CVE-2026-98256 Condición de carrera en exec() que provoca uso después de liberar en el kernel Linux

Qué es CVE-2026-98256

Se detectó un uso después de liberar en __send_signal_locked durante un exec() no líder, ya que de_thread() llama a exchange_tids() antes de tiempo. La corrección previene esta condición de carrera en exec().

Productos y versiones afectadas

• Linux

  • desde fb3bbcfe344e64a46574a638b051ffd78762c12d hasta antes de 621c365739828900f32a0c1cdfe5387528a62176
  • desde fb3bbcfe344e64a46574a638b051ffd78762c12d hasta antes de 934bd95f1a6404dbb845951b823547abab05a649
  • desde fb3bbcfe344e64a46574a638b051ffd78762c12d hasta antes de d2710c8d938ae6a825a6463158e6e6f31eac792a

• Linux

  • 6.15

Qué hacer

1. Verificá si usás Linux y en qué versión: el rango afectado figura arriba.
2. Actualizá a la versión corregida que indique el fabricante en su aviso (ver referencias) o aplicá la mitigación que publique.
3. Priorizá la corrección: hay código de explotación público, así que el riesgo de ataque es alto.
4. Revisá registros y accesos de los sistemas expuestos para descartar que se haya aprovechado antes de corregir.

Exploits y pruebas de concepto públicas

Código publicado por terceros. Puede ser malicioso: revisalo solo en un entorno aislado.

• ylh440104/InfinityCore-Android-CVE-2026-98256 ↗Android/ARM64 portPUBLICADO 19 OCT · 04:59

Calculadora CVSS

CVSS 3.1 · 7.8 ALTA

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

VECTOR DE ATAQUE (AV)

Local

COMPLEJIDAD DEL ATAQUE (AC)

Baja

PRIVILEGIOS REQUERIDOS (PR)

Bajos

INTERACCIÓN DEL USUARIO (UI)

Ninguna

ALCANCE (S)

Sin cambio

CONFIDENCIALIDAD (C)

Alta

INTEGRIDAD (I)

Alta

DISPONIBILIDAD (A)

Alta

Abrir la calculadora completa →

Descripción original

In the Linux kernel, the following vulnerability has been resolved: 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---

Referencias

• git.kernel.org/stable/c/621c365739828900f32a0c1cdfe5387528a62176
• git.kernel.org/stable/c/934bd95f1a6404dbb845951b823547abab05a649
• git.kernel.org/stable/c/d2710c8d938ae6a825a6463158e6e6f31eac792a

Historial de la alerta

1. 19 OCT · 04:59EXPLOIT PÚBLICO Se publicó el repositorio ylh440104/InfinityCore-Android-CVE-2026-98256.

CÓMO SE HIZOResumen traducido automáticamente al español a partir de la descripción original. Ante dudas, la descripción original y las referencias del fabricante son la fuente de verdad. Cómo funciona.