CVE-2021-40541 in PHPFusion
Summary
by MITRE • 10/11/2021
PHPFusion 9.03.110 is affected by cross-site scripting (XSS) in the preg patterns filter html tag without "//" in descript() function An authenticated user can trigger XSS by appending "//" in the end of text.
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Analysis
by VulDB Data Team • 10/14/2021
The vulnerability identified as CVE-2021-40541 affects PHPFusion version 9.03.110 and represents a cross-site scripting flaw that exploits improper input sanitization within the descript() function. This issue specifically manifests when processing preg patterns filter html tags, where the application fails to adequately sanitize user input containing the forward slash characters. The vulnerability requires an authenticated user context to exploit, meaning that an attacker must first gain valid credentials to the system before being able to execute the malicious payload. The flaw occurs in the descript() function which processes text input and attempts to filter html tags while simultaneously handling preg pattern matching operations.
The technical implementation of this vulnerability stems from insufficient validation and sanitization of user-supplied data within the application's text processing pipeline. When an authenticated user submits content containing html tags with preg patterns, the system does not properly escape or filter the forward slash characters that appear in the descript() function's processing logic. The specific condition that triggers the vulnerability occurs when a user appends "//" to the end of their text input, which causes the application to improperly handle the html tag filtering mechanism. This results in malicious javascript code being injected into the application's output, which then executes in the context of other users' browsers when they view the affected content.
The operational impact of this vulnerability extends beyond simple script execution, as it can enable attackers to perform various malicious activities including session hijacking, data theft, and privilege escalation within the application. Since the vulnerability requires authentication, attackers must first compromise user credentials through phishing, credential stuffing, or other social engineering techniques to exploit this flaw. The vulnerability affects all users who view content created by the authenticated attacker, potentially compromising the entire user base of the application. The XSS payload can be designed to steal cookies, redirect users to malicious sites, or perform actions on behalf of authenticated users, making this a significant security risk for any organization relying on PHPFusion for content management.
Mitigation strategies for CVE-2021-40541 should include immediate patching of the affected PHPFusion version to the latest stable release that contains the fix for this vulnerability. Organizations should also implement comprehensive input validation and sanitization measures that properly escape all html characters and special regex patterns before processing user content. The implementation of Content Security Policy headers can provide additional defense-in-depth protection against XSS attacks by restricting the sources from which scripts can be executed. Regular security audits and code reviews should be conducted to identify similar input handling vulnerabilities in other parts of the application. The vulnerability aligns with CWE-79 which specifically addresses cross-site scripting flaws in web applications, and follows the ATT&CK technique T1059.007 for script injection. Organizations should also consider implementing web application firewalls and monitoring for suspicious input patterns that may indicate attempts to exploit this or similar vulnerabilities.