CVE-2016-9471 in Adserver
Summary
by MITRE
Revive Adserver before 3.2.5 and 4.0.0 suffers from Special Element Injection. Usernames weren't properly sanitised when creating users on a Revive Adserver instance. Especially, control characters were not filtered, allowing apparently identical usernames to co-exist in the system, due to the fact that such characters are normally ignored when an HTML page is displayed in a browser. The issue could have therefore been exploited for user spoofing, although elevated privileges are required to create users within Revive Adserver.
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Analysis
by VulDB Data Team • 11/22/2022
The CVE-2016-9471 vulnerability represents a critical security flaw in Revive Adserver versions prior to 3.2.5 and 4.0.0, specifically targeting the application's user account creation mechanism. This vulnerability falls under the category of Special Element Injection, a technique that exploits the way applications handle special characters during user input processing. The flaw stems from inadequate sanitization of usernames during user creation, where control characters were not properly filtered or removed from the input validation process. This oversight creates a fundamental weakness in the application's authentication and authorization framework, as it allows for the creation of multiple user accounts with seemingly identical usernames that differ only in the presence of invisible control characters.
The technical implementation of this vulnerability exploits the inherent behavior of web browsers and HTML rendering engines, where certain control characters are silently ignored or rendered invisibly during display operations. This means that two users could theoretically be created with usernames that appear identical when displayed in the browser interface, yet are technically distinct due to the presence of control characters in one or both usernames. The vulnerability specifically targets the HTML rendering layer where such characters are normalized or stripped out, creating a discrepancy between how the system internally stores user credentials and how they are presented to users. This fundamental mismatch creates opportunities for attackers to manipulate user identification and potentially exploit the system's user management functions through subtle character manipulation.
The operational impact of this vulnerability extends beyond simple user spoofing, as it fundamentally undermines the integrity of the user authentication system within Revive Adserver. While the vulnerability requires elevated privileges to create new users, the ability to create multiple accounts with identical-looking usernames creates confusion and potential security risks in user management operations. Attackers could potentially exploit this to impersonate legitimate users, manipulate access controls, or create confusion within the system's user directory. The vulnerability's impact is particularly concerning because it operates at the core of user identification and authentication, making it a potential vector for more serious attacks including privilege escalation or unauthorized access to sensitive advertising data and system resources.
This vulnerability aligns with CWE-77 and CWE-78, which address improper neutralization of special elements used in SQL commands and shell commands respectively, although the specific implementation here deals with HTML rendering and user interface presentation rather than command injection. The attack pattern follows elements of the ATT&CK framework's privilege escalation and credential access techniques, where attackers leverage system weaknesses to gain unauthorized access or manipulate user identities. The vulnerability demonstrates how seemingly minor input validation issues can create significant security implications when combined with the way web browsers handle character encoding and display normalization. Organizations should implement comprehensive input sanitization measures, including thorough character filtering and validation, to prevent similar vulnerabilities in user management systems. The fix involves proper implementation of username validation that removes or escapes control characters before account creation, ensuring that user identifiers are both unique and properly normalized for display purposes.