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)

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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-2026-98163)

Note that Nessus relies on the presence of the package as reported by the vendor.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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-2026-98163)

ID	Name	Product	Family	Type	Severity
376443	Ubuntu 24.04 LTS / 26.04 LTS : Linux kernel vulnerabilities (USN-8959-1)	Nessus	Ubuntu Local Security Checks	Local	high
369312	Linux Distros Unpatched Vulnerability : CVE-2026-98163	Nessus	Misc.	Local	high
474754	Chainguard: multiple linux-desktop-7.2 packages: security update to 7.2.11-r0	Tenable Cloud Security	Chainguard Local Security Checks	Local	high
474754	Chainguard: multiple linux-desktop-7.2 packages: security update to 7.2.11-r0	Tenable Self-Hosted Container Security	Chainguard Local Security Checks	Local	high

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