CVE-2024-56640: Linux kernel · net/smc: fix LGR and link use-after-free issue
Affects Linux kernelSource GCVE Database
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
- 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:HExploitation evidence
Disclosed: evidence found.
CVE published 27 Dec 2024
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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.
Patches and advisories
- ubuntu.com/security/notices/USN-7379-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7380-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7381-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7382-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7388-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7389-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7390-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7379-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7407-1 (opens in a new tab)
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 24.04 LTSlinuxpkg:deb/ubuntu/linux?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azure-6.11pkg:deb/ubuntu/linux-azure-6.11?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-azure-nvidiapkg:deb/ubuntu/linux-azure-nvidia?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
Ubuntu 24.04 LTSlinux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=nobleOther threats | Affected
| Fixed in
|
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
- ubuntu.com/security/CVE-2024-56640 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2024-56640 (opens in a new tab)
- git.kernel.org/linus/2c7f14ed9c19ec0f149479d1c2842ec1f9bf76d7 (opens in a new tab)
- git.kernel.org/stable/c/0cf598548a6c36d90681d53c6b77d52363f2f295 (opens in a new tab)
- git.kernel.org/stable/c/2c7f14ed9c19ec0f149479d1c2842ec1f9bf76d7 (opens in a new tab)
- git.kernel.org/stable/c/673d606683ac70bc074ca6676b938bff18635226 (opens in a new tab)
- git.kernel.org/stable/c/6f0ae06a234a78ae137064f2c89135ac078a00eb (opens in a new tab)
- git.kernel.org/stable/c/f502a88fdd415647a1f2dc45fac71b9c522a052b (opens in a new tab)
- ubuntu.com/security/notices/USN-7379-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7380-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7381-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7382-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7388-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7389-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7390-1 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7387-3 (opens in a new tab)
- ubuntu.com/security/notices/USN-7379-2 (opens in a new tab)
- ubuntu.com/security/notices/USN-7407-1 (opens in a new tab)