SANS Explains Multipath TCP Detection
SANS ISC explains Multipath TCP (MPTCP) mechanics and detection techniques, prompted by a new Linux kernel MPTCP vulnerability.
Sourceisc.sans.edu — open the original
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
Source reporting: https://isc.sans.edu/diary/rss/33482
Free public brief. Slack alerts on the vendors you run come with the paid plans, and a new account gets three days of them, no card.
What this brief leaves out
This page is the free tier: the write-up, the severity, the names. In the app the same report carries live profiles of the CVEs it names. The paid plans add the security research and news reporting the free tier leaves out.
It sits in a corpus of 16,436 reports from 149 sources, 661 of them written in the last seven days, and it grows through the day.
A new account starts with three days of all of it, no card, then keeps the government and CERT reporting free. Slack alerts are a paid-plan feature: name the vendors you run and Slack hears about the reports that touch them, not the rest of the week's. Nothing is charged unless you subscribe.
Create a free account What it costs