CVE-2021-43695 in issabelPBX
Summary
by MITRE • 11/29/2021
An unspecified version of issabelPBX is affected by a Cross Site Scripting (XSS) vulnerability. In file page.backup_restore.php, the exit function will terminate the script and print the message to the user. The message will contain $_REQUEST without sanitization, then there is a XSS vulnerability.
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Analysis
by VulDB Data Team • 12/02/2021
The vulnerability identified as CVE-2021-43695 affects issabelPBX, a widely used open source unified communications platform that provides telephony services through a web interface. This particular flaw resides within the page.backup_restore.php file where the exit function is invoked to terminate script execution and display messages to end users. The security issue stems from improper input validation and sanitization practices that allow malicious actors to inject arbitrary script code through the $_REQUEST superglobal variable. This represents a classic cross site scripting vulnerability that can be exploited by attackers to execute malicious scripts within the context of a victim's browser session.
The technical implementation of this vulnerability demonstrates a failure in proper output encoding and input validation mechanisms. When the exit function is triggered, it directly incorporates user-supplied data from the $_REQUEST array into the displayed error message without any sanitization or encoding processes. This creates an environment where attackers can craft malicious payloads that will execute in the browser of any user who views the affected page. The vulnerability is particularly concerning as it occurs in a backup and restore functionality which may be accessed by users with administrative privileges, potentially allowing for more severe exploitation scenarios.
The operational impact of this XSS vulnerability extends beyond simple script execution as it can enable attackers to perform various malicious activities including session hijacking, credential theft, and data exfiltration from authenticated users. Attackers could potentially exploit this vulnerability to inject malicious scripts that would steal session cookies, redirect users to phishing sites, or even modify the backup and restore functionality to execute arbitrary commands on the underlying system. The attack vector is relatively simple as it requires only the manipulation of request parameters that would normally be processed by the backup restore module, making it accessible to attackers with minimal technical expertise.
From a cybersecurity perspective, this vulnerability aligns with CWE-79 which specifically addresses cross site scripting flaws in web applications. The issue also maps to ATT&CK technique T1566 which covers social engineering through malicious payloads delivered via web interfaces. Organizations using issabelPBX systems are particularly vulnerable as this flaw affects the core web interface functionality that administrators and users interact with daily. The vulnerability's impact is amplified by the fact that it occurs in a critical administrative function, potentially allowing attackers to escalate privileges or gain unauthorized access to sensitive system information. Organizations should implement immediate mitigations including input validation, output encoding, and proper parameter sanitization to prevent exploitation.
The remediation strategy for this vulnerability requires immediate patching of the affected issabelPBX version and implementation of proper input sanitization procedures throughout the application. Security teams should also consider implementing web application firewalls to detect and block malicious payloads attempting to exploit this vulnerability. Regular security audits of web applications should include thorough testing for similar input validation flaws, particularly in administrative interfaces where the potential for privilege escalation exists. Additionally, implementing content security policies and proper output encoding practices can provide additional layers of defense against similar cross site scripting vulnerabilities in the future.