Description

In BPF instructions that load/store a value from/to a scratch memory register the register index is an unsigned 32-bit integer and must not exceed 15, but libpcap BPF interpreter does not validate the value. In particular uncommon use cases a crafted filter program can cause the interpreter to try reading and writing the OS process memory in the 16GiB starting at the current stack frame on 64-bit architectures and in the entire address space on 32-bit architectures.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "8.7",
  "pubDate": "2026-09-05T19:16:55.320Z",
  "pubdate": "2026-09-05T19:16:55.320Z",
  "executiveSummary": "The libpcap BPF interpreter contains an out-of-bounds memory access vulnerability due to insufficient validation of register indices in BPF load/store instructions.\nThe vulnerability allows an attacker to manipulate BPF filter programs to perform unauthorized read and write operations on process memory.\nOn 64-bit architectures, this vulnerability exposes a 16GiB range starting at the current stack frame, while on 32-bit architectures, it potentially exposes the entire address space.\nThis flaw can be leveraged to achieve arbitrary memory read/write primitives, potentially leading to unauthorized data disclosure, process corruption, or code execution, depending on the environment.\nSuccessful exploitation requires the victim to load and execute a specially crafted BPF filter program provided by an attacker.\nThe vulnerability represents a significant security risk to applications that process externally provided BPF filters without robust sandboxing or strict validation of the filter bytecode.",
  "technicalDetails": "The root cause of this vulnerability lies in the improper validation of register index inputs within the libpcap BPF interpreter. In the BPF specification, instructions designed to load from or store to scratch memory registers expect an unsigned 32-bit integer representing the register index. Crucially, the BPF architecture dictates that this index must not exceed 15 (representing 16 scratch memory registers).\nThe libpcap interpreter fails to enforce this constraint, allowing an attacker to supply a register index significantly larger than 15. When the interpreter executes these instructions, it uses the provided index as an offset into memory, rather than restricting it to the allocated scratch memory space.\nOn 64-bit architectures, the memory offset calculation effectively allows the interpreter to access memory within a 16GiB range relative to the current stack frame. This enables an out-of-bounds (OOB) read or write primitive by specifying an index that maps to unauthorized memory locations outside the intended BPF scratch space.\nOn 32-bit architectures, the impact is even more severe; the lack of index validation can allow the interpreter to read or write to essentially any address within the process's entire address space, as the index is not constrained by the expected memory segment boundaries.\nExploitation involves the following flow: 1. An attacker crafts a malicious BPF program containing load or store instructions with out-of-bounds register indices. 2. The attacker causes an application utilizing libpcap to load and process this malicious filter. 3. Upon execution, the libpcap interpreter processes the invalid index, treating the target memory address as a legitimate scratch register. 4. Through repeated read/write operations, the attacker can leak sensitive data from the stack or other process memory areas, or modify application-specific data, function pointers, or return addresses to gain control over the execution flow.\nThis vulnerability is inherent to the interpreter component of libpcap and is independent of specific network protocols. The ability to manipulate process memory is limited only by the permissions of the process executing the libpcap interpreter. If the process is running with elevated privileges, the impact of the exploitation is significantly amplified."
}