CVE-2016-2233 in HexChat
Summary
by MITRE
Stack-based buffer overflow in the inbound_cap_ls function in common/inbound.c in HexChat 2.10.2 allows remote IRC servers to cause a denial of service (crash) via a large number of options in a CAP LS message.
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Analysis
by VulDB Data Team • 05/13/2026
The vulnerability identified as CVE-2016-2233 represents a critical stack-based buffer overflow within the HexChat IRC client software version 2.10.2. This flaw exists in the inbound_cap_ls function located in the common/inbound.c source file, which processes CAP LS messages received from IRC servers. The vulnerability specifically manifests when remote IRC servers send CAP LS messages containing an excessive number of options, creating a condition where the application fails to properly validate input length before attempting to store data on the stack. This improper bounds checking creates an exploitable condition that can be leveraged by malicious actors to crash the application.
The technical nature of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions where insufficient bounds checking allows attackers to overwrite adjacent stack memory. The flaw operates through a classic buffer overrun scenario where the application allocates a fixed-size buffer on the stack to store CAP LS message options, but fails to verify that incoming data does not exceed this predetermined limit. When the number of options exceeds the allocated buffer space, adjacent memory locations become overwritten, potentially corrupting the stack frame and causing unpredictable behavior including application crashes or potential code execution in some scenarios.
From an operational impact perspective, this vulnerability enables remote attackers to execute denial of service attacks against HexChat users by simply connecting to a malicious IRC server and sending a specially crafted CAP LS message. The attack requires no authentication or special privileges, making it particularly dangerous as it can be executed by anyone with access to the IRC network. The crash effect prevents legitimate users from maintaining their IRC sessions, effectively disrupting their communication capabilities and potentially leading to service unavailability for those relying on the application for network connectivity. This vulnerability directly impacts the availability and reliability of the IRC client software, undermining user confidence in the application's stability.
The attack vector for CVE-2016-2233 follows patterns consistent with the ATT&CK framework's privilege escalation and denial of service tactics, specifically targeting the application layer through protocol manipulation. The vulnerability demonstrates how seemingly benign network protocol interactions can be weaponized to create system instability. Organizations using HexChat or similar IRC clients should implement immediate mitigations including updating to patched versions of the software, implementing network-level filtering to monitor and restrict unusual CAP LS message patterns, and establishing monitoring procedures to detect potential exploitation attempts. Additionally, this vulnerability underscores the importance of input validation and bounds checking in network protocol implementations, reinforcing the need for defensive programming practices and regular security assessments of client applications that process untrusted network data. The flaw serves as a reminder of how protocol handling errors in client software can create significant security risks even when the primary attack surface appears limited to denial of service conditions.