CVE-2026-72422

Estado: RecibidaCrítica (9.8)—

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

ksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE

conn->preauth_info is shared connection state (struct preauth_integrity_info, kmalloc-96) that is allocated and freed by the SMB2 NEGOTIATE handler and read by the response send path.

smb2_handle_negotiate() allocates conn->preauth_info, and on a deassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the allocation and the free/NULL happen under ksmbd_conn_lock(conn) (the connection srv_mutex), which is held across the whole handler body.

The response send path smb3_preauth_hash_rsp(), called from the send: block of __handle_ksmbd_work(), reads conn->preauth_info and dereferences conn->preauth_info->Preauth_HashValue (via ksmbd_gen_preauth_integrity_hash()) without taking conn_lock.

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When a client drives two SMB2 NEGOTIATE requests on the same connection, one worker can free conn->preauth_info on the failing-negotiate path while a concurrent send-path worker is reading it, producing a slab use-after-free read (KASAN-confirmed).

The send-path read tested conn->preauth_info for NULL but raced with the free that occurs between the NULL check and the dereference, so the NULL guard alone does not close the window.

Serialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under ksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock. Because the negotiate handler holds conn_lock across its kfree + NULL assignment, a reader that also takes conn_lock either runs fully before the allocation or fully after the NULL store, and can never observe the freed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash() takes no locks itself (it only computes a SHA-512 over the buffer), so no lock-ordering inversion is introduced, and conn_lock is a sleepable mutex which is safe on this send path (it already performs network I/O).

CVSS

Versión: 3.1
Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Puntuación base: 9.8

Probabilidad de explotación (EPSS)

Probabilidad de explotación en los próximos 30 días: 0.72%
Percentil entre todas las CVEs puntuadas: 52
Fecha de la puntuación: 6/10/2026

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.

ExplotaciónT1190 Exploit Public-Facing Applicationinitial access75 %
Impacto principalT1499.004 Application or System Exploitationimpact70 %

Vulnerabilidad de uso-después-liberación en ksmbd (servidor SMB2 en kernel Linux) explotable remotamente sin autenticación (AV:N, PR:N, UI:N). El atacante puede causar DoS por crash del kernel o leer memoria del kernel adyacente, potencialmente elevando privilegios.

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

Filter Network Traffic Vulnerability Scanning Privileged Account Management Network Segmentation Limit Access to Resource Over Network Application Isolation and Sandboxing

Tecnologías afectadas (1)

⚠ Inferidas por IA a partir de la descripción — NVD aún no ha analizado esta CVE; no son CPE verificados.

Linux — Linux Kernel^AI

Referencias

JSON original (NVD)

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{
  "id": "CVE-2026-72422",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 9.8,
          "attackVector": "NETWORK",
          "baseSeverity": "CRITICAL",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
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  "published": "2026-08-15T06:22:15.987",
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  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nksmbd: fix use-after-free of conn->preauth_info in concurrent SMB2 NEGOTIATE\n\nconn->preauth_info is shared connection state (struct\npreauth_integrity_info, kmalloc-96) that is allocated and freed by the\nSMB2 NEGOTIATE handler and read by the response send path.\n\nsmb2_handle_negotiate() allocates conn->preauth_info, and on a\ndeassemble_neg_contexts() failure kfrees it and sets it to NULL. Both the\nallocation and the free/NULL happen under ksmbd_conn_lock(conn) (the\nconnection srv_mutex), which is held across the whole handler body.\n\nThe response send path smb3_preauth_hash_rsp(), called from the send:\nblock of __handle_ksmbd_work(), reads conn->preauth_info and dereferences\nconn->preauth_info->Preauth_HashValue (via\nksmbd_gen_preauth_integrity_hash()) without taking conn_lock. When a\nclient drives two SMB2 NEGOTIATE requests on the same connection, one\nworker can free conn->preauth_info on the failing-negotiate path while a\nconcurrent send-path worker is reading it, producing a slab\nuse-after-free read (KASAN-confirmed).\n\nThe send-path read tested conn->preauth_info for NULL but raced with the\nfree that occurs between the NULL check and the dereference, so the NULL\nguard alone does not close the window.\n\nSerialize the NEGOTIATE-branch read in smb3_preauth_hash_rsp() under\nksmbd_conn_lock(conn) and re-check conn->preauth_info inside the lock.\nBecause the negotiate handler holds conn_lock across its kfree + NULL\nassignment, a reader that also takes conn_lock either runs fully before\nthe allocation or fully after the NULL store, and can never observe the\nfreed-but-not-yet-NULLed pointer. ksmbd_gen_preauth_integrity_hash()\ntakes no locks itself (it only computes a SHA-512 over the buffer), so\nno lock-ordering inversion is introduced, and conn_lock is a sleepable\nmutex which is safe on this send path (it already performs network I/O)."
    }
  ],
  "lastModified": "2026-08-17T06:19:09.393",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}