CVE-2009-0759 in ZNC
Summary
by MITRE
Multiple CRLF injection vulnerabilities in webadmin in ZNC before 0.066 allow remote authenticated users to modify the znc.conf configuration file and gain privileges via CRLF sequences in the quit message and other vectors.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 04/27/2025
The vulnerability identified as CVE-2009-0759 represents a critical security flaw in the ZNC IRC bouncer software, specifically affecting versions prior to 0.066. This issue manifests as multiple CRLF injection vulnerabilities within the webadmin module, creating a pathway for authenticated remote attackers to manipulate the system configuration. The vulnerability exploits the improper handling of user input containing carriage return line feed sequences, which are commonly used to terminate protocol connections and delimit data in network communications. The affected webadmin interface in ZNC provides administrative functions through a web-based interface, making it a prime target for exploitation by attackers who can authenticate to the system.
The technical implementation of this vulnerability stems from insufficient input validation and sanitization within the webadmin module's handling of user-provided data. When users submit data through the web interface, particularly in fields such as quit messages and other configuration parameters, the system fails to properly escape or filter CRLF characters. This allows attackers to inject malicious sequences that can manipulate HTTP headers or configuration file content. The flaw operates at the application layer, specifically targeting the configuration management functionality where user input is processed and written to the znc.conf file. According to CWE-113, this vulnerability maps directly to improper neutralization of CRLF sequences, a well-documented weakness in web applications that enables header injection attacks.
The operational impact of this vulnerability is severe and multifaceted, as it enables privilege escalation and configuration manipulation within the ZNC system. An authenticated attacker can leverage these CRLF injection vectors to modify the znc.conf file, potentially gaining elevated privileges or altering system behavior. This could result in unauthorized access to IRC channels, data exfiltration, or the ability to establish persistent backdoors within the IRC infrastructure. The vulnerability also aligns with ATT&CK technique T1059.007, which involves the use of command and scripting interpreters, as the compromised configuration could be used to execute malicious commands or establish unauthorized connections. The webadmin interface provides a convenient attack surface since it allows remote access to administrative functions, making the exploitation particularly dangerous in environments where multiple users have access to the system.
Mitigation strategies for CVE-2009-0759 should prioritize immediate software updates to ZNC version 0.066 or later, where the CRLF injection vulnerabilities have been addressed through proper input validation and sanitization. Organizations should implement comprehensive input filtering mechanisms that escape or remove CRLF sequences from all user-provided data before processing, particularly in configuration fields and user-generated content areas. Network administrators should also consider implementing additional security controls such as web application firewalls that can detect and block CRLF injection attempts. The vulnerability highlights the importance of secure coding practices and input validation, particularly in web applications that handle user data. Organizations should conduct regular security assessments of their IRC infrastructure and ensure that all components are kept up to date with the latest security patches. This vulnerability serves as a reminder of the critical need for proper input sanitization and the potential consequences of failing to address common web application weaknesses.