CVE-2010-1156 in Irssi
Summary
by MITRE
core/nicklist.c in Irssi before 0.8.15 allows remote attackers to cause a denial of service (NULL pointer dereference and application crash) via vectors related to an attempted fuzzy nick match at the instant that a victim leaves a channel.
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Analysis
by VulDB Data Team • 01/26/2025
The vulnerability identified as CVE-2010-1156 represents a critical denial of service flaw within the Irssi IRC client software. This issue affects versions prior to 0.8.15 and stems from improper handling of nickname matching operations during channel leave events. The vulnerability specifically manifests in the core/nicklist.c module where the software fails to properly validate pointer references during fuzzy nickname matching procedures. When a remote attacker crafts a malicious IRC message that triggers a fuzzy nick match attempt while a user is in the process of leaving a channel, the application encounters a NULL pointer dereference condition that inevitably leads to application crash and subsequent denial of service.
The technical implementation of this vulnerability leverages the timing aspect of IRC protocol operations to exploit a race condition within the nicklist handling subsystem. During normal IRC operations, when users join or leave channels, the client maintains a dynamic list of nicknames associated with each channel. The fuzzy matching functionality attempts to find similar nicknames when exact matches cannot be found, which typically occurs when users change their nicknames or when the client receives malformed data. The flaw occurs when the system attempts to process a fuzzy match operation while simultaneously processing a channel departure event, creating a scenario where a pointer that should contain valid nickname data becomes NULL, resulting in immediate application termination upon dereference.
This vulnerability directly maps to CWE-476 which describes NULL Pointer Dereference, a common software flaw that occurs when an application attempts to access a memory location through a pointer that has not been properly initialized or has been set to NULL. The operational impact of this vulnerability extends beyond simple service disruption as it can be exploited by remote attackers without requiring authentication or privileged access. The attacker merely needs to connect to a channel where the targeted user is present and send a specially crafted message that triggers the specific sequence of events leading to the crash. This makes the vulnerability particularly dangerous in environments where Irssi clients are used for critical communications or where automated monitoring systems depend on continuous client availability.
The attack pattern associated with CVE-2010-1156 follows established methodologies described in the MITRE ATT&CK framework under the T1499 category for Network Denial of Service, where adversaries leverage application-level flaws to disrupt service availability. The vulnerability demonstrates how seemingly innocuous IRC protocol features can become attack vectors when not properly validated against concurrent operations. Organizations relying on Irssi for IRC communications face significant risk as this flaw can be exploited by anyone with network access to the affected server, making it particularly concerning for public IRC networks or services where untrusted users can connect.
Mitigation strategies for this vulnerability center around immediate software updates to version 0.8.15 or later, which contain the necessary patches to properly handle the race condition between nickname matching and channel leave operations. System administrators should also implement network-level controls to monitor for unusual IRC traffic patterns that might indicate exploitation attempts. Additional defensive measures include configuring network firewalls to limit IRC client connections from untrusted sources and implementing intrusion detection systems that can identify and alert on malformed IRC messages targeting this specific vulnerability pattern. The fix implemented in the patched versions ensures that proper null checks are performed before dereferencing pointers during nickname matching operations, thereby preventing the application crash that occurred in vulnerable versions.