CVE-2018-17847 in Google
Summary
by MITRE
The html package (aka x/net/html) through 2018-09-25 in Go mishandles <svg><template><desc><t><svg></template>, leading to a "panic: runtime error" (index out of range) in (*nodeStack).pop in node.go, called from (*parser).clearActiveFormattingElements, during an html.Parse call.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 05/19/2023
The vulnerability identified as CVE-2018-17847 represents a critical runtime error in the Go programming language's html package, specifically within the x/net/html module. This issue manifests when processing malformed HTML structures containing nested SVG elements with template and text nodes in a particular arrangement. The affected component is part of Go's standard library and is widely used for HTML parsing operations across numerous applications and services. The vulnerability stems from improper handling of nested HTML structures that combine SVG elements with template tags and text elements, creating a scenario where the internal node stack management fails catastrophically.
The technical flaw occurs within the nodeStack.pop method in the node.go file of the html package implementation. When the parser encounters the specific malformed HTML pattern <svg><template><desc><t><svg></template>, it triggers a sequence of operations that leads to an index out of range panic. This happens during the execution of (*parser).clearActiveFormattingElements function, which is responsible for maintaining proper stack management during HTML parsing. The parser's internal state management becomes corrupted when processing this particular combination of nested elements, causing the nodeStack to attempt accessing an invalid memory index. This runtime error demonstrates a classic buffer overflow condition in the parser's stack management logic, where insufficient bounds checking allows access to memory outside the allocated stack boundaries.
The operational impact of this vulnerability is significant for any Go application that processes untrusted HTML content through the html.Parse function. Attackers can exploit this weakness by providing maliciously crafted HTML input that triggers the specific parsing pattern, resulting in application crashes and potential denial of service conditions. The vulnerability affects the entire Go ecosystem since the html package is a fundamental component used across various web applications, content management systems, and web scraping tools. Applications relying on Go's HTML parsing capabilities for user input processing, web scraping, or content generation become vulnerable to this panic condition, potentially leading to service disruption and system instability. The vulnerability is particularly dangerous in web applications where user-provided HTML content is parsed without proper sanitization.
Mitigation strategies for CVE-2018-17847 should prioritize updating to patched versions of Go that contain the corrected html package implementation. Organizations should also implement robust input validation and sanitization measures to prevent malformed HTML from reaching the parsing layer. The recommended approach includes using dedicated HTML sanitization libraries such as github.com/microcosm-cc/bluemonday or similar tools that can filter out dangerous HTML patterns before they reach the core parser. Additionally, applications should implement proper error handling and panic recovery mechanisms to prevent crash propagation, though this does not address the underlying issue. Security practitioners should monitor for this vulnerability in their Go applications and ensure that all dependencies are updated to versions that contain the fix. This vulnerability aligns with CWE-129, which describes improper validation of array index bounds, and could be mapped to ATT&CK technique T1203, representing exploitation of software vulnerabilities for denial of service attacks. Organizations should also consider implementing web application firewalls and input filtering mechanisms to protect against exploitation attempts targeting this specific parsing flaw.