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.

CVE-2026-0799 affects the libpcap BPF interpreter, which fails to validate the register index used in BPF instructions that load or store values from scratch memory registers. The register index is an unsigned 32-bit integer and must not exceed 15, but this constraint is not enforced. A crafted BPF filter program can exploit this flaw to cause the interpreter to read and write arbitrary OS process memory. On 64-bit architectures, the affected memory range spans 16GiB starting from the current stack frame. On 32-bit architectures, the entire address space is potentially accessible. This vulnerability can be triggered in uncommon but valid use cases, making it a significant memory safety issue. The issue has been addressed in a commit to the official libpcap repository on GitHub.