CVE-2026-98163: cgroup: Avoid iteration of dying tasks with zero refcount

High 7.0 EPSS 0.1% Linux kernel

In the Linux kernel, the following vulnerability has been resolved: cgroup: Avoid iteration of dying tasks with zero refcount The commit 260fbcb92bbea ("cgroup: Move dying_tasks cleanup from cgroup_task_release() to cgroup_task_free()") extended the lifetime of tasks on the dying_tasks list. The iterators have provision to go through dying_tasks because of dying threadgroup leaders or explicit CSS_TASK_ITER_WITH_DEAD, however, it was expected that such tasks can obtain a new reference (that is possible before cgroup_task_release()/put_task_struct_rcu_user()). The tasks after cgroup_task_release() and before cgroup_task_free() are subject to race when they may or may not have ->usage count > 0. The race window is between css_task_iter_next() invocations when css_set_lock is released and we may arrive at a new ->task_pos. The iterator should not attempt to resurrect tasks whose ->usage count dropped to zero. (When that happens, __put_task_struct_rcu_cb() is already imminent and the returned task_struct would could be used after free.) As for the fix, we cannot simply check the signal->live count of a task on the dying list because that won't distinguish regular zombies waiting to be reaped from RCU remnant tasks that are going to be free'd. Therefore add an extra check to rule out ->usage==0 tasks from any iteration. The repeat: loop in css_task_iter_advance() doesn't consider ->usage count, so add a new loop to css_task_iter_next() to skip de-used tasks on the dying_list. Rough illustration of the possible race R (reader of cgroup.procs) T (thread) L (group leader) --------------------------------- -------------------------------- -------------------------------- L exits, signal->live > 0 cgroup_task_dead(L) css_set_skip_task_iters() // skips only cset->tasks list_add_tail(&L->cg_list, &cset->dying_tasks) css_task_iter_next() take css_set_lock css_task_iter_advance() leader && signal->live != 0 => it->task_pos = &L->cg_list release css_set_lock T exits --signal->live == 0 cgroup_task_dead(T) // css_set_lock release_task(T) cgroup_task_release(T) release_task(L) // zap_leader cgroup_task_release(L) put_task_struct_rcu_user(L) ...RCU... put_task_struct(L) L->usage = 0 /* L still on dying_tasks */ ...RCU... __put_task_struct(L) css_task_iter_next() // another iteration take css_set_lock it->task_pos = &L->cg_list get_task_struct(L) => addition on 0 drop css_set_lock cgroup_task_free(L) css_set_skip_task_iters() // dying skip comes too late free_task(L) cgroup_procs_show() task_pid_vnr(L)

• CVE-2026-98163CVE identifier
• 7.0CVSS 3.1 base score (high)
• 0.1%EPSS: chance of exploitation in the next 30 days (higher than 1% of CVEs)
• 2026-09-26published

What do these terms mean? CVE · CVSS score · exploited (KEV) · EPSS · backported fix · all terms

Affected and fixed versions

Affected:

• Linux Linux 260fbcb92bbeacfcd050410fdc2d24ab15044400 to before 828938118d6c2bb711301748c3e39e4bed6a62f5
• Linux Linux 260fbcb92bbeacfcd050410fdc2d24ab15044400 to before 057dac23d329d5c5ed62352f2659a39fd46c6d4a
• Linux Linux 6.19

Patch it

Use the commands for your system. Distribution packages often keep an older version number with the fix backported, so compare with the fixed package versions in the table below, not only with the upstream version.

sudo apt update
sudo apt install --only-upgrade linux-image-amd64

sudo apt update
sudo apt install --only-upgrade linux-image-generic (or the installed flavour: linux-image-aws, -azure, -gcp, -virtual)

sudo dnf upgrade --refresh kernel

sudo dnf upgrade --refresh kernel

sudo zypper refresh
sudo zypper update kernel-default

sudo dnf upgrade --releasever=latest kernel kernel6.12

sudo pacman -Syu

apk update && apk upgrade linux-lts linux-virt

not Linux

General update steps for every system are on the Linux and Unix & BSD pages; after updating, see which services to restart.

Fix status in Linux distributions

From the Debian security tracker, Ubuntu CVE tracker and Red Hat Security Data API, refreshed every few hours.

Sources

• https://git.kernel.org/stable/c/828938118d6c2bb711301748c3e39e4bed6a62f5
• https://git.kernel.org/stable/c/057dac23d329d5c5ed62352f2659a39fd46c6d4a
• CVE-2026-98163 on CVE.org
• CVE-2026-98163 on NVD

Page generated automatically from official sources on 2026-11-03 18:05 UTC. Always confirm with your vendor's advisory.