Vulnerability-Lookup

CVE-2026-68170 (GCVE-0-2026-68170)

Vulnerability from cvelistv5 – Published: 2026-08-10 11:59 – Updated: 2026-08-10 11:59

Title

mptcp: fix stale skb->sk reference on subflow close

Summary

In the Linux kernel, the following vulnerability has been resolved: mptcp: fix stale skb->sk reference on subflow close The backlog list is updated by mptcp_data_ready() under mptcp_data_lock(). The cleanup of backlog references to a closing subflow, however, was performed in mptcp_close_ssk(), before __mptcp_close_ssk() acquires the ssk lock, and while holding neither the ssk lock nor mptcp_data_lock(). Because that traversal ran without mptcp_data_lock(), concurrent softirq RX processing on another CPU (subflow_data_ready() -> mptcp_data_ready() -> __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog entry referencing the ssk while the cleanup loop was in progress. Such an entry could be missed by the cleanup, or the concurrent list update could corrupt the traversal, leaving skb->sk pointing at the ssk after it is freed. A later mptcp_backlog_purge() then dereferences the stale pointer, triggering a warning in inet_sock_destruct() (ssk->sk_rmem_alloc != 0) followed by a use-after-free in mptcp_backlog_purge(). Fix this by moving the backlog cleanup into __mptcp_close_ssk(), after subflow->closing is set to 1 and while the ssk lock is still held, serialized under mptcp_data_lock(). The cleanup runs only on the push path (MPTCP_CF_PUSH), where backlog references accumulate; on other teardown paths the caller already handles cleanup. With subflow->closing set and mptcp_data_lock() held across the purge, any concurrent mptcp_data_ready() either completes its enqueue before the purge runs and is caught, or observes closing=1 and bails out. Once mptcp_data_unlock() is reached, no new skb referencing the ssk can be enqueued, so the cleanup is exhaustive. Remove the unprotected traversal from mptcp_close_ssk() entirely.

Severity

No CVSS data available.

Assigner

Linux

References

2 references

URL	Tags
https://git.kernel.org/stable/c/625fc6060864889fe…
https://git.kernel.org/stable/c/bd7aae448f6ee9d82…

Impacted products

2 products

Vendor	Product	Version
Linux	Linux	Affected: ee458a3f314e9c669ddd227bf5ab08354d9e75cc , < 625fc6060864889fe3d370cdeffbbab762af3cb4 (git) Affected: ee458a3f314e9c669ddd227bf5ab08354d9e75cc , < bd7aae448f6ee9d82599a4474664de1e6e91a535 (git)
Linux	Linux	Affected: 6.19 Unaffected: 0 , < 6.19 (semver) Unaffected: 7.1.6 , ≤ 7.1.* (semver) Unaffected: 7.2-rc5 , ≤ * (original_commit_for_fix)

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{
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        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/protocol.c"
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      "cpeApplicability": [
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        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-10T11:59:39.174Z",
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        "shortName": "Linux"
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          "url": "https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4"
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        {
          "url": "https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535"
        }
      ],
      "title": "mptcp: fix stale skb-\u003esk reference on subflow close",
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    "datePublished": "2026-08-10T11:59:39.174Z",
    "dateReserved": "2026-07-30T09:28:09.372Z",
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    "state": "PUBLISHED"
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    "epss": {
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      "date": "2026-08-11",
      "epss": "0.00189",
      "percentile": "0.08794"
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    "redhat_vex": {
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      "cve": "CVE-2026-68170",
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      "product_status:known_not_affected": "276",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: Linux kernel MPTCP: Use-after-free vulnerability",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68170.json",
      "version": "3"
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}

GHSA-385R-J2F8-HQW6

Vulnerability from github – Published: 2026-08-10 15:33 – Updated: 2026-08-10 15:33

Details

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

mptcp: fix stale skb->sk reference on subflow close

The backlog list is updated by mptcp_data_ready() under mptcp_data_lock(). The cleanup of backlog references to a closing subflow, however, was performed in mptcp_close_ssk(), before __mptcp_close_ssk() acquires the ssk lock, and while holding neither the ssk lock nor mptcp_data_lock().

Because that traversal ran without mptcp_data_lock(), concurrent softirq RX processing on another CPU (subflow_data_ready() -> mptcp_data_ready() -> __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog entry referencing the ssk while the cleanup loop was in progress. Such an entry could be missed by the cleanup, or the concurrent list update could corrupt the traversal, leaving skb->sk pointing at the ssk after it is freed.

A later mptcp_backlog_purge() then dereferences the stale pointer, triggering a warning in inet_sock_destruct() (ssk->sk_rmem_alloc != 0) followed by a use-after-free in mptcp_backlog_purge().

Fix this by moving the backlog cleanup into __mptcp_close_ssk(), after subflow->closing is set to 1 and while the ssk lock is still held, serialized under mptcp_data_lock(). The cleanup runs only on the push path (MPTCP_CF_PUSH), where backlog references accumulate; on other teardown paths the caller already handles cleanup.

With subflow->closing set and mptcp_data_lock() held across the purge, any concurrent mptcp_data_ready() either completes its enqueue before the purge runs and is caught, or observes closing=1 and bails out. Once mptcp_data_unlock() is reached, no new skb referencing the ssk can be enqueued, so the cleanup is exhaustive.

Remove the unprotected traversal from mptcp_close_ssk() entirely.

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-68170"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-10T13:20:03Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\nmptcp: fix stale skb-\u003esk reference on subflow close\n\nThe backlog list is updated by mptcp_data_ready() under\nmptcp_data_lock(). The cleanup of backlog references to a closing\nsubflow, however, was performed in mptcp_close_ssk(), before\n__mptcp_close_ssk() acquires the ssk lock, and while holding neither\nthe ssk lock nor mptcp_data_lock().\n\nBecause that traversal ran without mptcp_data_lock(), concurrent softirq\nRX processing on another CPU (subflow_data_ready() -\u003e mptcp_data_ready()\n-\u003e __mptcp_add_backlog(), under mptcp_data_lock()) could add a backlog\nentry referencing the ssk while the cleanup loop was in progress. Such\nan entry could be missed by the cleanup, or the concurrent list update\ncould corrupt the traversal, leaving skb-\u003esk pointing at the ssk after\nit is freed.\n\nA later mptcp_backlog_purge() then dereferences the stale pointer,\ntriggering a warning in inet_sock_destruct() (ssk-\u003esk_rmem_alloc != 0)\nfollowed by a use-after-free in mptcp_backlog_purge().\n\nFix this by moving the backlog cleanup into __mptcp_close_ssk(), after\nsubflow-\u003eclosing is set to 1 and while the ssk lock is still held,\nserialized under mptcp_data_lock(). The cleanup runs only on the push\npath (MPTCP_CF_PUSH), where backlog references accumulate; on other\nteardown paths the caller already handles cleanup.\n\nWith subflow-\u003eclosing set and mptcp_data_lock() held across the purge,\nany concurrent mptcp_data_ready() either completes its enqueue before\nthe purge runs and is caught, or observes closing=1 and bails out. Once\nmptcp_data_unlock() is reached, no new skb referencing the ssk can be\nenqueued, so the cleanup is exhaustive.\n\nRemove the unprotected traversal from mptcp_close_ssk() entirely.",
  "id": "GHSA-385r-j2f8-hqw6",
  "modified": "2026-08-10T15:33:39Z",
  "published": "2026-08-10T15:33:39Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-68170"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

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.

Action not permitted

CVE-2026-68170 (GCVE-0-2026-68170)

GHSA-385R-J2F8-HQW6

Tags

Sightings

Nomenclature