CVE-2018-15596 in MyBB
Summary
by MITRE
An issue was discovered in inc/class_feedgeneration.php in MyBB 1.8.17. On the forum RSS Syndication page, one can generate a URL such as http://localhost/syndication.php?fid=&type=atom1.0&limit=15. The thread titles (within title elements of the generated XML documents) aren't sanitized, leading to XSS.
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Analysis
by VulDB Data Team • 07/27/2025
The vulnerability identified as CVE-2018-15596 resides within the MyBB forum software version 1.8.17, specifically in the inc/class_feedgeneration.php file. This security flaw manifests on the forum's RSS syndication page where users can generate syndication URLs with various parameters including forum id fid type and limit. The issue stems from inadequate input sanitization of thread titles when generating XML feeds for syndication purposes. When users access the syndication page with parameters such as http://localhost/syndication.php?fid=&type=atom1.0&limit=15 the system processes thread titles without proper sanitization measures, creating a cross-site scripting vulnerability that allows malicious actors to inject arbitrary javascript code into the generated XML documents. The vulnerability operates at the application layer and affects the XML feed generation functionality specifically targeting the title elements within the atom1.0 format output. This flaw falls under the CWE-79 category of Cross-Site Scripting and represents a classic case of insufficient output sanitization where user-controllable data enters the system and is subsequently reflected back to users without proper encoding or filtering. The operational impact of this vulnerability extends beyond simple XSS attacks as it can enable attackers to execute malicious scripts in the context of affected users' browsers, potentially leading to session hijacking cookie theft or redirection to malicious sites. The vulnerability is particularly concerning because it affects the syndication functionality that many users rely on to access forum content through RSS readers and other feed consumers. Attackers can craft malicious thread titles containing javascript payloads that get embedded directly into the XML feed, making the vulnerability exploitable through standard RSS feed consumption mechanisms. The attack vector is relatively simple requiring only the creation of specially crafted thread titles that contain malicious javascript code which then gets executed when users view the feed in their browser. This vulnerability aligns with ATT&CK technique T1213 which involves data from information repositories and can be leveraged for initial access or privilege escalation. The security implications are significant as it allows attackers to compromise user sessions and potentially gain unauthorized access to forum accounts, especially in environments where users frequently consume RSS feeds from the vulnerable forum. Organizations using MyBB 1.8.17 should immediately implement mitigations including input validation and output encoding for all user-generated content that appears in syndicated feeds. The recommended solution involves sanitizing all thread titles and other user-controllable data before inclusion in XML feeds, implementing proper HTML encoding for special characters, and ensuring that feed generation processes properly escape any potentially malicious content. Additionally, patching to a newer version of MyBB that addresses this vulnerability should be prioritized to eliminate the security risk entirely. The vulnerability demonstrates the importance of proper input validation and output encoding in web applications and highlights the need for comprehensive security testing of all data processing functions, particularly those involving user-generated content and syndication features.