exploit this weakness by submitting carefully crafted HTML content that triggers the panic condition. The vulnerability affects any application using the standard Go html package for parsing HTML content, including web applications, scrapers, and any system processing user-generated HTML input. The runtime error occurs during the parsing phase, meaning that applications may not even reach their business logic before crashing, making this particularly dangerous in production environments where stability is paramount.
This vulnerability aligns with CWE-129, which addresses improper validation of array indices, and demonstrates the importance of robust input validation in parsing libraries. The issue also relates to ATT&CK technique T1499.004, which covers network denial of service attacks, as the panic condition can be leveraged to crash services through malformed input. The root cause reflects poor error handling in stack management operations and highlights the need for comprehensive boundary checking in parsing state machines. Organizations should immediately update to versions of Go that include the patched html package, typically Go 1.11.1 or later, to mitigate this risk. Additionally, implementing proper input sanitization and error handling around HTML parsing operations can provide additional defense in depth, ensuring that even if malformed content slips through, the application can gracefully handle the error rather than crashing completely.