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VulnerabilityPublished Updated

CVE-2024-56640: Linux kernel · net/smc: fix LGR and link use-after-free issue

Affects Linux kernelSource GCVE Database

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Not known to be exploited · CVSS 9.8 Critical · fixed in 5.4.0-1156.166~18.04.1 : patch Linux kernel as a priority.

Data as of 12 Nov 2026, 19:11 UTC

CVSS 3.1 base score
9.8Critical
How severe the flaw is on the 0–10 CVSS scale.
Patch
Available – fixed in 5.4.0-1156.166~18.04.1, 5.4.0-1161.167~18.04.1, 5.4.0-1159.168~18.04.1 +83
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 27 Dec 2024

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: 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 12 Nov 2026.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

ProductAffectedFixed in
Ubuntu 24.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=nobleOther threatsAffected
  • <6.8.0-58.60
Fixed in
  • 6.8.0-58.60
Ubuntu 24.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=nobleOther threatsAffected
  • <6.8.0-1027.29
Fixed in
  • 6.8.0-1027.29
Ubuntu 24.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=nobleOther threatsAffected
  • <6.8.0-1027.32
Fixed in
  • 6.8.0-1027.32
Ubuntu 24.04 LTSlinux-azure-6.11pkg:deb/ubuntu/linux-azure-6.11?arch=source&distro=nobleOther threatsAffected
  • <6.11.0-1012.12~24.04.1
Fixed in
  • 6.11.0-1012.12~24.04.1
Ubuntu 24.04 LTSlinux-azure-nvidiapkg:deb/ubuntu/linux-azure-nvidia?arch=source&distro=nobleOther threatsAffected
  • <6.8.0-1014.15
Fixed in
  • 6.8.0-1014.15
Ubuntu 24.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=nobleOther threatsAffected
  • <6.8.0-1028.30
Fixed in
  • 6.8.0-1028.30

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

AI-suggested

A patch is available and has been released in multiple fixed Linux kernel versions including 5.4.0-1156.166~18.04.1 and later. Users should update to these fixed kernel versions or later to remediate this vulnerability. No additional mitigation is required beyond applying the official kernel updates.

Description

CVE-2024-56640 is a critical use-after-free vulnerability in the Linux kernel's net/smc subsystem. The flaw arises from premature decrement of reference counts on LGR/link objects, leading to unsafe resource access. The root cause is repeated release of LGR/link refcounts, partly due to missing socket lock protection in the server listening path. This issue has been fixed by adding sock lock protection in the smc_listen_work() path to prevent concurrent connection operations from causing refcount underflow.

References

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