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CVE-2022-49961

Estado: ModificadaAlta (7.1)—

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

bpf: Do mark_chain_precision for ARG_CONST_ALLOC_SIZE_OR_ZERO

Precision markers need to be propagated whenever we have an ARG_CONST_* style argument, as the verifier cannot consider imprecise scalars to be equivalent for the purposes of states_equal check when such arguments refine the return value (in this case, set mem_size for PTR_TO_MEM).

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The resultant mem_size for the R0 is derived from the constant value, and if the verifier incorrectly prunes states considering them equivalent where such arguments exist (by seeing that both registers have reg->precise as false in regsafe), we can end up with invalid programs passing the verifier which can do access beyond what should have been the correct mem_size in that explored state.

To show a concrete example of the problem:

For the first case, the single line execution's exploration will prune the search at insn 14 for the branch insn 9's second leg as it will be verified first using r2 = -1 (UINT_MAX), while as w1 at insn 9 will always be 0 so at runtime we don't get error for being greater than UINT_MAX/4 from bpf_ringbuf_reserve. The verifier during regsafe just sees reg->precise as false for both r2 registers in both states, hence considers them equal for purposes of states_equal.

If we propagated precise markers using the backtracking support, we would use the precise marking to then ensure that old r2 (UINT_MAX) was within the new r2 (1) and this would never be true, so the verification would rightfully fail.

The end result is that the out of bounds access at instruction 19 would be permitted without this fix.

Note that reg->precise is always set to true when user does not have CAP_BPF (or when subprog count is greater than 1 (i.e. use of any static or global functions)), hence this is only a problem when precision marks need to be explicitly propagated (i.e. privileged users with CAP_BPF).

A simplified test case has been included in the next patch to prevent future regressions.

Detalles técnicos trazas, registros y código del informe original
0000000000000000 <prog>:
       0:       r2 = *(u32 *)(r1 + 80)
       1:       r1 = *(u32 *)(r1 + 76)
       2:       r3 = r1
       3:       r3 += 4
       4:       if r3 > r2 goto +18 <LBB5_5>
       5:       w2 = 0
       6:       *(u32 *)(r1 + 0) = r2
       7:       r1 = *(u32 *)(r1 + 0)
       8:       r2 = 1
       9:       if w1 == 0 goto +1 <LBB5_3>
      10:       r2 = -1

0000000000000058 <LBB5_3>:
      11:       r1 = 0 ll
      13:       r3 = 0
      14:       call bpf_ringbuf_reserve
      15:       if r0 == 0 goto +7 <LBB5_5>
      16:       r1 = r0
      17:       r1 += 16777215
      18:       w2 = 0
      19:       *(u8 *)(r1 + 0) = r2
      20:       r1 = r0
      21:       r2 = 0
      22:       call bpf_ringbuf_submit

00000000000000b8 <LBB5_5>:
      23:       w0 = 0
      24:       exit

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.

AV:L, PR:L indica escalada local; el bypass del verificador eBPF permite ejecución de código no validado y acceso a memoria fuera de límites en programas eBPF privilegiados (CAP_BPF).

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

Execution PreventionThreat Intelligence ProgramRestrict Web-Based ContentPrivileged Account ManagementLimit Software InstallationBehavior Prevention on Endpoint

Tecnologías afectadas (1)

Linux — Linux Kernel

CWE

Referencias

JSON original (NVD)

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{
  "id": "CVE-2022-49961",
  "cveTags": [],
  "metrics": {
    "cvssMetricV31": [
      {
        "type": "Primary",
        "source": "nvd@nist.gov",
        "cvssData": {
          "scope": "UNCHANGED",
          "version": "3.1",
          "baseScore": 7.1,
          "attackVector": "LOCAL",
          "baseSeverity": "HIGH",
          "vectorString": "CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H",
          "integrityImpact": "NONE",
          "userInteraction": "NONE",
          "attackComplexity": "LOW",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "LOW",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.2,
        "exploitabilityScore": 1.8
      }
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
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          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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              "version": "0",
              "lessThan": "5.8",
              "versionType": "semver"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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  "weaknesses": [
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      "type": "Primary",
      "source": "nvd@nist.gov",
      "description": [
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          "value": "CWE-125"
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      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nbpf: Do mark_chain_precision for ARG_CONST_ALLOC_SIZE_OR_ZERO\n\nPrecision markers need to be propagated whenever we have an ARG_CONST_*\nstyle argument, as the verifier cannot consider imprecise scalars to be\nequivalent for the purposes of states_equal check when such arguments\nrefine the return value (in this case, set mem_size for PTR_TO_MEM). The\nresultant mem_size for the R0 is derived from the constant value, and if\nthe verifier incorrectly prunes states considering them equivalent where\nsuch arguments exist (by seeing that both registers have reg->precise as\nfalse in regsafe), we can end up with invalid programs passing the\nverifier which can do access beyond what should have been the correct\nmem_size in that explored state.\n\nTo show a concrete example of the problem:\n\n0000000000000000 <prog>:\n       0:       r2 = *(u32 *)(r1 + 80)\n       1:       r1 = *(u32 *)(r1 + 76)\n       2:       r3 = r1\n       3:       r3 += 4\n       4:       if r3 > r2 goto +18 <LBB5_5>\n       5:       w2 = 0\n       6:       *(u32 *)(r1 + 0) = r2\n       7:       r1 = *(u32 *)(r1 + 0)\n       8:       r2 = 1\n       9:       if w1 == 0 goto +1 <LBB5_3>\n      10:       r2 = -1\n\n0000000000000058 <LBB5_3>:\n      11:       r1 = 0 ll\n      13:       r3 = 0\n      14:       call bpf_ringbuf_reserve\n      15:       if r0 == 0 goto +7 <LBB5_5>\n      16:       r1 = r0\n      17:       r1 += 16777215\n      18:       w2 = 0\n      19:       *(u8 *)(r1 + 0) = r2\n      20:       r1 = r0\n      21:       r2 = 0\n      22:       call bpf_ringbuf_submit\n\n00000000000000b8 <LBB5_5>:\n      23:       w0 = 0\n      24:       exit\n\nFor the first case, the single line execution's exploration will prune\nthe search at insn 14 for the branch insn 9's second leg as it will be\nverified first using r2 = -1 (UINT_MAX), while as w1 at insn 9 will\nalways be 0 so at runtime we don't get error for being greater than\nUINT_MAX/4 from bpf_ringbuf_reserve. The verifier during regsafe just\nsees reg->precise as false for both r2 registers in both states, hence\nconsiders them equal for purposes of states_equal.\n\nIf we propagated precise markers using the backtracking support, we\nwould use the precise marking to then ensure that old r2 (UINT_MAX) was\nwithin the new r2 (1) and this would never be true, so the verification\nwould rightfully fail.\n\nThe end result is that the out of bounds access at instruction 19 would\nbe permitted without this fix.\n\nNote that reg->precise is always set to true when user does not have\nCAP_BPF (or when subprog count is greater than 1 (i.e. use of any static\nor global functions)), hence this is only a problem when precision marks\nneed to be explicitly propagated (i.e. privileged users with CAP_BPF).\n\nA simplified test case has been included in the next patch to prevent\nfuture regressions."
    },
    {
      "lang": "es",
      "value": "En el kernel de Linux, se ha resuelto la siguiente vulnerabilidad: bpf: Hacer mark_chain_precision para ARG_CONST_ALLOC_SIZE_OR_ZERO Los marcadores de precisión deben propagarse siempre que tengamos un argumento de estilo ARG_CONST_*, ya que el verificador no puede considerar que los escalares imprecisos sean equivalentes para los fines de la comprobación states_equal cuando dichos argumentos refinan el valor de retorno (en este caso, establecer mem_size para PTR_TO_MEM). El mem_size resultante para el R0 se deriva del valor constante, y si el verificador poda incorrectamente los estados considerándolos equivalentes donde existen dichos argumentos (al ver que ambos registros tienen reg-&gt;precise como falso en regsafe), podemos terminar con programas no válidos que pasan el verificador que pueden hacer acceso más allá de lo que debería haber sido el mem_size correcto en ese estado explorado. Para mostrar un ejemplo concreto del problema: 0000000000000000 : 0: r2 = *(u32 *)(r1 + 80) 1: r1 = *(u32 *)(r1 + 76) 2: r3 = r1 3: r3 += 4 4: si r3 &gt; r2 goto +18  5: w2 = 0 6: *(u32 *)(r1 + 0) = r2 7: r1 = *(u32 *)(r1 + 0) 8: r2 = 1 9: si w1 == 0 goto +1  10: r2 = -1 0000000000000058 : 11: r1 = 0 ll 13: r3 = 0 14: llamar a bpf_ringbuf_reserve 15: si r0 == 0 goto +7  16: r1 = r0 17: r1 += 16777215 18: w2 = 0 19: *(u8 *)(r1 + 0) = r2 20: r1 = r0 21: r2 = 0 22: llamar a bpf_ringbuf_submit 00000000000000b8 : 23: w0 = 0 24: salir Para el primer caso, la exploración de la ejecución de una sola línea podará la búsqueda en insn 14 para la segunda rama de la rama insn 9, ya que se verificará primero utilizando r2 = -1 (UINT_MAX), mientras que como w1 en insn 9 siempre será 0, por lo que en tiempo de ejecución no obtenemos un error por ser mayor que UINT_MAX/4 de bpf_ringbuf_reserve. El verificador durante regsafe solo ve reg-&gt;precise como falso para ambos registros r2 en ambos estados, por lo tanto, los considera iguales para fines de states_equal. Si propagáramos marcadores precisos utilizando el soporte de retroceso, usaríamos el marcado preciso para asegurarnos de que el antiguo r2 (UINT_MAX) estuviera dentro del nuevo r2 (1) y esto nunca sería verdadero, por lo que la verificación fallaría legítimamente. El resultado final es que el acceso fuera de los límites en la instrucción 19 se permitiría sin esta corrección. Tenga en cuenta que reg-&gt;precise siempre se establece en verdadero cuando el usuario no tiene CAP_BPF (o cuando el recuento de subprocesos es mayor que 1 (es decir, uso de cualquier función estática o global)), por lo tanto, esto solo es un problema cuando las marcas de precisión deben propagarse explícitamente (es decir, usuarios privilegiados con CAP_BPF). Se ha incluido un caso de prueba simplificado en el próximo parche para evitar futuras regresiones."
    }
  ],
  "lastModified": "2026-06-17T05:19:37.817",
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