CVE-2026-52991
In the Linux kernel, the following vulnerability has been resolved:
sched/psi: fix race between file release and pressure write
A potential race condition exists between pressure write and cgroup file release regarding the priv member of struct kernfs_open_file, which triggers the uaf reported in [1].
Consider the following scenario involving execution on two separate CPUs:
CPU0 CPU1 ==== ==== vfs_rmdir() kernfs_iop_rmdir() cgroup_rmdir() cgroup_kn_lock_live() cgroup_destroy_locked() cgroup_addrm_files() cgroup_rm_file() kernfs_remove_by_name() kernfs_remove_by_name_ns() vfs_write() __kernfs_remove() new_sync_write() kernfs_drain() kernfs_fop_write_iter() kernfs_drain_open_files() cgroup_file_write() kernfs_release_file() pressure_write() cgroup_file_release() ctx = of->priv; kfree(ctx); of->priv = NULL; cgroup_kn_unlock() cgroup_kn_lock_live() cgroup_get(cgrp) cgroup_kn_unlock() if (ctx->psi.trigger) // here, trigger uaf for ctx, that is of->priv
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The cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards the memory deallocation of of->priv performed within cgroup_file_release(). However, the operations involving of->priv executed within pressure_write() are not entirely covered by the protection of cgroup_mutex. Consequently, if the code in pressure_write(), specifically the section handling the ctx variable executes after cgroup_file_release() has completed, a uaf vulnerability involving of->priv is triggered.
Therefore, the issue can be resolved by extending the scope of the cgroup_mutex lock within pressure_write() to encompass all code paths involving of->priv, thereby properly synchronizing the race condition occurring between cgroup_file_release() and pressure_write().
And, if an live kn lock can be successfully acquired while executing the pressure write operation, it indicates that the cgroup deletion process has not yet reached its final stage; consequently, the priv pointer within open_file cannot be NULL. Therefore, the operation to retrieve the ctx value must be moved to a point *after* the live kn lock has been successfully acquired.
In another situation, specifically after entering cgroup_kn_lock_live() but before acquiring cgroup_mutex, there exists a different class of race condition:
CPU0: write memory.pressure CPU1: write cgroup.pressure=0 =========================== =============================
cgroup_pressure_write() cgroup_kn_lock_live(cgroup.pressure) cgroup_file_show(memory.pressure, false) kernfs_show(false) kernfs_drain_open_files() cgroup_file_release(of) kfree(ctx) of->priv = NULL cgroup_kn_unlock()
Consequently, there is a possibility that of->priv is NULL, the pressure write needs to check for this.
Now that the scope of the cgroup_mutex has been expanded, the original explicit cgroup_get/put operations are no longer necessary, this is because acquiring/releasing the live kn lock inherently executes a cgroup get/put operation.
Detalles técnicos trazas, registros y código del informe original
kernfs_fop_write_iter()
kernfs_get_active_of(of)
pressure_write()
cgroup_kn_lock_live(memory.pressure)
cgroup_tryget(cgrp)
kernfs_break_active_protection(kn)
... blocks on cgroup_mutex
... acquires cgroup_mutex
ctx = of->priv; // may now be NULL
if (ctx->psi.trigger) // NULL dereference
[1]
BUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
Call Trace:
pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011
cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:43
---truncated---CVSS
- Versión: 3.1
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- Puntuación base: 7.8
Probabilidad de explotación (EPSS)
- Probabilidad de explotación en los próximos 30 días: 0.11%
- Percentil entre todas las CVEs puntuadas: 1
- 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 escalation75 %
Race condition en cgroup_mutex (CWE-362/367) con acceso local (AV:L, PR:L) permite escalada local vía use-after-free. Kernel Linux vulnerable.
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-362
- CWE-367
Referencias
- https://git.kernel.org/stable/c/03dc070fa0fc3cb4068693f468ccd5f8a7e58282
- https://git.kernel.org/stable/c/a5b98009f16d8a5fb4a8ff9a193f5735515c38fa
- https://git.kernel.org/stable/c/d4352c0709bfd38c752fccbde7fd72a82ac78f23
- https://access.redhat.com/errata/RHSA-2026:57251
- https://access.redhat.com/errata/RHSA-2026:57252
- https://access.redhat.com/errata/RHSA-2026:57253
- https://access.redhat.com/errata/RHSA-2026:57254
- https://access.redhat.com/security/cve/CVE-2026-52991
- https://bugzilla.redhat.com/show_bug.cgi?id=2492403
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52991.json
JSON original (NVD)
Mostrar
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"value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsched/psi: fix race between file release and pressure write\n\nA potential race condition exists between pressure write and cgroup file\nrelease regarding the priv member of struct kernfs_open_file, which\ntriggers the uaf reported in [1].\n\nConsider the following scenario involving execution on two separate CPUs:\n\n CPU0\t\t\t\t\tCPU1\n ====\t\t\t\t\t====\n\t\t\t\t\tvfs_rmdir()\n\t\t\t\t\tkernfs_iop_rmdir()\n\t\t\t\t\tcgroup_rmdir()\n\t\t\t\t\tcgroup_kn_lock_live()\n\t\t\t\t\tcgroup_destroy_locked()\n\t\t\t\t\tcgroup_addrm_files()\n\t\t\t\t\tcgroup_rm_file()\n\t\t\t\t\tkernfs_remove_by_name()\n\t\t\t\t\tkernfs_remove_by_name_ns()\n vfs_write()\t\t\t\t__kernfs_remove()\n new_sync_write()\t\t\tkernfs_drain()\n kernfs_fop_write_iter()\t\tkernfs_drain_open_files()\n cgroup_file_write()\t\t\tkernfs_release_file()\n pressure_write()\t\t\tcgroup_file_release()\n ctx = of->priv;\n\t\t\t\t\tkfree(ctx);\n \t\t\t\t\tof->priv = NULL;\n\t\t\t\t\tcgroup_kn_unlock()\n cgroup_kn_lock_live()\n cgroup_get(cgrp)\n cgroup_kn_unlock()\n if (ctx->psi.trigger) // here, trigger uaf for ctx, that is of->priv\n\nThe cgroup_rmdir() is protected by the cgroup_mutex, it also safeguards\nthe memory deallocation of of->priv performed within cgroup_file_release().\nHowever, the operations involving of->priv executed within pressure_write()\nare not entirely covered by the protection of cgroup_mutex. Consequently,\nif the code in pressure_write(), specifically the section handling the\nctx variable executes after cgroup_file_release() has completed, a uaf\nvulnerability involving of->priv is triggered.\n\nTherefore, the issue can be resolved by extending the scope of the\ncgroup_mutex lock within pressure_write() to encompass all code paths\ninvolving of->priv, thereby properly synchronizing the race condition\noccurring between cgroup_file_release() and pressure_write().\n\nAnd, if an live kn lock can be successfully acquired while executing\nthe pressure write operation, it indicates that the cgroup deletion\nprocess has not yet reached its final stage; consequently, the priv\npointer within open_file cannot be NULL. Therefore, the operation to\nretrieve the ctx value must be moved to a point *after* the live kn\nlock has been successfully acquired.\n\nIn another situation, specifically after entering cgroup_kn_lock_live()\nbut before acquiring cgroup_mutex, there exists a different class of\nrace condition:\n\nCPU0: write memory.pressure CPU1: write cgroup.pressure=0\n===========================\t\t =============================\n\nkernfs_fop_write_iter()\n kernfs_get_active_of(of)\n pressure_write()\n cgroup_kn_lock_live(memory.pressure)\n cgroup_tryget(cgrp)\n kernfs_break_active_protection(kn)\n ... blocks on cgroup_mutex\n\n \t cgroup_pressure_write()\n \t cgroup_kn_lock_live(cgroup.pressure)\n \t cgroup_file_show(memory.pressure, false)\n \t kernfs_show(false)\n \t kernfs_drain_open_files()\n \t cgroup_file_release(of)\n \t kfree(ctx)\n \t of->priv = NULL\n \t cgroup_kn_unlock()\n\n ... acquires cgroup_mutex\n ctx = of->priv; // may now be NULL\n if (ctx->psi.trigger) // NULL dereference\n\nConsequently, there is a possibility that of->priv is NULL, the pressure\nwrite needs to check for this.\n\nNow that the scope of the cgroup_mutex has been expanded, the original\nexplicit cgroup_get/put operations are no longer necessary, this is\nbecause acquiring/releasing the live kn lock inherently executes a\ncgroup get/put operation.\n\n[1]\nBUG: KASAN: slab-use-after-free in pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011\nCall Trace:\n pressure_write+0xa4/0x210 kernel/cgroup/cgroup.c:4011\n cgroup_file_write+0x36f/0x790 kernel/cgroup/cgroup.c:43\n---truncated---"
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"lastModified": "2026-08-20T13:19:00.250",
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