CVE-2026-43323 [Medium] | Security Vulnerability in Linux Kernel

In the Linux kernel, the following vulnerability has been resolved: sched/fair: Fix zero_vruntime tracking fix John reported that stress-ng-yield could make his machine unhappy and managed to bisect it to commit b3d99f43c72b ("sched/fair: Fix zero_vruntime tracking"). The combination of yield and that commit was specific enough to hypothesize the following scenario: Suppose we have 2 runnable tasks, both doing yield. Then one will be eligible and one will not be, because the average position must be in between these two entities. Therefore, the runnable task will be eligible, and be promoted a full slice (all the tasks do is yield after all). This causes it to jump over the other task and now the other task is eligible and current is no longer. So we schedule. Since we are runnable, there is no {de,en}queue. All we have is the __{en,de}queue_entity() from {put_prev,set_next}_task(). But per the fingered commit, those two no longer move zero_vruntime. All that moves zero_vruntime are tick and full {de,en}queue. This means, that if the two tasks playing leapfrog can reach the critical speed to reach the overflow point inside one tick's worth of time, we're up a creek. Additionally, when multiple cgroups are involved, there is no guarantee the tick will in fact hit every cgroup in a timely manner. Statistically speaking it will, but that same statistics does not rule out the possibility of one cgroup not getting a tick for a significant amount of time -- however unlikely. Therefore, just like with the yield() case, force an update at the end of every slice. This ensures the update is never more than a single slice behind and the whole thing is within 2 lag bounds as per the comment on entity_key().

#	Date	Old EPSS score	New EPSS score	Delta (New - Old)
1	2026-05-09	—	0.02%	—

Date

Old EPSS score

New EPSS score

Delta (New - Old)

2026-05-09

—

0.02%

—

Base score	Version	Severity	Vector	Exploitability	Impact	Score source
5.5	3.1	MEDIUM	`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H` Click to expand Attack vector (AV:L) They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by. Attack complexity (AC:L) Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup. Privileges required (PR:L) A normal user session is enough; they don’t have to be admin. User interaction (UI:N) Nobody has to click “OK” or open a trap file; it can work without a victim helping. Scope (S:U) Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems. Confidentiality (C:N) Doesn’t really leak secrets in a meaningful way. Integrity (I:N) Data isn’t meaningfully altered or forged. Availability (A:H) Could take the service down hard or make it unusable for people who depend on it.	1.8	3.6	[email protected]

Base score

Version

Severity

Vector

Exploitability

Impact

Score source

5.5

3.1

MEDIUM

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand

Attack vector (AV:L): They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L): Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L): A normal user session is enough; they don’t have to be admin.
User interaction (UI:N): Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U): Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N): Doesn’t really leak secrets in a meaningful way.
Integrity (I:N): Data isn’t meaningfully altered or forged.
Availability (A:H): Could take the service down hard or make it unusable for people who depend on it.

1.8

3.6

[email protected]

OS Trackers for CVE-2026-43323

vendor	priority	summary	link
`debian`	unimportant	CVE-2026-43323 unimportant priority: Debian including 1 source packages (linux), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5.	https://security-tracker.debian.org/tracker/CVE-2026-43323
`suse`	medium	CVE-2026-43323 severity moderate: SUSE including 21 source package names (cluster-md-kmp-default, dlm-kmp-default, …), 198 product×package rows across 39 product lines (SUSE Linux Enterprise High Availability Extension 15 SP7, SUSE Linux Enterprise High Performance Computing 15 SP4-LTSS, … (39 product lines)): Known Not Affected 198.	https://www.suse.com/security/cve/CVE-2026-43323/
`ubuntu`	medium	CVE-2026-43323 medium priority: Ubuntu including 161 source packages (linux, linux-allwinner-5.19, …), 1449 status rows across 9 suites (bionic, focal, jammy, noble, questing, resolute, trusty, upstream, xenial): DNE 1047, ignored 169, not-affected 144, released 84, needs-triage 5.	https://ubuntu.com/security/CVE-2026-43323

Affected software / configurations for CVE-2026-43323

Vendor	Product	Version	Raw CPE
linux	linux_kernel	>= 6.12.78, < 6.12.81	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.18.17, < 6.18.22	cpe:2.3:o:linux:linux_kernel::::::::
linux	linux_kernel	>= 6.19.7, < 6.19.12	cpe:2.3:o:linux:linux_kernel::::::::

References for CVE-2026-43323

URL	Tags
https://git.kernel.org/stable/c/1319ea57529e131822bab56bf417c8edc2db9ae8	Patch
https://git.kernel.org/stable/c/87573883c30f1a8555ff720836bb6ea231058539	Patch
https://git.kernel.org/stable/c/c089147074ed96ff4330739a0559394c19a3dfc8	Patch
https://git.kernel.org/stable/c/fb61ffb3fb30a161eb5404c27fc7635e275beafd	Patch

URL

CVE-2026-43323 | sched/fair: Fix zero_vruntime tracking fix

Exploit prediction scoring system (EPSS) score for CVE-2026-43323

Common vulnerability scoring system (CVSS) metrics for CVE-2026-43323

Weakness enumeration for CVE-2026-43323

GitHub Security Advisory for CVE-2026-43323

OS Trackers for CVE-2026-43323

Affected software / configurations for CVE-2026-43323

References for CVE-2026-43323