Vulnerability-Lookup

GHSA-XHVW-VPQW-3XGX

Vulnerability from github – Published: 2026-08-27 06:31 – Updated: 2026-08-27 06:31

Details

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

mptcp: fastopen: only mark MPTFO subflows with SYN data

Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty.

mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established().

Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty.

Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO".

Severity

9.4 (Critical)


                  
                    CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H

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{
  "affected": [],
  "aliases": [
    "CVE-2026-80585"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-26T15:17:14Z",
    "severity": "CRITICAL"
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fastopen: only mark MPTFO subflows with SYN data\n\nPassive TCP Fast Open accepts a valid-cookie SYN even when it carries\nno data. In that case the child socket\u0027s receive queue is intentionally\nleft empty.\n\nmptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking\nfor queued SYN data. That made data-less TFO SYNs hit a WARN and, if\nthe warning was non-fatal, left stale MPTFO state behind. The stale\nflag could later trigger a state-confusion bug in\ncheck_fully_established().\n\nOnly mark the subflow as MPTFO after confirming that an SKB was queued.\nReturn quietly when the receive queue is empty.\n\nNote that mptcp_subflow_context\u0027s is_mptfo field is now not just about\nsubflows where the TFO was present, but about MPTFO subflow that\nconsumed SYN data. Only having a valid cookie but not carrying data is\nnot really \"doing TFO\".",
  "id": "GHSA-xhvw-vpqw-3xgx",
  "modified": "2026-08-27T06:31:33Z",
  "published": "2026-08-27T06:31:33Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-80585"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H",
      "type": "CVSS_V3"
    }
  ]
}

CVE-2026-80585 (GCVE-0-2026-80585)

Vulnerability from cvelistv5 – Published: 2026-08-26 14:37 – Updated: 2026-08-27 05:02

Title

mptcp: fastopen: only mark MPTFO subflows with SYN data

Summary

In the Linux kernel, the following vulnerability has been resolved: mptcp: fastopen: only mark MPTFO subflows with SYN data Passive TCP Fast Open accepts a valid-cookie SYN even when it carries no data. In that case the child socket's receive queue is intentionally left empty. mptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking for queued SYN data. That made data-less TFO SYNs hit a WARN and, if the warning was non-fatal, left stale MPTFO state behind. The stale flag could later trigger a state-confusion bug in check_fully_established(). Only mark the subflow as MPTFO after confirming that an SKB was queued. Return quietly when the receive queue is empty. Note that mptcp_subflow_context's is_mptfo field is now not just about subflows where the TFO was present, but about MPTFO subflow that consumed SYN data. Only having a valid cookie but not carrying data is not really "doing TFO".

Severity

9.4 (Critical)


                        
                          CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H

Assigner

Linux mitre root

References

5 references

URL	Tags
https://git.kernel.org/stable/c/f75f174edc8657385…
https://git.kernel.org/stable/c/fca7e444c04689fe4…
https://git.kernel.org/stable/c/75e564b2ced1cc3d9…
https://git.kernel.org/stable/c/72b4a0c51a4b550d4…
https://git.kernel.org/stable/c/e00b63056fb4f2614…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: 36b122baf6a8bd46b4a591f12f4ed17b22257408 , < f75f174edc865738522e514d042cf5627f084859 (git) Affected: 36b122baf6a8bd46b4a591f12f4ed17b22257408 , < fca7e444c04689fe4cc6b56f2725f804a4bb1ef9 (git) Affected: 36b122baf6a8bd46b4a591f12f4ed17b22257408 , < 75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5 (git) Affected: 36b122baf6a8bd46b4a591f12f4ed17b22257408 , < 72b4a0c51a4b550d40301d60a366b429b8c8e78d (git) Affected: 36b122baf6a8bd46b4a591f12f4ed17b22257408 , < e00b63056fb4f261455b3e5df5268a1f8ce47a87 (git)
Linux	Linux	Affected: 6.2 Unaffected: 0 , < 6.2 (semver) Unaffected: 6.6.153 , ≤ 6.6.* (semver) Unaffected: 6.12.105 , ≤ 6.12.* (semver) Unaffected: 6.18.46 , ≤ 6.18.* (semver) Unaffected: 7.1.10 , ≤ 7.1.* (semver) Unaffected: 7.2 , ≤ * (original_commit_for_fix)

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/fastopen.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "f75f174edc865738522e514d042cf5627f084859",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
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              "status": "affected",
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              "versionType": "git"
            },
            {
              "lessThan": "75e564b2ced1cc3d9a8904c7d2d2bb448fffb8b5",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "72b4a0c51a4b550d40301d60a366b429b8c8e78d",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            },
            {
              "lessThan": "e00b63056fb4f261455b3e5df5268a1f8ce47a87",
              "status": "affected",
              "version": "36b122baf6a8bd46b4a591f12f4ed17b22257408",
              "versionType": "git"
            }
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        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
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          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
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              "version": "6.2"
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            {
              "lessThan": "6.2",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
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            {
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              "status": "unaffected",
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              "versionType": "semver"
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            {
              "lessThanOrEqual": "6.12.*",
              "status": "unaffected",
              "version": "6.12.105",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "6.18.*",
              "status": "unaffected",
              "version": "6.18.46",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.10",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "*",
              "status": "unaffected",
              "version": "7.2",
              "versionType": "original_commit_for_fix"
            }
          ]
        }
      ],
      "cpeApplicability": [
        {
          "nodes": [
            {
              "cpeMatch": [
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.6.153",
                  "versionStartIncluding": "6.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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                  "versionStartIncluding": "6.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "6.18.46",
                  "versionStartIncluding": "6.2",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.1.10",
                  "versionStartIncluding": "6.2",
                  "vulnerable": true
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                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
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              "negate": false,
              "operator": "OR"
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fastopen: only mark MPTFO subflows with SYN data\n\nPassive TCP Fast Open accepts a valid-cookie SYN even when it carries\nno data. In that case the child socket\u0027s receive queue is intentionally\nleft empty.\n\nmptcp_fastopen_subflow_synack_set_params() set is_mptfo before checking\nfor queued SYN data. That made data-less TFO SYNs hit a WARN and, if\nthe warning was non-fatal, left stale MPTFO state behind. The stale\nflag could later trigger a state-confusion bug in\ncheck_fully_established().\n\nOnly mark the subflow as MPTFO after confirming that an SKB was queued.\nReturn quietly when the receive queue is empty.\n\nNote that mptcp_subflow_context\u0027s is_mptfo field is now not just about\nsubflows where the TFO was present, but about MPTFO subflow that\nconsumed SYN data. Only having a valid cookie but not carrying data is\nnot really \"doing TFO\"."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.4,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is reached by sending crafted TCP/MPTCP segments to a listening socket over the network (ip4/ip6 receive -\u003e tcp_conn_request/tcp_rcv_state_process -\u003e subflow_prep_synack or mptcp_incoming_options -\u003e check_fully_established); per kernel CNA guidance, net stack packet-handling paths are Network.\nAC:L - In the intended passive-MPTFO deployment (MPTCP listener with net.ipv4.tcp_fastopen server bit set), the attacker controls obtaining a valid TFO cookie and then sending a data-less SYN followed by an out-of-order MPC_ACK to deterministically hit the stale is_mptfo path in check_fully_established().\nPR:N - Exploitation requires only unauthenticated inbound TCP connections to an MPTCP listener; the attacker obtains the TFO cookie from their own prior connection and needs no local account, capability, or namespace privileges on the target host.\nUI:N - No victim interaction is required beyond the server normally accepting TCP connections; the attacker programmatically sends the SYN and follow-up MPC_ACK packets without anyone opening files, clicking links, or performing other actions.\nS:U - Impact is confined to kernel MPTCP/TCP connection state on the target host and does not cross VM, container, IOMMU, or other security boundaries; it is not a sandbox or guest-to-host escape.\nC:L - Premature fully_established with attacker-chosen MPTCP keys desynchronizes handshake and DSS/map state, enabling misdelivery or premature exposure of connection-level data/metadata to the remote peer before normal MP_CAPABLE validation completes.\nI:H - Stale is_mptfo lets an out-of-order MPC_ACK force __mptcp_subflow_fully_established(), writing attacker-controlled sndr_key/ack_seq into msk and subflow crypto state and corrupting subsequent DSS/ACK handling on the server multipath socket.\nA:H - Data-less passive-TFO SYNs hit WARN_ON_ONCE(!skb) on every trigger, and the resulting inconsistent is_mptfo/fully_established state can cause repeatable kernel WARN/oops (panic_on_warn panic) plus connection reset storms against internet-facing MPTCP servers."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-27T05:02:06.112Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/f75f174edc865738522e514d042cf5627f084859"
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          "url": "https://git.kernel.org/stable/c/fca7e444c04689fe4cc6b56f2725f804a4bb1ef9"
        },
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        },
        {
          "url": "https://git.kernel.org/stable/c/72b4a0c51a4b550d40301d60a366b429b8c8e78d"
        },
        {
          "url": "https://git.kernel.org/stable/c/e00b63056fb4f261455b3e5df5268a1f8ce47a87"
        }
      ],
      "title": "mptcp: fastopen: only mark MPTFO subflows with SYN data",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-80585",
    "datePublished": "2026-08-26T14:37:40.901Z",
    "dateReserved": "2026-08-26T14:34:25.769Z",
    "dateUpdated": "2026-08-27T05:02:06.112Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

Detection rules are retrieved from Rulezet.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.

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GHSA-XHVW-VPQW-3XGX

CVE-2026-80585 (GCVE-0-2026-80585)

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Sightings

Nomenclature