CVE-2026-63951

Estado: Pendiente de análisisAlta (7.8)—

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

zram: fix use-after-free in zram_writeback_endio

A crash was observed in zram_writeback_endio due to a NULL pointer dereference in wake_up. The root cause is a race condition between the bio completion handler (zram_writeback_endio) and the writeback task.

In zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after releasing wb_ctl->done_lock. This creates a race window where the writeback task can see num_inflight become 0, return, and free wb_ctl before zram_writeback_endio calls wake_up().

This patch fixes this race by using RCU. By protecting wb_ctl with rcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it, we ensure that wb_ctl remains valid during the execution of zram_writeback_endio.

Detalles técnicos trazas, registros y código del informe original

CPU 0 (zram_writeback_endio)     CPU 1 (writeback_store)
============================     ============================
                                 zram_writeback_slots
                                   zram_submit_wb_request
                                   zram_submit_wb_request
                                   wait_event(wb_ctl->done_wait)
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
wake_up(&wb_ctl->done_wait);
                                   zram_complete_done_reqs
spin_lock(&wb_ctl->done_lock);
list_add(&req->entry, &wb_ctl->done_reqs);
spin_unlock(&wb_ctl->done_lock);
                                   while (num_inflight) > 0)
                                     spin_lock(&wb_ctl->done_lock);
                                     list_del(&req->entry);
                                     spin_unlock(&wb_ctl->done_lock);
                                     // num_inflight becomes 0
                                     atomic_dec(num_inflight);

                                 // Leave zram_writeback_slots
                                 // Free wb_ctl
                                 release_wb_ctl(wb_ctl);
// UAF crash!
wake_up(&wb_ctl->done_wait);

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: 0.18%
Percentil entre todas las CVEs puntuadas: 7
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.

ExplotaciónT1068 Exploitation for Privilege Escalationprivilege escalation85 %
Impacto principalT1499.004 Application or System Exploitationimpact75 %

Vulnerabilidad local de race condition en zram que causa crash por use-after-free (AV:L, PR:L). Impacto de DoS por pánico del kernel. Requiere acceso local con 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

Threat Intelligence Program Filter Network Traffic Execution Prevention Application Isolation and Sandboxing Exploit Protection Update Software

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)

Mostrar

{
  "id": "CVE-2026-63951",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Secondary",
        "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.8,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H",
          "integrityImpact": "HIGH",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 1.8
      }
    ]
  },
  "affected": [
    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "f405066a1f0db818270f49a5e96be329bcabde1e",
              "lessThan": "ebe2cbefc86291fa7f386447a81995640df4e2fd",
              "versionType": "git"
            },
            {
              "status": "affected",
              "version": "f405066a1f0db818270f49a5e96be329bcabde1e",
              "lessThan": "bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43",
              "versionType": "git"
            }
          ],
          "programFiles": [
            "drivers/block/zram/zram_drv.c"
          ],
          "defaultStatus": "unaffected"
        },
        {
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "status": "unaffected",
              "version": "0",
              "lessThan": "6.19",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "7.0.12",
              "versionType": "semver",
              "lessThanOrEqual": "7.0.*"
            },
            {
              "status": "unaffected",
              "version": "7.1",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "drivers/block/zram/zram_drv.c"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-07-19T16:17:13.837",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/bf62f69574b19720ae5fbbbcdf24a0c4e3e05e43",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    },
    {
      "url": "https://git.kernel.org/stable/c/ebe2cbefc86291fa7f386447a81995640df4e2fd",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Awaiting Analysis",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nzram: fix use-after-free in zram_writeback_endio\n\nA crash was observed in zram_writeback_endio due to a NULL pointer\ndereference in wake_up.  The root cause is a race condition between the\nbio completion handler (zram_writeback_endio) and the writeback task.\n\nIn zram_writeback_endio, wake_up() is called on &wb_ctl->done_wait after\nreleasing wb_ctl->done_lock.  This creates a race window where the\nwriteback task can see num_inflight become 0, return, and free wb_ctl\nbefore zram_writeback_endio calls wake_up().\n\nCPU 0 (zram_writeback_endio)     CPU 1 (writeback_store)\n============================     ============================\n                                 zram_writeback_slots\n                                   zram_submit_wb_request\n                                   zram_submit_wb_request\n                                   wait_event(wb_ctl->done_wait)\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\nwake_up(&wb_ctl->done_wait);\n                                   zram_complete_done_reqs\nspin_lock(&wb_ctl->done_lock);\nlist_add(&req->entry, &wb_ctl->done_reqs);\nspin_unlock(&wb_ctl->done_lock);\n                                   while (num_inflight) > 0)\n                                     spin_lock(&wb_ctl->done_lock);\n                                     list_del(&req->entry);\n                                     spin_unlock(&wb_ctl->done_lock);\n                                     // num_inflight becomes 0\n                                     atomic_dec(num_inflight);\n\n                                 // Leave zram_writeback_slots\n                                 // Free wb_ctl\n                                 release_wb_ctl(wb_ctl);\n// UAF crash!\nwake_up(&wb_ctl->done_wait);\n\nThis patch fixes this race by using RCU.  By protecting wb_ctl with\nrcu_read_lock() in zram_writeback_endio and using kfree_rcu() to free it,\nwe ensure that wb_ctl remains valid during the execution of\nzram_writeback_endio."
    }
  ],
  "lastModified": "2026-07-27T17:44:23.777",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}