BPF Looping Vulnerability in libpcap

Executive Summary

This vulnerability involves libpcap's BPF interpreter incorrectly handling 'ja L' instructions in filter programs. The interpreter treats the offset as a signed integer to allow backward jumps for looping but lacks a limit on loop iterations. This can lead to infinite loops if a crafted filter program uses backward jumps excessively, causing a denial-of-service condition.

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Detection Guidance

Detecting this vulnerability requires checking if your libpcap version is affected. Use the command 'tcpdump --version' to check the installed version. If your version is below the patched release, the system is vulnerable. Additionally, monitor for unusual CPU usage spikes during packet capture operations, which may indicate an infinite loop caused by malicious BPF programs.

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Impact Analysis

The vulnerability could cause system hangs or crashes if a malicious or malformed BPF filter program is processed by libpcap. This may lead to denial-of-service, disrupting network monitoring or packet capture operations on affected systems.

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Mitigation Strategies

Immediately update libpcap to the latest patched version. If updating is not possible, restrict the use of externally sourced BPF programs and avoid using deprecated functions like pcap_offline_filter() or bpf_filter(). Implement network monitoring to detect abnormal CPU usage during packet capture operations.

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