# CVE-2026-6554: libpcap BPF interpreter infinite loop in ja instruction

Source: https://junglewise.ai/threats/cve-2026-6554-libpcap-bpf-interpreter-infinite-loop-in-ja-instruction  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-09-05. Updated: 2026-09-26  
License: CC BY 4.0 with a link back

CVE-2026-6554 · Severity: medium · CVSS 5.5 · Published 2026-09-05

libpcap is a widely-used packet capture library that filters network traffic based on compiled filter rules. A flaw in the BPF interpreter allows a specially crafted filter program to cause an infinite loop, potentially freezing packet processing and causing denial of service. This vulnerability only affects uncommon use cases where external filter programs bypass libpcap's normal validation.

Technologies: [Tcpdump.Org Libpcap](https://junglewise.ai/threats/technologies/libpcap). Vendors: [Tcpdump.Org](https://junglewise.ai/threats/vendors/tcpdump-org).

## Quick answers

**Is CVE-2026-6554 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-6554 being exploited in the wild.

**How severe is CVE-2026-6554?** Medium severity, with a CVSS score of 5.5, published 5 September 2026.

**Which products and versions are affected?** tcpdump.org libpcap.

**Is there a fix for CVE-2026-6554?** A patch was published on 2026-09-05: Fix committed (ff3c834) limiting backward jumps and validating filter programs Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-6554 attacked?** It is attacked with local access, in a software library.

**Am I affected by CVE-2026-6554?** Check whether you run Tcpdump.Org Libpcap. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

The vulnerability exists in the pcapint_filter_with_aux_data() function, which interprets BPF bytecode. The "ja L" (unconditional jump) instruction's offset is treated as a signed integer, allowing backward jumps; however, the interpreter does not limit the number of loop iterations. A crafted external filter program can cause an infinite backward jump loop. The fix enforces a hard-coded limit on the number of backward jumps per packet and adds detection for immediately obvious infinite-loop patterns in pcapint_validate_filter(). This affects only programs from external sources via pcap_offline_filter() or the deprecated bpf_filter() function, not programs generated by libpcap's own compiler.

## Affected products

- tcpdump.org libpcap

## Timeline

- 2026-09-05: disclosed
- 2026-09-05: patched: Fix committed (ff3c834) limiting backward jumps and validating filter programs

## References

- [https://github.com/the-tcpdump-group/libpcap/commit/ff3c83475ac303c6b681c52ad0b6e14795a8e0ce](https://github.com/the-tcpdump-group/libpcap/commit/ff3c83475ac303c6b681c52ad0b6e14795a8e0ce)

## Related threats

- [libpcap BPF interpreter buffer bounds check bypass](https://junglewise.ai/threats/cve-2026-31912-libpcap-bpf-interpreter-buffer-bounds-check-bypass)
- [libpcap BPF interpreter abort on invalid opcode](https://junglewise.ai/threats/cve-2026-31911-libpcap-bpf-interpreter-abort-on-invalid-opcode)
- [libpcap RPCAP message validation buffer over-read](https://junglewise.ai/threats/cve-2026-18238-libpcap-rpcap-message-validation-buffer-over-read)
- [libpcap BPF interpreter scratch memory validation bypass](https://junglewise.ai/threats/cve-2026-0799-libpcap-bpf-interpreter-scratch-memory-validation-bypass)