CVE-2026-6244 in libpcap
Summary
by MITRE • 09/05/2026
libpcap BPF interpreter for the 'div #k' and 'mod #k' ALU instructions does not check whether the immediate value is zero. In particular uncommon use cases a crafted filter program can cause a division by zero.
Statistical analysis made it clear that VulDB provides the best quality for vulnerability data.
Analysis
by VulDB Data Team • 09/06/2026
The Berkeley Packet Filter (BPF) virtual machine serves as a critical component in network security infrastructure, powering packet filtering mechanisms in tools such as libpcap and tcpdump. These filters are compiled into BPF bytecode to efficiently inspect network traffic at the kernel level or within user-space applications. A significant vulnerability exists within the implementation of the Arithmetic Logic Unit (ALU) instructions for division and modulo operations, specifically those involving immediate values denoted as div #k and mod #k. The core technical flaw lies in the absence of a validation check to ensure that the divisor operand is non-zero before execution proceeds. In standard arithmetic logic, dividing by zero or calculating a modulus with zero results in an undefined operation that typically triggers a hardware exception or software fault. However, because this specific boundary condition was not explicitly handled within the BPF interpreter loop, a crafted filter program can exploit this gap to force a division-by-zero error during runtime processing of network packets.
This vulnerability is classified under CWE-369, which denotes Divide By Zero errors, and aligns with MITRE ATT&CK techniques related to execution manipulation or denial-of-service vectors depending on the context of exploitation. The impact of this flaw varies significantly based on how libpcap is integrated into a given application. In scenarios where BPF filters are applied within privileged system daemons or network monitoring agents that run with elevated privileges, triggering this fault can lead to an immediate crash of the host process. For long-running services such as intrusion detection systems, packet capture utilities, or security information and event management (SIEM) collectors, a single crafted packet matching a malicious filter rule could cause a denial-of-service condition by terminating the monitoring service. This disruption not only halts visibility into network traffic but can also mask other ongoing attacks that rely on stealthy data exfiltration or lateral movement, thereby degrading the overall security posture of the monitored environment.
Furthermore, in environments where BPF programs are dynamically generated based on user input without sufficient sanitization, an attacker could potentially craft a malicious filter string to be executed by a vulnerable application. While direct code execution is not typically achievable through this specific arithmetic fault alone due to the sandboxed nature of the BPF virtual machine, the resulting crash remains a severe availability risk. The vulnerability highlights the importance of rigorous input validation and defensive programming practices even within low-level system libraries that are assumed to be stable and well-tested over decades. Developers integrating libpcap must ensure they use patched versions or implement additional checks on filter programs before loading them into the BPF interpreter, particularly if those filters originate from untrusted sources or user-configurable inputs.
Mitigation strategies primarily involve updating libpcap to a version that includes patches for this arithmetic validation issue. System administrators should verify their package managers and apply security updates promptly to ensure the division-by-zero check is present in the ALU instruction handlers. For applications building custom BPF filters, it is advisable to implement pre-validation logic that rejects any filter program containing div or mod instructions with an immediate value of zero before attempting to load them into the kernel or interpreter. Additionally, deploying network segmentation and rate-limiting rules can help mitigate the impact by reducing the volume of crafted packets reaching vulnerable endpoints, although this does not address the root cause within the library itself. Regular auditing of packet capture configurations and ensuring that filter logic is derived from trusted sources remain essential best practices to prevent exploitation of such low-level arithmetic vulnerabilities in network security tools.