CVE-2017-5195 in irssi
Summary
by MITRE
Irssi 0.8.17 before 0.8.21 allows remote attackers to cause a denial of service (out-of-bounds read and crash) via a crafted ANSI x8 color code.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2017-5195 affects Irssi version 0.8.17 through 0.8.20, representing a critical remote denial of service flaw that stems from improper handling of ANSI color codes. This issue manifests when the vulnerable application processes specially crafted ANSI x8 color codes, leading to out-of-bounds memory reads that ultimately result in application crashes. The flaw resides in the terminal color handling mechanism within Irssi's text processing pipeline, where insufficient input validation allows maliciously formatted color codes to trigger memory access violations.
This vulnerability operates through a classic buffer over-read condition that falls under the Common Weakness Enumeration category of CWE-125, specifically involving out-of-bounds read access. The attack vector requires remote exploitation through network communication channels where Irssi receives and processes text data containing the malicious ANSI color codes. The flaw demonstrates characteristics consistent with the ATT&CK technique T1499.004, which involves network denial of service attacks targeting application stability. When an attacker sends a crafted message containing the specially formatted ANSI x8 color code, the application's parser fails to properly validate the color code boundaries, causing the program to attempt accessing memory locations beyond the allocated buffer space.
The operational impact of this vulnerability extends beyond simple application instability, as it can be leveraged to create persistent denial of service conditions within chat environments where Irssi is deployed. Attackers can exploit this weakness to repeatedly crash chat clients, disrupting communication channels and potentially affecting larger network operations. The vulnerability affects both server and client implementations of Irssi, making it particularly dangerous in multi-user environments where chat servers may be targeted to disrupt services for all connected users. The out-of-bounds read condition creates a predictable crash pattern that can be reliably exploited to maintain persistent service disruption.
Mitigation strategies for CVE-2017-5195 primarily involve upgrading to Irssi version 0.8.21 or later, which includes proper input validation and bounds checking for ANSI color codes. System administrators should implement network-level filtering to restrict potentially malicious text content, particularly in public chat environments where users cannot be trusted to provide legitimate input. Additionally, deploying application-level sandboxing mechanisms can help contain the impact of such vulnerabilities by isolating vulnerable components from critical system resources. Organizations should also consider implementing intrusion detection systems capable of identifying patterns associated with malicious ANSI color code sequences, providing early warning capabilities for potential exploitation attempts. The fix implemented in version 0.8.21 demonstrates proper input sanitization techniques that validate color code parameters before processing, preventing the out-of-bounds memory access that previously caused crashes.