CVE-2017-5194 in irssi
Summary
by MITRE
Use-after-free vulnerability in Irssi before 0.8.21 allows remote attackers to cause a denial of service (crash) via an invalid nick message.
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Analysis
by VulDB Data Team • 09/03/2020
The CVE-2017-5194 vulnerability represents a critical use-after-free flaw discovered in Irssi version 0.8.20 and earlier, affecting the widely-used text-based internet relay chat client. This vulnerability resides within the client's handling of network messages, specifically when processing invalid nick messages from remote servers or clients. The flaw enables remote attackers to trigger a denial of service condition that causes the application to crash and terminate unexpectedly. Irssi, being a fundamental tool for IRC communication in both personal and enterprise environments, makes this vulnerability particularly concerning as it can disrupt ongoing chat sessions and potentially impact collaborative workflows. The vulnerability affects systems where Irssi is deployed as a client application, particularly in scenarios where users connect to public or untrusted IRC networks where malicious actors could exploit this weakness.
The technical implementation of this vulnerability stems from improper memory management within Irssi's message processing subsystem. When the client receives an invalid nick message, the application fails to properly validate the message structure before attempting to free memory resources that may have already been deallocated. This use-after-free condition occurs in the context of the client's network protocol handling, specifically in how it processes user nicknames and associated metadata. The flaw is classified under CWE-416, which describes the use of freed memory vulnerability pattern, where a program continues to reference memory that has already been freed. The memory corruption resulting from this flaw typically manifests as a segmentation fault or access violation during the message processing lifecycle, leading to the application's abrupt termination. The vulnerability is particularly insidious because it requires minimal input from attackers to exploit, making it a preferred vector for denial of service attacks against IRC clients.
The operational impact of CVE-2017-5194 extends beyond simple service disruption, as it can compromise the availability of critical communication channels within organizations. In enterprise environments where Irssi serves as a primary communication tool for system administrators, developers, or support teams, this vulnerability can lead to significant productivity losses and potential security implications. The remote exploitation capability means that attackers do not need physical access to target systems, allowing them to disrupt services from anywhere on the internet. The vulnerability affects both standalone client installations and network configurations where Irssi is used as part of larger communication infrastructures. Organizations that rely on IRC-based monitoring or alerting systems may experience cascading failures when the client crashes, potentially leading to missed critical alerts or system notifications. The impact is further amplified in environments where multiple users connect to the same IRC network, as a successful exploitation could affect numerous clients simultaneously.
Mitigation strategies for CVE-2017-5194 focus primarily on updating to the patched version of Irssi, specifically version 0.8.21 or later, which contains the necessary memory management fixes. System administrators should prioritize patching all affected installations, particularly those exposed to untrusted networks or public internet access. Network segmentation and access controls can provide additional defense-in-depth measures by limiting exposure to potentially malicious IRC traffic. Implementing proper input validation at the network level and monitoring for unusual nick message patterns can help detect potential exploitation attempts. Security teams should consider deploying intrusion detection systems that can identify malformed IRC messages indicative of exploitation attempts. The vulnerability also highlights the importance of maintaining up-to-date software across all networked systems, as Irssi's client-side nature makes it susceptible to attacks from various network positions. Organizations should also implement regular security assessments and vulnerability scanning to identify other potential use-after-free conditions within their IRC client deployments and related communication tools. This vulnerability serves as a reminder of the critical need for proper memory management practices in network applications and the potential consequences of inadequate input validation in protocol handling code.