CVE-2018-17846 in Google
Summary
by MITRE
The html package (aka x/net/html) through 2018-09-25 in Go mishandles <table><math><select><mi><select></table>, leading to an infinite loop during an html.Parse call because inSelectIM and inSelectInTableIM do not comply with a specification.
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Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2018-17846 affects the html package within the Go programming language ecosystem, specifically versions released through September 25, 2018. This issue resides in the x/net/html module which serves as the HTML parsing implementation for Go applications. The flaw manifests during the parsing of malformed HTML content that contains nested elements in a specific sequence involving table, math, select, and mi elements. The vulnerability represents a classic case of improper state machine handling within HTML parsing logic, where the parser fails to correctly transition between different parsing states when encountering this particular element combination.
The technical root cause of this vulnerability stems from the implementation of two specific parsing states within the HTML parser: inSelectIM and inSelectInTableIM. These states are responsible for managing the parsing context when elements are encountered within table and select contexts. When the parser encounters the sequence <table><math><select><mi><select></table>, it enters an infinite loop because these two parsing states fail to properly handle the element transitions according to the HTML specification. The parser becomes trapped in a loop where it continuously checks for valid state transitions without ever progressing to a completion state, effectively causing a denial of service condition. This behavior violates the expected parsing semantics defined in the HTML5 specification and represents a failure in proper state management within the parser implementation.
The operational impact of this vulnerability is significant for any Go application that processes untrusted HTML content through the html package. An attacker could craft malicious HTML payloads containing the specific element sequence that triggers the infinite loop, leading to resource exhaustion and application unresponsiveness. This creates a reliable denial of service condition that can be exploited across any system using affected versions of Go, making it particularly dangerous in web applications, content management systems, or any service that accepts and parses user-generated HTML content. The vulnerability affects the core parsing functionality and can impact applications ranging from web servers to command-line tools that process HTML documents, with potential cascading effects on system availability and performance.
This vulnerability aligns with CWE-835, which describes the weakness of infinite loops in software implementations, and demonstrates how improper handling of parsing state machines can lead to denial of service conditions. From an attack perspective, this issue maps to ATT&CK technique T1499.004, which covers network disruption through resource exhaustion, and T1210, which involves exploitation of vulnerabilities in parsing libraries. The fix for this vulnerability required modifications to the HTML parser's state transition logic to ensure proper handling of the element sequence and correct state management during parsing operations. Organizations should immediately update to Go versions that include the patched html package, typically those released after the vulnerability disclosure, to mitigate this risk and prevent potential exploitation in production environments.