CVE-2017-5193 in irssi
Summary
by MITRE
The nickcmp function in Irssi before 0.8.21 allows remote attackers to cause a denial of service (NULL pointer dereference and crash) via a message without a nick.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2017-5193 affects Irssi, a popular console-based IRC client, specifically versions prior to 0.8.21. This issue resides in the nickcmp function which is responsible for comparing nicknames within IRC communications. The flaw represents a classic null pointer dereference vulnerability that can be exploited by remote attackers to disrupt service availability. The vulnerability occurs when the IRC client processes messages that lack proper nickname information, creating a scenario where the application attempts to dereference a null pointer during comparison operations.
The technical implementation of this vulnerability stems from inadequate input validation within the nickcmp function. When Irssi receives an IRC message that does not contain a valid nickname field, the function fails to properly handle this edge case and proceeds to attempt operations on a null pointer reference. This type of flaw falls under CWE-476 which specifically addresses NULL pointer dereference conditions in software implementations. The absence of proper null checks before pointer operations creates an exploitable condition that can be triggered through crafted IRC messages.
From an operational perspective, this vulnerability enables remote attackers to execute a denial of service attack against Irssi instances without requiring any authentication or special privileges. The attack vector is particularly concerning because it can be executed over the network using standard IRC protocols, making it accessible to anyone who can establish a connection to the target system. When successfully exploited, the vulnerability results in immediate application crashes and service disruption, effectively rendering the IRC client unusable until manual restart occurs. This makes the vulnerability particularly dangerous in environments where continuous connectivity is required or where automated monitoring systems depend on Irssi for communication.
The impact of this vulnerability extends beyond simple service disruption as it demonstrates a fundamental flaw in input handling and error management within the IRC client. Attackers can leverage this weakness to repeatedly crash services, potentially causing persistent availability issues for users who rely on Irssi for critical communications. The vulnerability also highlights the importance of proper defensive programming practices including null pointer validation and robust error handling mechanisms. Organizations using Irssi should prioritize immediate patching to version 0.8.21 or later, as this update includes the necessary fixes to prevent the null pointer dereference condition. Additionally, network administrators should consider implementing monitoring solutions to detect unusual crash patterns that might indicate exploitation attempts. The ATT&CK framework categorizes this vulnerability under privilege escalation and denial of service tactics, as it allows attackers to disrupt services without requiring elevated privileges, making it a particularly effective vector for service disruption attacks.