CVE-2026-23321

MEDIUMNVD 5.55.5—
EchelonGraph scoreMEDIUM confidence

Score 5.5 from GitHub Security Advisory published 2026-03-25. NVD baseline CVSS 5.5; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: epss, ghsa, nvd
5.5EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
  • Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.5Exploit: None knownExposed: 0

A fix is available — apply it.

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

mptcp: pm: in-kernel: always mark signal+subflow endp as used

Syzkaller managed to find a combination of actions that was generating this warning:

msk->pm.local_addr_used == 0 WARNING: net/mptcp/pm_kernel.c:1071 at __mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline], CPU#1: syz.2.17/961 WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1103 [inline], CPU#1: syz.2.17/961 WARNING: net/mptcp/pm_kernel.c:1071 at mptcp_pm_nl_del_addr_doit+0x81d/0x8f0 net/mptcp/pm_kernel.c:1210, CPU#1: syz.2.17/961 Modules linked in: CPU: 1 UID: 0 PID: 961 Comm: syz.2.17 Not tainted 6.19.0-08368-gfafda3b4b06b #22 PREEMPT(full) Hardware name: QEMU Ubuntu 25.10 PC v2 (i440FX + PIIX, + 10.1 machine, 1996), BIOS 1.17.0-debian-1.17.0-1build1 04/01/2014 RIP: 0010:__mark_subflow_endp_available net/mptcp/pm_kernel.c:1071 [inline] RIP: 0010:mptcp_nl_remove_subflow_and_signal_addr net/mptcp/pm_kernel.c:1103 [inline] RIP: 0010:mptcp_pm_nl_del_addr_doit+0x81d/0x8f0 net/mptcp/pm_kernel.c:1210 Code: 89 c5 e8 46 30 6f fe e9 21 fd ff ff 49 83 ed 80 e8 38 30 6f fe 4c 89 ef be 03 00 00 00 e8 db 49 df fe eb ac e8 24 30 6f fe 90 <0f> 0b 90 e9 1d ff ff ff e8 16 30 6f fe eb 05 e8 0f 30 6f fe e8 9a RSP: 0018:ffffc90001663880 EFLAGS: 00010293 RAX: ffffffff82de1a6c RBX: 0000000000000000 RCX: ffff88800722b500 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000000 RBP: ffff8880158b22d0 R08: 0000000000010425 R09: ffffffffffffffff R10: ffffffff82de18ba R11: 0000000000000000 R12: ffff88800641a640 R13: ffff8880158b1880 R14: ffff88801ec3c900 R15: ffff88800641a650 FS: 00005555722c3500(0000) GS:ffff8880f909d000(0000) knlGS:0000000000000000 CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 CR2: 00007f66346e0f60 CR3: 000000001607c000 CR4: 0000000000350ef0 Call Trace: genl_family_rcv_msg_doit+0x117/0x180 net/netlink/genetlink.c:1115 genl_family_rcv_msg net/netlink/genetlink.c:1195 [inline] genl_rcv_msg+0x3a8/0x3f0 net/netlink/genetlink.c:1210 netlink_rcv_skb+0x16d/0x240 net/netlink/af_netlink.c:2550 genl_rcv+0x28/0x40 net/netlink/genetlink.c:1219 netlink_unicast_kernel net/netlink/af_netlink.c:1318 [inline] netlink_unicast+0x3e9/0x4c0 net/netlink/af_netlink.c:1344 netlink_sendmsg+0x4aa/0x5b0 net/netlink/af_netlink.c:1894 sock_sendmsg_nosec net/socket.c:727 [inline] __sock_sendmsg+0xc9/0xf0 net/socket.c:742 ____sys_sendmsg+0x272/0x3b0 net/socket.c:2592 ___sys_sendmsg+0x2de/0x320 net/socket.c:2646 __sys_sendmsg net/socket.c:2678 [inline] __do_sys_sendmsg net/socket.c:2683 [inline] __se_sys_sendmsg net/socket.c:2681 [inline] __x64_sys_sendmsg+0x110/0x1a0 net/socket.c:2681 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0x143/0x440 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f66346f826d Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffc83d8bdc8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f6634985fa0 RCX: 00007f66346f826d RDX: 00000000040000b0 RSI: 0000200000000740 RDI: 0000000000000007 RBP: 0000000000000000 R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 00007f6634985fa8 R13: 00007f6634985fac R14: 0000000000000000 R15: 0000000000001770

The actions that caused that seem to be:

  • Set the MPTCP subflows limit to 0
  • Create an MPTCP endpoint with both the 'signal' and 'subflow' flags
  • Create a new MPTCP connection from a different address: an ADD_ADDR
linked to the MPTCP endpoint will be sent ('signal' flag), but no subflows is initiated ('subflow' flag)
  • Remove the MPTCP endpoint

---truncated---

CVSS v3
5.5
EG Score
5.5(medium)
EG Risk
29(Track)
EG Risk 29/100SSVC: Track

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity55% × 45%
Exploitation0% × 40%
Automatability30% × 15%
Action: Routine — remediate on your standard cadence.
EPSS PROB
0%
EPSS %ILE
2%
KEV
Not listed

Published

March 25, 2026

Last Modified

September 8, 2026

Advisory Details (8)

Auto-updated Jul 19, 2026
⚠️ Active exploitation confirmed. No patch confirmed yet.
generic🔴 Active Exploitation

SSA-082556

https://cert-portal.siemens.com/productcert/html/ssa-082556.html
generic

SSA-019113

https://cert-portal.siemens.com/productcert/html/ssa-019113.html
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/c5c877e140e5f46023a74a51e577ce5edd0a4be7
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/a64aa7db39392add5be09dffaedbf1f0ce5554df
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/67f34ab318807989b57dfdb0f79e2d4e57018290
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/579a752464a64cb5f9139102f0e6b90a1f595ceb
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/198824ccfa64ffebd918bf99c939bd8170a4a4d8
generic

mptcp: pm: in-kernel: always mark signal+subflow endp as used - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/05799c2f1ca5eb13d65764dda688d02021b65e06

Vendor Advisories for CVE-2026-23321(1)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(15)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-tools-aws-lts-24.04 (6.8.0-1061.64+1) @ noble2026-09-08ubuntu
ubuntulinux-tools-azure-lts-24.04 (6.8.0-1063.71) @ noble2026-09-08ubuntu
ubuntulinux-tools-raspi-realtime-6.8 (6.8.0-2050.52) @ noble2026-09-08ubuntu
ubuntulinux-virtual-6.8 (6.8.0-136.136) @ noble2026-09-08ubuntu
ubuntulinux-tools-gcp-fips-6.8 (6.8.0-1064.72+fips1) @ noble2026-09-08ubuntu
ubuntulinux-tools-lowlatency-hwe-22.04-edge (6.8.0-136.136.2~22.04.1) @ jammy2026-09-08ubuntu
ubuntulinux-tools-oracle-edge (6.8.0-1058.61~22.04.1) @ jammy2026-09-08ubuntu
ubuntulinux-tools-nvidia-lowlatency-64k-6.8 (6.8.0-1059.62.1) @ noble2026-09-08ubuntu
ubuntulinux-tools-azure-fde-lts-24.04 (6.8.0-1062.69) @ noble2026-09-08ubuntu
ubuntulinux-tools-azure-fips-6.8 (6.8.0-1063.71+fips2) @ noble2026-09-08ubuntu
ubuntulinux-tools-azure-fde-6.8 (6.8.0-1062.69~22.04.1) @ jammy2026-09-08ubuntu
ubuntulinux-tools-aws-fips-6.8 (6.8.0-1061.64+fips1) @ noble2026-09-08ubuntu
ubuntulinux-xilinx-zynqmp (6.8.0.1033.34) @ noble2026-09-08ubuntu
ubuntulinux-virtual-hwe-22.04-edge (6.8.0-136.136~22.04.1) @ jammy2026-09-08ubuntu
linuxKernel @ 6.1.167—osv

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Affected Packages

(4 across 4 ecosystems)
Debian:11(1)
PackageVulnerable rangeFixed inDependents
linux-6.16.1.106-3~deb11u1 ... 6.1.164-1~deb11u1 (16 versions)6.1.170-1~deb11u1—
Debian:12(1)
PackageVulnerable rangeFixed inDependents
linux6.1.106-1 ... 6.1.99-1 (48 versions)6.1.170-1—
Debian:13(1)
PackageVulnerable rangeFixed inDependents
linux6.12.38-1 ... 6.12.85-1~bpo12+1 (17 versions)6.12.85-1—
Debian:14(1)
PackageVulnerable rangeFixed inDependents
linux6.12.100-1 ... 6.19~rc8-1~exp1 (120 versions)6.19.8-1—

All Vendor Advisories

(14)

Every vendor that published an advisory referencing this CVE — pulled from our cve_vendor_advisories aggregation. Click any row for the vendor's original advisory page.

Data Freshness Timeline

(refreshed 4× in last 7d / 27× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 213 total refreshes for this CVE.

  1. 2026-09-18 19:27 UTCEPSS rescore
  2. 2026-09-16 14:07 UTCEPSS rescore
  3. 2026-09-16 05:15 UTCEPSS rescore
  4. 2026-09-13 16:47 UTCEPSS rescore
  5. 2026-09-12 15:01 UTCEPSS rescore
  6. 2026-09-11 14:52 UTCEPSS rescore
  7. 2026-09-10 09:34 UTCEPSS rescore
  8. 2026-09-08 22:00 UTCEPSS rescore
  9. 2026-09-08 09:16 UTCEG score recompute
  10. 2026-09-08 09:16 UTCVendor advisory
  11. 2026-09-08 09:15 UTCGHSA enrichment
  12. 2026-09-07 16:01 UTCEPSS rescore
  13. 2026-09-06 13:47 UTCEPSS rescore
  14. 2026-09-06 13:47 UTCEPSS rescore
  15. 2026-09-04 05:06 UTCEPSS rescore
  16. 2026-09-02 15:01 UTCOSV refresh
  17. 2026-09-02 14:11 UTCEPSS rescore
  18. 2026-09-01 13:53 UTCEPSS rescore
  19. 2026-09-01 04:39 UTCEPSS rescore
  20. 2026-08-30 19:17 UTCEPSS rescore
  21. 2026-08-30 01:22 UTCEPSS rescore
  22. 2026-08-28 21:41 UTCEPSS rescore
  23. 2026-08-27 14:25 UTCEPSS rescore
  24. 2026-08-26 14:46 UTCEPSS rescore
  25. 2026-08-25 13:48 UTCEPSS rescore
Show 75 more
  1. 2026-08-23 00:19 UTCEPSS rescore
  2. 2026-08-21 23:49 UTCEPSS rescore
  3. 2026-08-20 22:55 UTCEPSS rescore
  4. 2026-08-19 17:03 UTCEPSS rescore
  5. 2026-08-18 13:48 UTCEPSS rescore
  6. 2026-08-17 13:47 UTCEPSS rescore
  7. 2026-08-16 14:56 UTCEPSS rescore
  8. 2026-08-16 10:25 UTCEG score recompute
  9. 2026-08-16 10:25 UTCVendor advisory
  10. 2026-08-16 10:25 UTCGHSA enrichment
  11. 2026-08-16 02:14 UTCEPSS rescore
  12. 2026-08-15 01:30 UTCEPSS rescore
  13. 2026-08-14 06:44 UTCEG score recompute
  14. 2026-08-14 06:44 UTCVendor advisory
  15. 2026-08-14 06:44 UTCGHSA enrichment
  16. 2026-08-13 22:00 UTCEPSS rescore
  17. 2026-08-12 20:59 UTCEG score recompute
  18. 2026-08-12 20:59 UTCVendor advisory
  19. 2026-08-12 20:59 UTCGHSA enrichment
  20. 2026-08-12 13:50 UTCEPSS rescore
  21. 2026-08-11 13:42 UTCEPSS rescore
  22. 2026-08-11 04:41 UTCEG score recompute
  23. 2026-08-11 04:41 UTCVendor advisory
  24. 2026-08-11 04:41 UTCGHSA enrichment
  25. 2026-08-11 00:00 UTCEPSS rescore
  26. 2026-08-10 05:30 UTCEG score recompute
  27. 2026-08-10 05:30 UTCVendor advisory
  28. 2026-08-10 05:30 UTCGHSA enrichment
  29. 2026-08-09 13:46 UTCEPSS rescore
  30. 2026-08-09 06:20 UTCEG score recompute
  31. 2026-08-09 06:20 UTCVendor advisory
  32. 2026-08-09 06:20 UTCGHSA enrichment
  33. 2026-08-08 16:37 UTCEPSS rescore
  34. 2026-08-07 16:36 UTCEG score recompute
  35. 2026-08-07 16:36 UTCVendor advisory
  36. 2026-08-07 16:36 UTCGHSA enrichment
  37. 2026-08-06 13:46 UTCEPSS rescore
  38. 2026-08-06 01:06 UTCEG score recompute
  39. 2026-08-06 01:06 UTCVendor advisory
  40. 2026-08-06 01:05 UTCGHSA enrichment
  41. 2026-08-05 19:17 UTCEPSS rescore
  42. 2026-08-04 15:10 UTCEPSS rescore
  43. 2026-08-04 10:38 UTCEPSS rescore
  44. 2026-08-03 23:51 UTCEG score recompute
  45. 2026-08-03 23:51 UTCVendor advisory
  46. 2026-08-03 23:51 UTCGHSA enrichment
  47. 2026-08-03 10:35 UTCEPSS rescore
  48. 2026-08-02 15:39 UTCEG score recompute
  49. 2026-08-02 15:39 UTCVendor advisory
  50. 2026-08-02 15:39 UTCGHSA enrichment
  51. 2026-08-02 02:26 UTCEPSS rescore
  52. 2026-08-01 04:15 UTCEPSS rescore
  53. 2026-07-30 01:30 UTCEPSS rescore
  54. 2026-07-27 14:13 UTCEPSS rescore
  55. 2026-07-26 14:54 UTCEPSS rescore
  56. 2026-07-26 14:54 UTCEPSS rescore
  57. 2026-07-25 14:17 UTCEPSS rescore
  58. 2026-07-25 14:17 UTCEPSS rescore
  59. 2026-07-24 14:17 UTCEPSS rescore
  60. 2026-07-23 14:18 UTCEPSS rescore
  61. 2026-07-23 14:18 UTCEPSS rescore
  62. 2026-07-23 03:07 UTCEG score recompute
  63. 2026-07-22 14:08 UTCEPSS rescore
  64. 2026-07-21 15:24 UTCEPSS rescore
  65. 2026-07-21 15:24 UTCEPSS rescore
  66. 2026-07-20 17:08 UTCEPSS rescore
  67. 2026-07-19 14:31 UTCEPSS rescore
  68. 2026-07-19 14:31 UTCEPSS rescore
  69. 2026-07-19 02:29 UTCEPSS rescore
  70. 2026-07-19 02:28 UTCEPSS rescore
  71. 2026-07-18 10:04 UTCEPSS rescore
  72. 2026-07-18 10:04 UTCEPSS rescore
  73. 2026-07-17 07:16 UTCOSV refresh
  74. 2026-07-16 17:03 UTCEPSS rescore
  75. 2026-07-16 17:03 UTCEPSS rescore

Frequently asked(5)

What is CVE-2026-23321?
CVE-2026-23321 is a medium vulnerability published on March 25, 2026. In the Linux kernel, the following vulnerability has been resolved: mptcp: pm: in-kernel: always mark signal+subflow endp as used Syzkaller managed to find a combination of actions that was generating this warning: msk->pm.localaddrused == 0 WARNING: net/mptcp/pmkernel.c:1071 at…
When was CVE-2026-23321 disclosed?
CVE-2026-23321 was first published in the National Vulnerability Database on March 25, 2026, with the most recent update on September 8, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-23321 actively exploited?
CVE-2026-23321 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 97.6% of all scored CVEs.
What is the CVSS score of CVE-2026-23321?
CVE-2026-23321 has a CVSS v3 base score of 5.5 (NVD).
How do I remediate CVE-2026-23321?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-23321, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

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