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

  - signal: Prevent exec() race Hyunwoo debugged the following KASAN UAF splat: BUG: KASAN: slab-use-after-     free in __send_signal_locked+0xb27/0xba0 Write of size 8 at addr ffff888007ed80c8 by task poc/79 ... Call     Trace: __send_signal_locked+0xb27/0xba0 do_send_sig_info+0xa7/0x160 do_send_specific+0x76/0xa0
    __x64_sys_tgkill+0x193/0x270 ... Allocated by task 80: do_timer_create+0x1a4/0x1030
    __x64_sys_timer_create+0x145/0x190 ... Freed by task 12: kmem_cache_free_bulk+0x1f8/0x4a0     kvfree_rcu_bulk+0x14f/0x1c0 kfree_rcu_work+0x128/0x1a0 ... Last potentially related work creation:
    kvfree_call_rcu+0x39/0x390 __flush_itimer_signals+0x211/0x320 flush_itimer_signals+0x47/0x90     begin_new_exec+0xa6b/0x28c0 It turned out that this happens with a non-leader exec() as Hyunwoo explained:
    de_thread() calls exchange_tids() before release_task(leader), so the struct pid held by a SIGEV_THREAD_ID     timer created against the leader's tid now points to the thread which called execve(). pid_task() returns     that thread and lock_task_sighand() on it succeeds. If the timer signal is blocked, its sigqueue stays     queued on the leader's task::pending. The next expiry of that timer can then run while release_task()     flushes the queue. posixtimer_send_sigqueue() checks whether the sigqueue is already queued with a plain     list_empty(), which only reads list_head::next. list_del_init() is not atomic and INIT_LIST_HEAD() stores     list_head::next before list_head::prev, so the check can pass in between. list_add_tail() queues the entry     on the task::pending of the live thread, and the list_head::prev store from the flush then overwrites the     list_head::prev link that list_add_tail() has just set. __flush_itimer_signals() does not undo that     either. With list_head::prev pointing at the entry itself, its list_del_init() only stores the same values     again, so the entry is not removed from the list. It is still there after the last reference is dropped     and the timer is freed by RCU, and the list_add_tail() of a later tgkill() follows that list_head::prev     into the freed timer. This problem surfaced with the recent commit which moved the sigqueue flush out of     the sighand lock held region. Hyonwoo proposed to fix this by using list_del_init_careful(), but that just     papers over the problem. After some disucssions and various attempts to solve it, Eric pointed out that     there is no reason to flush task::pending late in release_task() and it should be done in exit_signals()     already. As nothing can collect and deliver signals which are queued in a dying task's pending queue,     there is no reason to delay it further. But it has to be ensured that no signals can be queued into it     after that point. exit_signals() sets PF_EXITING in task::flags, which can be used as an indicator for     this. Cure it by: - Preventing signal queueing for task private signals (PIDTYPE_PID) when the task has     PF_EXITING set in __send_signal_locked() and in posixtimer_send_sigqueue(). - Protecting the unlocked     setting of PF_EXITING in exit_signals() for the task group empty and the group exit case with sighand lock
    - Flushing task::pending signals right there. Optimize that by moving the whole pending list to an on-     stack list head under sighand lock and free the signals without the lock held. There has been quite some     discussion about the lockless flush and the non-leader exec case on weakly ordered systems. The problem is     that a third party which tries to send a posix timer signal relies on the PID lookup to find the target     task and that lookup might result in the new leader when the signal was originaly directed to the old     leader. In case that the signal was queued on the old leader then the lockless flush raised a concern over     the following situation: old_leader new_leader third party A: flush_list() // list_del_in ---truncated---     (CVE-2026-98256)

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

Detections

Analytics

Linux Distros Unpatched Vulnerability : CVE-2026-98256

high Nessus Plugin ID 364267

Version 1.6