CVE-2026-43438: Linux kernel · sched_ext: Remove redundant css_put() in scx_cgroup_init()
Affects Linux kernelSource GCVE Database
Not known to be exploited · CVSS 7.8 High.
Data as of 26 Oct 2026, 12:55 UTC
- EPSS
- 0.1% chance of exploitation in 30 days – higher than 2% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:HExploitation evidence
Disclosed: evidence found.
CVE published 8 May 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: 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 26 Oct 2026.
What to do
Affected software
| Product | Affected | Fixed in |
|---|---|---|
Ubuntu 26.04 LTSlinux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=resoluteOther threats | Affected
| Fixed in– |
Ubuntu 25.10linuxpkg:deb/ubuntu/linux?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-awspkg:deb/ubuntu/linux-aws?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azurepkg:deb/ubuntu/linux-azure?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-azure-fdepkg:deb/ubuntu/linux-azure-fde?arch=source&distro=questingOther threats | Affected
| Fixed in– |
Ubuntu 25.10linux-gcppkg:deb/ubuntu/linux-gcp?arch=source&distro=questingOther 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 fix is available that removes the redundant css_put() call causing the reference count underflow. Users should update to patched versions of the linux-hwe-edge kernel as listed in the affected versions to remediate this vulnerability.
Description
A vulnerability in the Linux kernel sched_ext subsystem was resolved by removing a redundant css_put() call in the scx_cgroup_init() function. The issue arises because the iterator css_for_each_descendant_pre() walks the cgroup hierarchy without incrementing reference counts, yet css_put() was called improperly, causing a reference count underflow. This could lead to a Use-After-Free (UAF) condition. The vulnerability affects specific versions of the linux-hwe-edge kernel. The CVSS score is 7.8, indicating a high impact on confidentiality, integrity, and availability, but the severity is noted as low in the input data. No known exploits are reported in the wild.
References
- ubuntu.com/security/CVE-2026-43438 (opens in a new tab)
- cve.org/CVERecord?id=CVE-2026-43438 (opens in a new tab)
- git.kernel.org/linus/1336b579f6079fb8520be03624fcd9ba443c930b (opens in a new tab)
- git.kernel.org/stable/c/1336b579f6079fb8520be03624fcd9ba443c930b (opens in a new tab)
- git.kernel.org/stable/c/6eaaa67d6998f6c30c462b140db8c062e07ec473 (opens in a new tab)
- git.kernel.org/stable/c/bf50f3285eda8a0173625fcdb5f183f96e1008cd (opens in a new tab)
- git.kernel.org/stable/c/cc095cd305fddbe25a968e4a78436ff9476cf0f6 (opens in a new tab)