CVE-2020-26035 in Zammad
Summary
by MITRE • 12/28/2020
An issue was discovered in Zammad before 3.4.1. There is Stored XSS via a Tags element in a TIcket.
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Analysis
by VulDB Data Team • 12/28/2020
The vulnerability identified in Zammad versions prior to 3.4.1 represents a critical stored cross-site scripting flaw that resides within the ticket management system's tag handling functionality. This issue allows attackers to inject malicious scripts into ticket tags that persist in the database and execute whenever the affected page is loaded, creating a persistent threat vector that can compromise user sessions and data integrity. The vulnerability specifically affects the Tags element within the Ticket interface, making it one of the most dangerous attack surfaces since tags are frequently used and displayed throughout the application's user interface.
The technical implementation of this vulnerability stems from insufficient input validation and output sanitization within the tag processing pipeline. When users create or modify ticket tags, the system fails to properly escape or filter special characters that could be interpreted as HTML or JavaScript code. This inadequate sanitization allows malicious payloads to be stored in the database without proper encoding, enabling attackers to craft tags containing script tags, event handlers, or other malicious constructs that will execute in the context of other users' browsers who view the affected tickets. The flaw operates at the application layer and affects all users with appropriate permissions to modify ticket tags, making it particularly dangerous in multi-user environments where privilege escalation may not be required.
The operational impact of this stored XSS vulnerability extends beyond simple script execution and can enable sophisticated attack chains that compromise user accounts and steal sensitive information. An attacker who successfully injects malicious code into a tag can potentially steal session cookies, redirect users to phishing sites, or even perform unauthorized actions on behalf of victims through the browser's existing authentication context. This vulnerability directly relates to CWE-79 which describes cross-site scripting flaws where untrusted data is improperly handled in web applications, and aligns with ATT&CK technique T1566.002 for spearphishing attachments that could contain malicious tag content. The persistent nature of stored XSS means that the attack vector remains active until the malicious tags are removed or the system is updated, providing attackers with extended time windows to exploit the vulnerability.
Organizations utilizing Zammad versions prior to 3.4.1 should immediately implement mitigations including patching to the latest stable release which includes proper input validation and output encoding for tag elements. Administrators should also consider implementing additional security measures such as content security policy headers, regular monitoring of ticket tag modifications, and user education about the risks of clicking on untrusted tags in ticket systems. The vulnerability demonstrates the critical importance of input sanitization in web applications, particularly within user-generated content areas like tagging systems that are frequently accessed and displayed throughout application interfaces. Security teams should conduct thorough assessments of all user-facing input fields to identify similar vulnerabilities and ensure proper context-aware output encoding is implemented across the entire application stack.