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VulnerabilityPublished Updated

CVE-2026-68170: Linux kernel · mptcp: fix stale skb->sk reference on subflow close

Affects Linux kernelSource GCVE Database

0

Not known to be exploited · CVSS 9.8 Critical · fixed in 7.0.0-38.38~24.04.4 : patch Linux kernel as a priority.

Data as of 26 Oct 2026, 14:05 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.5% chance of exploitation in 30 days – higher than 43% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 7.0.0-38.38~24.04.4, 7.0.0-38.38, 7.0.0-1014.14 +11
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponised: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Ubuntu 26.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-38.38
Fixed in
  • 7.0.0-38.38
Ubuntu 26.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1014.14
Fixed in
  • 7.0.0-1014.14
Ubuntu 26.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1017.17
Fixed in
  • 7.0.0-1017.17
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1016.16
Fixed in
  • 7.0.0-1016.16
Ubuntu 26.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1014.14
Fixed in
  • 7.0.0-1014.14
Ubuntu 26.04 LTSlinux-gkepkg:deb/ubuntu/linux-gke?arch=source&distro=resoluteOther threatsAffected
  • <7.0.0-1008.9
Fixed in
  • 7.0.0-1008.9

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix stale skb->sk reference on subflow close The backlog list is updated by mptcp_data_ready() under mptcp_data_lock(). The cleanup of backlog references to a closing subflow, however, was performed in mptcp_close_ssk(), before __mptcp_close_ssk() acquires the ssk lock, and while holding neither the ssk lock nor mptcp_data_lock(). Because that traversal ran without mptcp_data_lock(), concurrent softirq RX processing on another CPU (subflow_data_ready() -> mptcp_data_ready() -> __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog entry referencing the ssk while the cleanup loop was in progress. Such an entry could be missed by the cleanup, or the concurrent list update could corrupt the traversal, leaving skb->sk pointing at the ssk after it is freed. A later mptcp_backlog_purge() then dereferences the stale pointer, triggering a warning in inet_sock_destruct() (ssk->sk_rmem_alloc != 0) followed by a use-after-free in mptcp_backlog_purge(). Fix this by moving the backlog cleanup into __mptcp_close_ssk(), after subflow->closing is set to 1 and while the ssk lock is still held, serialized under mptcp_data_lock(). The cleanup runs only on the push path (MPTCP_CF_PUSH), where backlog references accumulate; on other teardown paths the caller already handles cleanup. With subflow->closing set and mptcp_data_lock() held across the purge, any concurrent mptcp_data_ready() either completes its enqueue before the purge runs and is caught, or observes closing=1 and bails out. Once mptcp_data_unlock() is reached, no new skb referencing the ssk can be enqueued, so the cleanup is exhaustive. Remove the unprotected traversal from mptcp_close_ssk() entirely.

References

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