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CVE-2025-38415

Estado: AnalizadaAlta (7.8)—

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

Squashfs: check return result of sb_min_blocksize

Syzkaller reports an "UBSAN: shift-out-of-bounds in squashfs_bio_read" bug.

Syzkaller forks multiple processes which after mounting the Squashfs filesystem, issues an ioctl("/dev/loop0", LOOP_SET_BLOCK_SIZE, 0x8000). Now if this ioctl occurs at the same time another process is in the process of mounting a Squashfs filesystem on /dev/loop0, the failure occurs. When this happens the following code in squashfs_fill_super() fails.

sb_min_blocksize() returns 0, which means msblk->devblksize is set to 0.

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As a result, ffz(~msblk->devblksize) returns 64, and msblk->devblksize_log2 is set to 64.

This subsequently causes the

UBSAN: shift-out-of-bounds in fs/squashfs/block.c:195:36 shift exponent 64 is too large for 64-bit type 'u64' (aka 'unsigned long long')

This commit adds a check for a 0 return by sb_min_blocksize().

Detalles técnicos trazas, registros y código del informe original
----
msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE);
msblk->devblksize_log2 = ffz(~msblk->devblksize);
----

CVSS

Probabilidad de explotación (EPSS)

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.

Acceso local sin interacción del usuario (AV:L, PR:L, UI:N) permite escalar privilegios mediante race condition en montaje de Squashfs, causando DoS por shift-out-of-bounds que bloquea el 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

Threat Intelligence ProgramFilter Network TrafficExecution PreventionApplication Isolation and SandboxingExploit ProtectionUpdate Software

Tecnologías afectadas (2)

Debian — Debian LinuxLinux — Linux Kernel

CWE

Referencias

JSON original (NVD)

Mostrar
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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nSquashfs: check return result of sb_min_blocksize\n\nSyzkaller reports an \"UBSAN: shift-out-of-bounds in squashfs_bio_read\" bug.\n\nSyzkaller forks multiple processes which after mounting the Squashfs\nfilesystem, issues an ioctl(\"/dev/loop0\", LOOP_SET_BLOCK_SIZE, 0x8000). \nNow if this ioctl occurs at the same time another process is in the\nprocess of mounting a Squashfs filesystem on /dev/loop0, the failure\noccurs.  When this happens the following code in squashfs_fill_super()\nfails.\n\n----\nmsblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE);\nmsblk->devblksize_log2 = ffz(~msblk->devblksize);\n----\n\nsb_min_blocksize() returns 0, which means msblk->devblksize is set to 0.\n\nAs a result, ffz(~msblk->devblksize) returns 64, and msblk->devblksize_log2\nis set to 64.\n\nThis subsequently causes the\n\nUBSAN: shift-out-of-bounds in fs/squashfs/block.c:195:36\nshift exponent 64 is too large for 64-bit type 'u64' (aka\n'unsigned long long')\n\nThis commit adds a check for a 0 return by sb_min_blocksize()."
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    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: Squashfs: comprobar el resultado devuelto de sb_min_blocksize. Syzkaller informa del error \"UBSAN: desplazamiento fuera de los límites en squashfs_bio_read\". Syzkaller bifurca varios procesos que, tras montar el sistema de archivos Squashfs, emiten una instrucción ioctl(\"/dev/loop0\", LOOP_SET_BLOCK_SIZE, 0x8000). Si esta instrucción ioctl se produce al mismo tiempo que otro proceso está montando un sistema de archivos Squashfs en /dev/loop0, se produce el fallo. En este caso, el siguiente código en squashfs_fill_super() falla: ---- msblk->devblksize = sb_min_blocksize(sb, SQUASHFS_DEVBLK_SIZE); msblk->devblksize_log2 = ffz(~msblk->devblksize); ---- sb_min_blocksize() devuelve 0, lo que significa que msblk->devblksize está establecido en 0. Como resultado, ffz(~msblk->devblksize) devuelve 64 y msblk->devblksize_log2 está establecido en 64. Esto posteriormente provoca el UBSAN: shift-out-of-bounds en fs/squashfs/block.c:195:36 el exponente de desplazamiento 64 es demasiado grande para el tipo de 64 bits 'u64' (también conocido como 'unsigned long long') Esta confirmación agrega una comprobación para un retorno de 0 por sb_min_blocksize()."
    }
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