CVE-2026-80587

Estado: RecibidaCrítica (9.8)—

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

mptcp: avoid combining some incoming suboptions

Some MPTCP suboptions are mutually exclusive according to the RFC8684, but also because in different places, the code doesn't expect some combinations to be present. That's specially true for suboptions that would be present twice, but with different attributes.

The new restrictions are the same as the ones applied on the output side, with mptcp_write_options. The same rules can be reused with a small fix: an MP_FASTCLOSE can be used with a DSS when the sender picks this option [1], which is not the case on Linux. Here are the rules:

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The only difference is with the 'P': another stack could send and ADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be allowed.

A few points of attention:

Detalles técnicos trazas, registros y código del informe original

  Which options can be used together?

  X: mutually exclusive
  O: often used together
  C: can be used together in some cases
  P: could be used together but we prefer not to (optimisations)

  | Opt: | MPC  | MPJ  | DSS  | ADD  |  RM  | PRIO | FAIL |  FC  |
  |------|------|------|------|------|------|------|------|------|
  | MPC  |------|------|------|------|------|------|------|------|
  | MPJ  |  X   |------|------|------|------|------|------|------|
  | DSS  |  X   |  X   |------|------|------|------|------|------|
  | ADD  |  X   |  X   |  P   |------|------|------|------|------|
  | RM   |  C   |  C   |  C   |  P   |------|------|------|------|
  | PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|
  | FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|
  | FC   |  X   |  X   |  P   |  X   |  X   |  X   |  X   |------|
  | RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |
  |------|------|------|------|------|------|------|------|------|

 - In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is
   no reason to add it with a SYN. Note that even with a 4th ACK, it
   doesn't seem to be useful, except when IDs are known in advance via
   another channel. Better not to break that.

 - Now, combining both an MP_CAPABLE and an MP_JOIN will no longer
   result to a reject of the two options, but only the second suboption
   is ignored. That seems OK to do that for this unexpected error. At
   least now all inconsistent combinations are handled the same way.
   This could change later in next. This also means the explicit checks
   for having both MPC + MPJ in subflow.c will now be unreachable.
   That's fine, they will be removed in a follow-up patch.

 - In case of conflicting combinations, the extra suboption(s) is/are
   ignored: having such combinations either means the remote peer is
   buggy, or is evil. The simplest action is then taken in this case:
   stop processing the current suboption.

 - In mp_opt->suboptions, there is also a bit reserved to the checksum,
   which can be used in an MP_CAPABLE and a DSS. Each time a DSS option
   can be used in parallel with another option, the checksum can be set,
   so the verification is combined into a new OPTIONS_MPTCP_DSS macro.

 - An MP_CAPABLE ACK can carry a Data-Level Length, and an optional
   Checksum: they are the same as the ones found in a DSS, because a DSS
   cannot be used in parallel to an MP_CAPABLE. Similarly, even if there
   is room, a DSS cannot be used with an MP_JOIN.

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: 0.40%
Percentil entre todas las CVEs puntuadas: 32
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 access85 %

Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N indica red sin autenticación; vulnerable MPTCP parse en kernel permite código remoto vía subopciones malformadas, potencial DoS por procesamiento anómalo.

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

Vulnerability Scanning Privileged Account Management Network Segmentation Limit Access to Resource Over Network Filter Network Traffic 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-2026-80587",
  "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",
          "availabilityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "confidentialityImpact": "HIGH"
        },
        "impactScore": 5.9,
        "exploitabilityScore": 3.9
      }
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    {
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
      "affectedData": [
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          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "product": "Linux",
          "versions": [
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          "programFiles": [
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            "net/mptcp/protocol.h"
          ],
          "defaultStatus": "unaffected"
        },
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            {
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              "version": "0",
              "lessThan": "5.6",
              "versionType": "semver"
            },
            {
              "status": "unaffected",
              "version": "5.15.218",
              "versionType": "semver",
              "lessThanOrEqual": "5.15.*"
            },
            {
              "status": "unaffected",
              "version": "6.6.153",
              "versionType": "semver",
              "lessThanOrEqual": "6.6.*"
            },
            {
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              "version": "6.12.105",
              "versionType": "semver",
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              "version": "7.2",
              "versionType": "original_commit_for_fix",
              "lessThanOrEqual": "*"
            }
          ],
          "programFiles": [
            "net/mptcp/options.c",
            "net/mptcp/protocol.h"
          ],
          "defaultStatus": "affected"
        }
      ]
    }
  ],
  "published": "2026-08-26T15:17:15.017",
  "references": [
    {
      "url": "https://git.kernel.org/stable/c/099bfcbd0c16ae9b50aba2a1bea033e63f895da7",
      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
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      "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
    }
  ],
  "vulnStatus": "Received",
  "descriptions": [
    {
      "lang": "en",
      "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: avoid combining some incoming suboptions\n\nSome MPTCP suboptions are mutually exclusive according to the RFC8684,\nbut also because in different places, the code doesn't expect some\ncombinations to be present. That's specially true for suboptions that\nwould be present twice, but with different attributes.\n\nThe new restrictions are the same as the ones applied on the output\nside, with mptcp_write_options. The same rules can be reused with a\nsmall fix: an MP_FASTCLOSE can be used with a DSS when the sender picks\nthis option [1], which is not the case on Linux. Here are the rules:\n\n  Which options can be used together?\n\n  X: mutually exclusive\n  O: often used together\n  C: can be used together in some cases\n  P: could be used together but we prefer not to (optimisations)\n\n  | Opt: | MPC  | MPJ  | DSS  | ADD  |  RM  | PRIO | FAIL |  FC  |\n  |------|------|------|------|------|------|------|------|------|\n  | MPC  |------|------|------|------|------|------|------|------|\n  | MPJ  |  X   |------|------|------|------|------|------|------|\n  | DSS  |  X   |  X   |------|------|------|------|------|------|\n  | ADD  |  X   |  X   |  P   |------|------|------|------|------|\n  | RM   |  C   |  C   |  C   |  P   |------|------|------|------|\n  | PRIO |  X   |  C   |  C   |  C   |  C   |------|------|------|\n  | FAIL |  X   |  X   |  C   |  X   |  X   |  X   |------|------|\n  | FC   |  X   |  X   |  P   |  X   |  X   |  X   |  X   |------|\n  | RST  |  X   |  X   |  X   |  X   |  X   |  X   |  O   |  O   |\n  |------|------|------|------|------|------|------|------|------|\n\nThe only difference is with the 'P': another stack could send and\nADD_ADDR with other suboptions (DSS, RM_ADDR), and this should be\nallowed.\n\nA few points of attention:\n\n - In theory, an MP_CAPABLE could be used with a RM_ADDR, but there is\n   no reason to add it with a SYN. Note that even with a 4th ACK, it\n   doesn't seem to be useful, except when IDs are known in advance via\n   another channel. Better not to break that.\n\n - Now, combining both an MP_CAPABLE and an MP_JOIN will no longer\n   result to a reject of the two options, but only the second suboption\n   is ignored. That seems OK to do that for this unexpected error. At\n   least now all inconsistent combinations are handled the same way.\n   This could change later in next. This also means the explicit checks\n   for having both MPC + MPJ in subflow.c will now be unreachable.\n   That's fine, they will be removed in a follow-up patch.\n\n - In case of conflicting combinations, the extra suboption(s) is/are\n   ignored: having such combinations either means the remote peer is\n   buggy, or is evil. The simplest action is then taken in this case:\n   stop processing the current suboption.\n\n - In mp_opt->suboptions, there is also a bit reserved to the checksum,\n   which can be used in an MP_CAPABLE and a DSS. Each time a DSS option\n   can be used in parallel with another option, the checksum can be set,\n   so the verification is combined into a new OPTIONS_MPTCP_DSS macro.\n\n - An MP_CAPABLE ACK can carry a Data-Level Length, and an optional\n   Checksum: they are the same as the ones found in a DSS, because a DSS\n   cannot be used in parallel to an MP_CAPABLE. Similarly, even if there\n   is room, a DSS cannot be used with an MP_JOIN."
    }
  ],
  "lastModified": "2026-08-27T13:18:41.093",
  "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"
}