CVE-2017-15721 in irssi
Summary
by MITRE
In Irssi before 1.0.5, certain incorrectly formatted DCC CTCP messages could cause a NULL pointer dereference. This is a separate, but similar, issue relative to CVE-2017-9468.
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Analysis
by VulDB Data Team • 01/04/2023
The vulnerability identified as CVE-2017-15721 represents a critical null pointer dereference flaw within the Irssi IRC client software affecting versions prior to 1.0.5. This vulnerability specifically manifests when the application processes certain malformed DCC CTCP messages, which are used for direct client-to-client communication within IRC networks. The issue stems from inadequate input validation mechanisms that fail to properly handle malformed message structures, leading to a crash condition when the software attempts to dereference a null pointer during message processing. This type of vulnerability falls under the CWE-476 category of NULL Pointer Dereference, which is classified as a fundamental memory safety issue that can lead to application instability and potential denial of service conditions. The vulnerability is particularly concerning because it affects a widely used IRC client that many users rely on for communication and collaboration purposes.
The technical exploitation of this vulnerability occurs when an attacker sends a specially crafted DCC CTCP message that contains malformed data structures or unexpected field values. When Irssi processes this malformed message, the application's parsing logic fails to properly validate the message format, resulting in a scenario where a pointer variable that should contain a valid memory address instead holds a null value. Upon subsequent processing attempts, the software tries to dereference this null pointer, causing an immediate application crash or segmentation fault. This behavior is consistent with the ATT&CK technique T1499.004 which involves network denial of service attacks through malformed input handling. The vulnerability demonstrates poor error handling practices in the software's message parsing subsystem, where proper boundary checks and input sanitization mechanisms are either missing or insufficient to prevent the null pointer dereference condition.
The operational impact of CVE-2017-15721 extends beyond simple application crashes to potentially disrupt communication services for users relying on Irssi for IRC connectivity. In practical scenarios, this vulnerability could be exploited by malicious actors to perform denial of service attacks against individual users or entire IRC networks, effectively preventing legitimate users from participating in chat sessions or file transfers. The vulnerability's similarity to CVE-2017-9468 indicates a pattern of issues within the same software component, suggesting that the DCC CTCP message handling subsystem contains multiple related weaknesses that require comprehensive remediation. Organizations and users who depend on Irssi for critical communication infrastructure face potential operational disruptions, as the application becomes unstable under adversarial input conditions and may require frequent restarts or complete system reinstallation to restore functionality.
Mitigation strategies for CVE-2017-15721 should prioritize immediate software updates to Irssi version 1.0.5 or later, which contains the necessary patches to address the null pointer dereference vulnerability. System administrators should implement network monitoring to detect and block suspicious DCC CTCP messages that may contain malformed structures, although this approach provides only partial protection. The vulnerability highlights the importance of robust input validation and error handling in client applications that process untrusted network data, aligning with security best practices outlined in the OWASP Top Ten. Additionally, users should disable DCC functionality when not required, as this reduces the attack surface and limits potential exploitation vectors. The remediation process should also include comprehensive testing of updated software versions to ensure that the vulnerability has been properly addressed and that no regressions have been introduced in the application's core functionality.