CVE-2017-6909 in Shimmie
Summary
by MITRE
An issue was discovered in Shimmie <= 2.5.1. The vulnerability exists due to insufficient filtration of user-supplied data (log) passed to the "shimmie2-master/ext/chatbox/history/index.php" URL. An attacker could execute arbitrary HTML and script code in a browser in the context of the vulnerable website.
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Analysis
by VulDB Data Team • 12/29/2019
The vulnerability identified as CVE-2017-6909 represents a critical cross-site scripting flaw in the Shimmie image board software version 2.5.1 and earlier. This issue stems from inadequate input validation mechanisms within the chatbox history component, specifically in the file path ext/chatbox/history/index.php. The flaw allows malicious actors to inject arbitrary HTML and script code through user-supplied log data, creating a persistent XSS attack vector that can compromise user sessions and execute unauthorized commands within the browser context of the vulnerable website. The vulnerability specifically affects the chatbox functionality where user-generated content is displayed without proper sanitization of potentially malicious input.
The technical exploitation of this vulnerability occurs through the manipulation of log data that gets processed and rendered in the chatbox history display. When users submit messages or log entries through the chat functionality, the application fails to adequately filter or escape special characters that could be interpreted as HTML or JavaScript code. This insufficient filtration creates an environment where attackers can embed malicious scripts within the log entries, which then get executed when other users view the chat history. The vulnerability manifests as a reflected XSS attack since the malicious code is stored and then reflected back to users who access the affected page. This flaw directly maps to CWE-79 which defines Cross-Site Scripting as the improper handling of input data that can be interpreted as executable code by web browsers.
The operational impact of this vulnerability extends beyond simple script execution, potentially enabling attackers to perform session hijacking, deface the website, steal user credentials, or redirect victims to malicious sites. An attacker could craft a log entry containing malicious JavaScript that would execute in the context of other users' browsers, allowing for the capture of cookies, session tokens, or other sensitive information. The persistent nature of stored XSS attacks means that the malicious code remains active until the affected page is refreshed or the log entries are manually removed. This vulnerability particularly impacts web applications that rely on user-generated content for chat functionality or logging mechanisms, making it a significant concern for community-driven platforms and forums.
Security mitigations for CVE-2017-6909 should focus on implementing comprehensive input validation and output encoding mechanisms. The most effective approach involves sanitizing all user-supplied data before rendering it in the browser context, specifically through the implementation of proper HTML entity encoding for characters such as <, >, &, ", and '. Additionally, developers should implement Content Security Policy headers to limit the execution of inline scripts and restrict the sources from which scripts can be loaded. The vulnerability also highlights the importance of following secure coding practices outlined in the OWASP Top Ten and MITRE ATT&CK framework, particularly in the areas of input validation and output encoding. Organizations should also consider implementing regular security updates and vulnerability scanning to identify similar issues in other components of their web applications. The remediation process should include thorough code review of all user input handling mechanisms and the implementation of automated testing procedures to validate that input data is properly sanitized before being processed or displayed in web interfaces.