CVE-2025-21707: In the Linux kernel, the following vulnerability has been resolved: mptcp: consolidate suboption status MPTCP maintains the received sub-options status is the

In the Linux kernel, the following vulnerability has been resolved: mptcp: consolidate suboption status MPTCP maintains the received sub-options status is the

In the Linux kernel, the following vulnerability has been resolved: mptcp: consolidate suboption status MPTCP maintains the received sub-options status is the bitmask carrying the received suboptions and in several bitfields carrying per suboption additional info. Zeroing the bitmask before parsing is not enough to ensure a consistent status, and the MPTCP code has to additionally clear some bitfiled depending on the actually parsed suboption. The above schema is fragile, and syzbot managed to trigger a path where a relevant bitfield is not cleared/initialized: BUG: KMSAN: uninit-value in __mptcp_expand_seq net/mptcp/options.c:1030 [inline] BUG: KMSAN: uninit-value in mptcp_expand_seq net/mptcp/protocol.h:864 [inline] BUG: KMSAN: uninit-value in ack_update_msk net/mptcp/options.c:1060 [inline] BUG: KMSAN: uninit-value in mptcp_incoming_options+0x2036/0x3d30 net/mptcp/options.c:1209 __mptcp_expand_seq net/mptcp/options.c:1030 [inline] mptcp_expand_seq net/mptcp/protocol.h:864 [inline] ack_update_msk net/mptcp/options.c:1060 [inline] mptcp_incoming_options+0x2036/0x3d30 net/mptcp/options.c:1209 tcp_data_queue+0xb4/0x7be0 net/ipv4/tcp_input.c:5233 tcp_rc

Description from the National Vulnerability Database, published by 416baaa9-dc9f-4396-8d5f-8c081fb06d67

What it means for a small business

Linux is on the computers, phones or browsers your team uses every day. Turn on automatic updates and restart: most of these fixes only take effect after a restart.

How likely is an attack? The Exploit Prediction Scoring System, run by FIRST (the global association of security response teams), puts the odds of this one being exploited in the next 30 days at 0.54%, higher than 45% of CVEs. That’s low, but low isn’t zero, and the odds jump the day someone publishes an exploit. Scored October 29, 2026, updated daily.

Check your own setup

Website check: reads what your site runs from the outside (WordPress version, plugins it can see, old server software) and matches it against this database.
Server check: what your web server says about itself, and whether that version has known flaws.

Sources

Part of the Huttenlocher Technologies vulnerability database, refreshed twice a day from CISA and the NVD. The title, category and plain-language guidance are ours; check the linked record before acting on a detail. This is general guidance, not a review of your systems.

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