Description

libpcap BPF interpreter calls abort() if it encounters a BPF instruction that has an invalid opcode. In particular uncommon use cases a crafted filter program can terminate the OS process.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "5.5",
  "pubDate": "2026-09-05T19:16:55.707Z",
  "pubdate": "2026-09-05T19:16:55.707Z",
  "executiveSummary": "The libpcap BPF interpreter exhibits a critical vulnerability where it invokes the abort() system call upon encountering an invalid BPF (Berkeley Packet Filter) opcode.\nThis vulnerability is categorized as a Denial of Service (DoS) flaw.\nThe issue affects any application utilizing libpcap to process BPF filters, potentially leading to the abrupt termination of the host process if a crafted, malicious filter program is supplied.\nThe impact is significant for security monitoring tools, network analyzers, and packet capturing software, as a successful exploit causes an immediate process crash, thereby disrupting service availability.\nThe attack vector involves the injection or supply of a malformed BPF filter. If an attacker can influence the filter compilation or loading process, they can force the application to terminate.\nThe requirement for exploitation is the ability to provide a crafted BPF instruction stream to the vulnerable interpreter component. This vulnerability does not require authentication to the underlying system, but rather relies on the application's interface for accepting and processing filter programs.",
  "technicalDetails": "The root cause of this vulnerability lies in the improper handling of undefined or invalid opcodes within the libpcap BPF interpreter implementation. When the interpreter logic encounters a bytecode instruction that does not conform to the expected BPF opcode definitions, it triggers a fatal runtime error by calling abort().\nThe BPF interpreter is a core component within libpcap responsible for executing packet filters in kernel or user space. BPF bytecode consists of a sequence of instructions, where each instruction is defined by an opcode, a jump offset, and a constant value. The interpreter performs a switch-case or similar dispatch mechanism to handle these opcodes.\nIn the vulnerable implementation, the default case or an explicit validation check is missing, leading to an unhandled state when an unexpected instruction is encountered. Instead of returning an error code or gracefully rejecting the filter, the library calls abort(), which sends a SIGABRT signal to the host process, causing an immediate crash.\nThe attack flow follows a structured path: first, the attacker generates a malicious BPF program containing an unsupported or out-of-range opcode. Second, this payload is passed to the application via an interface that accepts user-defined filters, such as an input field in a network configuration utility or an API endpoint that compiles and installs BPF filters. Third, the libpcap library processes the filter bytecode through the interpreter. Finally, upon encountering the malicious opcode, the interpreter executes the abort() instruction, terminating the parent process.\nThis behavior represents a failure in robust input validation and error handling within the BPF execution engine. Because libpcap is often used in privileged network-facing applications, a crash induced by an attacker can cause a denial of service on mission-critical monitoring infrastructure. There are no privilege requirements beyond the ability to influence the filter input. The exposure depends entirely on the application's attack surface; however, any application allowing untrusted users to define packet filters is susceptible. Post-exploitation impact is limited to the termination of the service, which may cause system instability or bypass security monitoring controls depending on the deployment environment."
}