# SANS Explains Multipath TCP Detection

Published: 2026-11-02 · Severity: routine
Canonical: https://vorant.io/reports/60420fb4-676a-5507-a797-da171e40e512/sans-explains-multipath-tcp-detection
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> SANS ISC explains Multipath TCP (MPTCP) mechanics and detection techniques, prompted by a new Linux kernel MPTCP vulnerability.

Source: isc.sans.edu — https://isc.sans.edu/diary/rss/33482

## What to check

- Applies to: The 1 CVE named below. Whether you run an affected version is not assessed: check the versions the source lists.
- Exploitation: No exploitation in the wild and no public exploit is recorded for the CVEs named.

This SANS Internet Storm Center diary provides background on Multipath TCP (MPTCP, RFC 8684), a TCP extension that allows connections to be split across multiple IP paths, prompted by the recent disclosure of a Linux kernel vulnerability (CVE-2026-98432) in its MPTCP implementation. Rather than detailing the vulnerability itself, the author focuses on explaining how MPTCP works and how defenders can identify its use in network traffic.

The article describes MPTCP's primary real-world use case as iOS/iPadOS devices connecting to Apple services (17.0.0.0/8) for Siri and Apple Music, using MPTCP versions 0 and 1. It details the TCP option (0x1e/30) and its subtypes: MP_CAPABLE (handshake capability negotiation), MP_JOIN (adding subflows, potentially from different IPs), DSS (sequence number stitching across subflows), and ADD_ADDR/REMOVE_ADDR (address advertisement). The diary notes that MP_JOIN can be server-initiated per RFC, which has implications for firewall rule design since a server may attempt an additional subflow connection that standard inbound rules might block.

For detection, the article provides practical guidance across common tools: Wireshark/tshark has a native 'mptcp' filter; tcpdump can approximate detection via large TCP header length (tcp[12]>0xd0); Suricata can use tcp.hdr to match the MP_CAPABLE option bytes (1e 14 00 for v0, 1e 14 01 for v1); Snort currently lacks a way to inspect TCP options for this purpose; and Zeek can log MPTCP via its tcp_option event with a simple script snippet. No exploitation details or in-the-wild activity related to the referenced CVE are discussed in this diary; it serves as protocol-awareness and detection-engineering reference material for defenders.

## Mentioned in this report

- Vulnerabilities: CVE-2026-98432

Source reporting: https://isc.sans.edu/diary/rss/33482

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