critical 9.8

CVE-2025-21707 in the critical feed json

mptcp: consolidate suboption status

published 2025-02-27 20 mo ago modified 2026-10-15 25 d ago also EUVD-2025-5243

cvss: 9.8; version 3.1, CNA
cisa kev: Not listed; not in CISA's catalog
epss: 0.5%; EPSS 0.5% chance of exploitation in 30 days, percentile 45%
public exploits: 0; none known

In the Linux kernel, the following vulnerability has been resolved:

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_rcv_established+0x1061/0x2510 net/ipv4/tcp_input.c:6264 tcp_v4_do_rcv+0x7f3/0x11a0 net/ipv4/tcp_ipv4.c:1916 tcp_v4_rcv+0x51df/0x5750 net/ipv4/tcp_ipv4.c:2351 ip_protocol_deliver_rcu+0x2a3/0x13d0 net/ipv4/ip_input.c:205 ip_local_deliver_finish+0x336/0x500 net/ipv4/ip_input.c:233 NF_HOOK include/linux/netfilter.h:314 [inline] ip_local_deliver+0x21f/0x490 net/ipv4/ip_input.c:254 dst_input include/net/dst.h:460 [inline] ip_rcv_finish+0x4a2/0x520 net/ipv4/ip_input.c:447 NF_HOOK include/linux/netfilter.h:314 [inline] ip_rcv+0xcd/0x380 net/ipv4/ip_input.c:567 __netif_receive_skb_one_core net/core/dev.c:5704 [inline] __netif_receive_skb+0x319/0xa00 net/core/dev.c:5817 process_backlog+0x4ad/0xa50 net/core/dev.c:6149 __napi_poll+0xe7/0x980 net/core/dev.c:6902 napi_poll net/core/dev.c:6971 [inline] net_rx_action+0xa5a/0x19b0 net/core/dev.c:7093 handle_softirqs+0x1a0/0x7c0 kernel/softirq.c:561 __do_softirq+0x14/0x1a kernel/softirq.c:595 do_softirq+0x9a/0x100 kernel/softirq.c:462 __local_bh_enable_ip+0x9f/0xb0 kernel/softirq.c:389 local_bh_enable include/linux/bottom_half.h:33 [inline] rcu_read_unlock_bh include/linux/rcupdate.h:919 [inline] __dev_queue_xmit+0x2758/0x57d0 net/core/dev.c:4493 dev_queue_xmit include/linux/netdevice.h:3168 [inline] neigh_hh_output include/net/neighbour.h:523 [inline] neigh_output include/net/neighbour.h:537 [inline] ip_finish_output2+0x187c/0x1b70 net/ipv4/ip_output.c:236 __ip_finish_output+0x287/0x810 ip_finish_output+0x4b/0x600 net/ipv4/ip_output.c:324 NF_HOOK_COND include/linux/netfilter.h:303 [inline] ip_output+0x15f/0x3f0 net/ipv4/ip_output.c:434 dst_output include/net/dst.h:450 [inline] ip_local_out net/ipv4/ip_output.c:130 [inline] __ip_queue_xmit+0x1f2a/0x20d0 net/ipv4/ip_output.c:536 ip_queue_xmit+0x60/0x80 net/ipv4/ip_output.c:550 __tcp_transmit_skb+0x3cea/0x4900 net/ipv4/tcp_output.c:1468 tcp_transmit_skb net/ipv4/tcp_output.c:1486 [inline] tcp_write_xmit+0x3b90/0x9070 net/ipv4/tcp_output.c:2829 __tcp_push_pending_frames+0xc4/0x380 net/ipv4/tcp_output.c:3012 tcp_send_fin+0x9f6/0xf50 net/ipv4/tcp_output.c:3618 __tcp_close+0x140c/0x1550 net/ipv4/tcp.c:3130 __mptcp_close_ssk+0x74e/0x16f0 net/mptcp/protocol.c:2496 mptcp_close_ssk+0x26b/0x2c0 net/mptcp/protocol.c:2550 mptcp_pm_nl_rm_addr_or_subflow+0x635/0xd10 net/mptcp/pm_netlink.c:889 mptcp_pm_nl_rm_subflow_received net/mptcp/pm_netlink.c:924 [inline] mptcp_pm_flush_addrs_and_subflows net/mptcp/pm_netlink.c:1688 [inline] mptcp_nl_flush_addrs_list net/mptcp/pm_netlink.c:1709 [inline] mptcp_pm_nl_flush_addrs_doit+0xe10/0x1630 net/mptcp/pm_netlink.c:1750 genl_family_rcv_msg_doit net/netlink/genetlink.c:1115 [inline]

---truncated---

Patch / fix

fixed in 1 distros 4 links 6

Linux Linux 5.15.179, 6.1.129, 6.6.76, 6.12.13, 6.13.2, 6.14

debian ubuntu suse azure linux

linux Debian 12 6.1.129-1
linux Debian 14, Debian 13 6.12.13-1

debian advisories DEBIAN-CVE-2025-21707

linux Ubuntu 22.04 LTS 5.15.0-140.150
linux Ubuntu 24.04 LTS 6.8.0-64.67
linux-aws Ubuntu 22.04 LTS 5.15.0-1084.91
linux-aws Ubuntu 24.04 LTS 6.8.0-1032.34
linux-gcp Ubuntu 22.04 LTS 5.15.0-1083.92
linux-gcp Ubuntu 24.04 LTS 6.8.0-1033.35
linux-gke Ubuntu 22.04 LTS 5.15.0-1081.87
linux-gke Ubuntu 24.04 LTS 6.8.0-1028.32

ubuntu advisories UBUNTU-CVE-2025-21707

Ubuntu security data © Canonical Ltd., from https://github.com/canonical/ubuntu-security-notices via OSV; changed: normalised to fixed package versions per release. CC BY-SA 4.0

kernel-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
kernel-syms-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
kernel-rt_debug Real Time Module 15 SP7 6.4.0-150700.7.3.1
kernel-source-rt Real Time Module 15 SP7 6.4.0-150700.7.3.1
kernel-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
kernel-syms-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
kernel-source-azure SLE Module for Public Cloud 15 SP7 6.4.0-150700.20.3.1
kernel-rt Real Time Module 15 SP6, openSUSE Leap 15.6 6.4.0-150600.10.39.1

suse advisories SUSE-SU-2025:01972-1 SUSE-SU-2025:01967-1 SUSE-SU-2025:01964-1 SUSE-SU-2025:01951-1 SUSE-SU-2025:01919-1 SUSE-SU-2025:01707-1

kernel CBL-Mariner 2.0 5.15.179.1-1

azure linux advisories AZL-57978

Azure Linux vulnerability data, Copyright (c) Microsoft Corporation, from https://github.com/microsoft/AzureLinuxVulnerabilityData via OSV, under the MIT licence; changed: normalised to fixed package versions per release. MIT

Vendor advisories

What the vendors themselves say about their products: affected, fixed or not affected, and what to do.

red hat product security vex CVE-2025-21707 updated 2026-11-07 cvss 5.5

kernel: mptcp: consolidate suboption status

Red Hat Enterprise Linux 8 perf, kernel, bpftool, kernel-rt, kernel-core, kernel-tools, +29 more
affected: no fix planned “Out of support scope”
Red Hat Enterprise Linux 9 rv, perf, rtla, kernel, bpftool, libperf, +82 more Red Hat Enterprise Linux 10 kernel
affected: no fix planned “Will not fix”
Red Hat Enterprise Linux 6 perf, kernel, python-perf, kernel-kdump, kernel-firmware, kernel-bootwrapper, +1 more Red Hat Enterprise Linux 7 perf, kernel, bpftool, kernel-rt, python-perf, kernel-kdump, +8 more
not affected: vulnerable code not present

Red Hat CSAF VEX © Red Hat, Inc., from https://security.access.redhat.com/data/csaf/v2/vex/; changed: reduced to product statuses and remediations. CC BY 4.0 · csaf

cisa ICSA-26-295-11 updated 2026-10-22 cvss 9.8

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.7 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.7 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.7
affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-26-295-16 updated 2026-10-22 cvss 9.8

Siemens SIMATIC S7-1500 TM MFP

Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

cisa ICSA-26-209-04 updated 2026-07-28 cvss 5.5

Siemens SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP

Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= 3.1.6 Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AC0) >= 3.1.6 Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP (6AG1518-4AX00-4AC0) >= 3.1.6
affected: mitigation, no fix available

Facts from CISA's republication of the vendor's own advisory (CSAF); the linked advisory is the authoritative source. CISA notification · csaf

Exploit prediction

0.54% chance of exploitation in the next 30 days, higher than 45% of all scored CVEs (FIRST EPSS, 2026-11-08).

CVSS scores

assigned by	version	score	vector
CNA	3.1	9.8	CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
NVD	3.1	5.5	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected products

Linux Linux
Siemens SIMATIC S7-1500 CPU 1518-4 PN/DP MFP
Siemens SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP
Siemens SIMATIC S7-1500 TM MFP - GNU/Linux subsystem
Siemens SIPLUS S7-1500 CPU 1518-4 PN/DP MFP

Classification

Weakness

CWE-908 Use of Uninitialized Resource

Technology feeds

Linux kernel rss critical rss

References

Sources

CVE List CVE-2025-21707
NVD CVE-2025-21707

Fencer Vulns keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

Summary

Patch / fix

Vendor advisories

Exploit prediction

CVSS scores

Affected products

Classification

References

Sources