CVE-2026-43050
Estado: AnalizadaAlta (7)—
In the Linux kernel, the following vulnerability has been resolved:
atm: lec: fix use-after-free in sock_def_readable()
A race condition exists between lec_atm_close() setting priv->lecd to NULL and concurrent access to priv->lecd in send_to_lecd(), lec_handle_bridge(), and lec_atm_send(). When the socket is freed via RCU while another thread is still using it, a use-after-free occurs in sock_def_readable() when accessing the socket's wait queue.
The root cause is that lec_atm_close() clears priv->lecd without any synchronization, while callers dereference priv->lecd without any protection against concurrent teardown.
Detalles técnicos trazas, registros y código del informe original
Fix this by converting priv->lecd to an RCU-protected pointer:
- Mark priv->lecd as __rcu in lec.h
- Use rcu_assign_pointer() in lec_atm_close() and lecd_attach()
for safe pointer assignment
- Use rcu_access_pointer() for NULL checks that do not dereference
the pointer in lec_start_xmit(), lec_push(), send_to_lecd() and
lecd_attach()
- Use rcu_read_lock/rcu_dereference/rcu_read_unlock in send_to_lecd(),
lec_handle_bridge() and lec_atm_send() to safely access lecd
- Use rcu_assign_pointer() followed by synchronize_rcu() in
lec_atm_close() to ensure all readers have completed before
proceeding. This is safe since lec_atm_close() is called from
vcc_release() which holds lock_sock(), a sleeping lock.
- Remove the manual sk_receive_queue drain from lec_atm_close()
since vcc_destroy_socket() already drains it after lec_atm_close()
returns.
v2: Switch from spinlock + sock_hold/put approach to RCU to properly
fix the race. The v1 spinlock approach had two issues pointed out
by Eric Dumazet:
1. priv->lecd was still accessed directly after releasing the
lock instead of using a local copy.
2. The spinlock did not prevent packets being queued after
lec_atm_close() drains sk_receive_queue since timer and
workqueue paths bypass netif_stop_queue().
Note: Syzbot patch testing was attempted but the test VM terminated
unexpectedly with "Connection to localhost closed by remote host",
likely due to a QEMU AHCI emulation issue unrelated to this fix.
Compile testing with "make W=1 net/atm/lec.o" passes cleanly.CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 7
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.16%
- Percentil entre todas las CVEs puntuadas: 4
- Fecha de la puntuación: 5/10/2026
EPSS (Exploit Prediction Scoring System, de FIRST) estima la probabilidad de que una vulnerabilidad sea explotada en 30 días. Complementa a CVSS (impacto) y a CISA KEV (explotación confirmada).
🎯 Técnicas ATT&CK
Cómo se explota esta vulnerabilidad y qué consigue el atacante, en el lenguaje de MITRE ATT&CK.
- Explotación
T1068Exploitation for Privilege Escalationprivilege escalation85 % - Impacto principal
T1059Command and Scripting Interpreterexecution75 %
Acceso local (AV:L) con privilegios (PR:L) sin interacción del usuario; la race condition permite ejecutar código en el contexto del núcleo. CWE-416 (use-after-free) típicamente permite ejecución arbitraria tras ganar acceso al kernel.
Inferido por nuestro agente de análisis a partir de la descripción oficial, el vector CVSS y la CWE, y comprobado por un supervisor. Puede contener errores.
🛡️ Mitigaciones ATT&CK que cubren estas técnicas
Tecnologías afectadas (1)
CWE
- CWE-416
Referencias
- https://git.kernel.org/stable/c/317843d5355062020649124eb4a0d7acbcc3f53e
- https://git.kernel.org/stable/c/3989740fa4978e1d2d51ecc62be1b01093e104ad
- https://git.kernel.org/stable/c/3e8b25f32f2f35549d03d77da030a24a45bdef5b
- https://git.kernel.org/stable/c/5fbbb1ff936d7ff9528d929c1549977e8123d8a8
- https://git.kernel.org/stable/c/750a33f417f3d196b86375f8d9f8938bacf130fe
- https://git.kernel.org/stable/c/922814879542c2e397b0e9641fd36b8202a8e555
- https://git.kernel.org/stable/c/abc10f85a3965ac14b9ed7ad3e67b35604a63aa3
- https://git.kernel.org/stable/c/b256d055da47258e63f8b40965f276c5f23d229a
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\natm: lec: fix use-after-free in sock_def_readable()\n\nA race condition exists between lec_atm_close() setting priv->lecd\nto NULL and concurrent access to priv->lecd in send_to_lecd(),\nlec_handle_bridge(), and lec_atm_send(). When the socket is freed\nvia RCU while another thread is still using it, a use-after-free\noccurs in sock_def_readable() when accessing the socket's wait queue.\n\nThe root cause is that lec_atm_close() clears priv->lecd without\nany synchronization, while callers dereference priv->lecd without\nany protection against concurrent teardown.\n\nFix this by converting priv->lecd to an RCU-protected pointer:\n- Mark priv->lecd as __rcu in lec.h\n- Use rcu_assign_pointer() in lec_atm_close() and lecd_attach()\n for safe pointer assignment\n- Use rcu_access_pointer() for NULL checks that do not dereference\n the pointer in lec_start_xmit(), lec_push(), send_to_lecd() and\n lecd_attach()\n- Use rcu_read_lock/rcu_dereference/rcu_read_unlock in send_to_lecd(),\n lec_handle_bridge() and lec_atm_send() to safely access lecd\n- Use rcu_assign_pointer() followed by synchronize_rcu() in\n lec_atm_close() to ensure all readers have completed before\n proceeding. This is safe since lec_atm_close() is called from\n vcc_release() which holds lock_sock(), a sleeping lock.\n- Remove the manual sk_receive_queue drain from lec_atm_close()\n since vcc_destroy_socket() already drains it after lec_atm_close()\n returns.\n\nv2: Switch from spinlock + sock_hold/put approach to RCU to properly\n fix the race. The v1 spinlock approach had two issues pointed out\n by Eric Dumazet:\n 1. priv->lecd was still accessed directly after releasing the\n lock instead of using a local copy.\n 2. The spinlock did not prevent packets being queued after\n lec_atm_close() drains sk_receive_queue since timer and\n workqueue paths bypass netif_stop_queue().\n\nNote: Syzbot patch testing was attempted but the test VM terminated\n unexpectedly with \"Connection to localhost closed by remote host\",\n likely due to a QEMU AHCI emulation issue unrelated to this fix.\n Compile testing with \"make W=1 net/atm/lec.o\" passes cleanly."
}
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