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CVE-2026-53360

Estado: AnalizadaAlta (8.8)—

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

KVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use

As per the GHCB spec, when using GHCB v2+ require the software scratch area to reside in the GHCB's shared buffer. Note, things like Page State Change (PSC) requests _rely_ on this behavior, as the guest can't provide a length when making the request, i.e. the size of the guest payload is bounded by the size of the shared buffer.

Failure to force usage of the GHCB, and a slew of other flaws, lets a malicious SNP guest corrupt host kernel heap memory, and leak host heap layout information.

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setup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2), where exit_info_2 is guest-controlled. With exit_info_2=24, this yields a 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer holds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only entries[0] and entries[1] are in-bounds.

snp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253) but NOT against the actual buffer size:

The guest sets end_entry=10+, causing the host to iterate entries[2+] which are OOB into adjacent slab objects. For each OOB entry:

The guest controls allocation size (exit_info_2), entry range (cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly hit different slab positions.

E.g. with KASAN enabled, a single insmod of the PoC guest module produces 73 KASAN reports:

All credit to Stan for the wonderful description and reproducer!

[sean: write changelog]

Detalles técnicos trazas, registros y código del informe original
      idx_end = hdr->end_entry;

      if (idx_end >= VMGEXIT_PSC_MAX_COUNT) {   // checks 253, not buffer
          snp_complete_psc(svm, ...);
          return 1;
      }

      for (idx = idx_start; idx <= idx_end; idx++) {
          entry_start = entries[idx];           // OOB when idx >= 2

  - The host reads 8 bytes (OOB READ / info leak oracle)
  - If the data passes PSC validation, __snp_complete_one_psc() writes
    cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806)
  - If validation fails, the error response reveals whether adjacent
    memory is zero vs non-zero (information disclosure to guest)

By exploiting the variety of bugs, a malicious SEV-SNP guest can:
    - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure)
    - OOB write cur_page bits into adjacent objects (heap corruption)
    - Trigger use-after-free conditions across VMGEXITs

    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890
    Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199

    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890
    Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199

    The buggy address belongs to the object at ffff888XXXXXXXXX
     which belongs to the cache kmalloc-cg-32 of size 32
    The buggy address is located N bytes to the right of
     allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX)

  Breakdown:
    62 slab-out-of-bounds (reads + writes past allocation)
     7 slab-use-after-free
     4 use-after-free

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.

Vulnerabilidad de escalada de privilegios local (AV:L, PR:L) en KVM/SEV que permite a huésped SNP malicioso leer y corromper memoria del kernel anfitrión mediante lecturas OOB y escrituras en objetos slab adyacentes.

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 ProgramRestrict File and Directory PermissionsRemote Data StorageExecution PreventionEncrypt Sensitive InformationApplication Isolation and Sandboxing

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nKVM: SEV: Require in-GHCB scratch area if GHCB v2+ is in use\n\nAs per the GHCB spec, when using GHCB v2+ require the software scratch area\nto reside in the GHCB's shared buffer.  Note, things like Page State Change\n(PSC) requests _rely_ on this behavior, as the guest can't provide a length\nwhen making the request, i.e. the size of the guest payload is bounded by\nthe size of the shared buffer.\n\nFailure to force usage of the GHCB, and a slew of other flaws, lets a\nmalicious SNP guest corrupt host kernel heap memory, and leak host heap\nlayout information.\n\nsetup_vmgexit_scratch() allocates a buffer via kvzalloc(exit_info_2),\nwhere exit_info_2 is guest-controlled. With exit_info_2=24, this yields\na 24-byte allocation in kmalloc-cg-32 (32-byte slab objects). The buffer\nholds an 8-byte psc_hdr followed by 8-byte psc_entry structs, so only\nentries[0] and entries[1] are in-bounds.\n\nsnp_begin_psc() validates end_entry against VMGEXIT_PSC_MAX_COUNT (253)\nbut NOT against the actual buffer size:\n\n      idx_end = hdr->end_entry;\n\n      if (idx_end >= VMGEXIT_PSC_MAX_COUNT) {   // checks 253, not buffer\n          snp_complete_psc(svm, ...);\n          return 1;\n      }\n\n      for (idx = idx_start; idx <= idx_end; idx++) {\n          entry_start = entries[idx];           // OOB when idx >= 2\n\nThe guest sets end_entry=10+, causing the host to iterate entries[2+]\nwhich are OOB into adjacent slab objects. For each OOB entry:\n\n  - The host reads 8 bytes (OOB READ / info leak oracle)\n  - If the data passes PSC validation, __snp_complete_one_psc() writes\n    cur_page = 1 or 512 into the entry (OOB WRITE, sev.c:3806)\n  - If validation fails, the error response reveals whether adjacent\n    memory is zero vs non-zero (information disclosure to guest)\n\nThe guest controls allocation size (exit_info_2), entry range\n(cur_entry/end_entry), and can fire unlimited VMGEXITs to repeatedly\nhit different slab positions.\n\nBy exploiting the variety of bugs, a malicious SEV-SNP guest can:\n    - OOB read adjacent kmalloc-cg-32 objects (heap layout disclosure)\n    - OOB write cur_page bits into adjacent objects (heap corruption)\n    - Trigger use-after-free conditions across VMGEXITs\n\nE.g. with KASAN enabled, a single insmod of the PoC guest module\nproduces 73 KASAN reports:\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x126/0x890\n    Read of size 8 at addr ffff888219ffb5e0 by task qemu-system-x86/2199\n\n    BUG: KASAN: slab-out-of-bounds in snp_begin_psc+0x468/0x890\n    Write of size 8 at addr ffff888351566648 by task qemu-system-x86/2199\n\n    The buggy address belongs to the object at ffff888XXXXXXXXX\n     which belongs to the cache kmalloc-cg-32 of size 32\n    The buggy address is located N bytes to the right of\n     allocated 32-byte region [ffff888XXXXXXXXX, ffff888XXXXXXXXX)\n\n  Breakdown:\n    62 slab-out-of-bounds (reads + writes past allocation)\n     7 slab-use-after-free\n     4 use-after-free\n\nAll credit to Stan for the wonderful description and reproducer!\n\n[sean: write changelog]"
    }
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