CVE-2020-36306 in Redmine
Summary
by MITRE • 04/06/2021
Redmine before 4.0.7 and 4.1.x before 4.1.1 has XSS via the back_url field.
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Analysis
by VulDB Data Team • 04/10/2021
The vulnerability identified as CVE-2020-36306 represents a cross-site scripting weakness in the Redmine project management platform that affects versions prior to 4.0.7 and 4.1.1. This vulnerability specifically targets the back_url field parameter, which is commonly used in web applications to redirect users back to their previous location after completing an action. The flaw allows attackers to inject malicious scripts that execute in the context of other users' browsers when they navigate to pages containing the vulnerable parameter.
The technical implementation of this vulnerability stems from insufficient input validation and output encoding within Redmine's handling of the back_url parameter. When users are redirected to pages that utilize this parameter, the application fails to properly sanitize or encode user-supplied input before rendering it in the browser context. This creates an environment where malicious actors can craft URLs containing script payloads that will execute when other users click on links or navigate through the application. The vulnerability operates under CWE-79 which specifically addresses cross-site scripting flaws in web applications.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, credential theft, data exfiltration, and privilege escalation within the Redmine environment. An attacker who successfully exploits this vulnerability could potentially impersonate legitimate users, access confidential project information, modify data, or even gain administrative privileges depending on the target user's permissions. The attack vector is particularly concerning because it leverages legitimate redirection mechanisms that users typically trust, making social engineering attacks more effective.
Organizations using affected Redmine versions face significant security risks as this vulnerability can be exploited through various attack vectors including phishing emails, compromised websites, or malicious links shared within the application. The vulnerability's impact is amplified by the fact that Redmine is widely used in enterprise environments for project management and issue tracking, making it an attractive target for threat actors. Users with administrative privileges represent particularly high-value targets since successful exploitation could lead to complete system compromise. The vulnerability also aligns with ATT&CK technique T1566 which covers spearphishing with a malicious attachment or link, as attackers can craft malicious URLs that appear legitimate to end users.
The recommended mitigation strategy involves immediate deployment of the patched versions of Redmine, specifically upgrading to version 4.0.7 or 4.1.1 and later. Organizations should also implement additional defensive measures including input validation at multiple layers, output encoding of all user-supplied data, and regular security scanning of web applications. Network-based solutions such as web application firewalls can provide additional protection, though they should not be considered a complete substitute for proper code-level fixes. Security teams should also conduct thorough vulnerability assessments to identify any potential exploitation attempts and implement monitoring for suspicious user activities. The fix implemented by Redmine developers typically involves proper sanitization of the back_url parameter and ensuring that all user input is properly escaped before being rendered in HTML contexts.