GCVE Workshop - 22 September 2026 (14:00-18:00), Luxembourg Before The Vulnopticon Conference - Registration

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

Vulnerability from cvelistv5 – Published: 2026-08-10 11:59 – Updated: 2026-08-17 05:00
VLAI
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
9.8 (Critical)
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: ee458a3f314e9c669ddd227bf5ab08354d9e75cc , < 625fc6060864889fe3d370cdeffbbab762af3cb4 (git)
Affected: ee458a3f314e9c669ddd227bf5ab08354d9e75cc , < bd7aae448f6ee9d82599a4474664de1e6e91a535 (git)
guessed Create a notification for this product.
Linux Linux Affected: 6.19
Unaffected: 0 , < 6.19 (semver)
Unaffected: 7.1.6 , ≤ 7.1.* (semver)
Unaffected: 7.2 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
Show details on NVD website
To clipboard 

{
  "containers": {
    "cna": {
      "affected": [
        {
          "defaultStatus": "unaffected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/protocol.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "lessThan": "625fc6060864889fe3d370cdeffbbab762af3cb4",
              "status": "affected",
              "version": "ee458a3f314e9c669ddd227bf5ab08354d9e75cc",
              "versionType": "git"
            },
            {
              "lessThan": "bd7aae448f6ee9d82599a4474664de1e6e91a535",
              "status": "affected",
              "version": "ee458a3f314e9c669ddd227bf5ab08354d9e75cc",
              "versionType": "git"
            }
          ]
        },
        {
          "defaultStatus": "affected",
          "product": "Linux",
          "programFiles": [
            "net/mptcp/protocol.c"
          ],
          "repo": "https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git",
          "vendor": "Linux",
          "versions": [
            {
              "status": "affected",
              "version": "6.19"
            },
            {
              "lessThan": "6.19",
              "status": "unaffected",
              "version": "0",
              "versionType": "semver"
            },
            {
              "lessThanOrEqual": "7.1.*",
              "status": "unaffected",
              "version": "7.1.6",
              "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": "7.1.6",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                },
                {
                  "criteria": "cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*",
                  "versionEndExcluding": "7.2",
                  "versionStartIncluding": "6.19",
                  "vulnerable": true
                }
              ],
              "negate": false,
              "operator": "OR"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "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."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "baseScore": 9.8,
            "baseSeverity": "CRITICAL",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H",
            "version": "3.1"
          },
          "scenarios": [
            {
              "lang": "en",
              "value": "AV:N - The bug is in MPTCP receive/teardown on the TCP/IP stack; remote peers drive subflow_data_ready() RX softirq processing and can concurrently trigger subflow close via FIN/RST or data floods during mptcp_close_ssk(), reaching the race without local access.\nAC:L - The attacker controls both sides of the race by timing inbound packets against subflow teardown on an MPTCP connection they own; syzkaller reliably reproduced the UAF, and no uncontrollable memory layout or rare victim state is required beyond an active MPTCP session.\nPR:N - Exploitation needs only the ability to be an MPTCP/TCP peer on the network after handshake; no local account, CAP_NET_ADMIN, or application credentials on the victim are required to send data and close subflows remotely.\nUI:N - No victim user interaction is required beyond the system normally accepting or maintaining MPTCP connections; the attacker can trigger the race entirely through automated network traffic and connection management.\nS:U - The vulnerability corrupts kernel heap memory within the network stack security boundary on the affected host; it does not by itself cross VM, hypervisor, or IOMMU isolation boundaries.\nC:H - A missed backlog cleanup leaves skb-\u003esk pointing at a freed subflow socket; later mptcp_backlog_purge() dereferences it in mptcp_borrow_fwdmem(), producing a slab use-after-free on struct sock that can disclose kernel memory.\nI:H - The UAF performs atomic_sub() writes to sk_rmem_alloc on a freed TCP socket object, corrupting attacker-influenced heap memory and providing a standard path to further arbitrary kernel write or control-flow hijack.\nA:H - Confirmed KASAN slab-use-after-free during mptcp_backlog_purge() causes inet_sock_destruct() warnings and kernel instability during socket teardown; UAF in softirq/close paths can panic or repeatedly crash the host."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-17T05:00:11.808Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4"
        },
        {
          "url": "https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535"
        }
      ],
      "title": "mptcp: fix stale skb-\u003esk reference on subflow close",
      "x_generator": {
        "engine": "bippy-1.2.0"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2026-68170",
    "datePublished": "2026-08-10T11:59:39.174Z",
    "dateReserved": "2026-07-30T09:28:09.372Z",
    "dateUpdated": "2026-08-17T05:00:11.808Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-68170",
      "date": "2026-09-12",
      "epss": "0.00516",
      "percentile": "0.4242"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-68170\",\"sourceIdentifier\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"published\":\"2026-08-10T13:20:03.637\",\"lastModified\":\"2026-08-17T05:18:17.593\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"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.\"}],\"affected\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"affectedData\":[{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"unaffected\",\"programFiles\":[\"net/mptcp/protocol.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"ee458a3f314e9c669ddd227bf5ab08354d9e75cc\",\"lessThan\":\"625fc6060864889fe3d370cdeffbbab762af3cb4\",\"versionType\":\"git\",\"status\":\"affected\"},{\"version\":\"ee458a3f314e9c669ddd227bf5ab08354d9e75cc\",\"lessThan\":\"bd7aae448f6ee9d82599a4474664de1e6e91a535\",\"versionType\":\"git\",\"status\":\"affected\"}]},{\"vendor\":\"Linux\",\"product\":\"Linux\",\"defaultStatus\":\"affected\",\"programFiles\":[\"net/mptcp/protocol.c\"],\"repo\":\"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git\",\"versions\":[{\"version\":\"6.19\",\"status\":\"affected\"},{\"version\":\"0\",\"lessThan\":\"6.19\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.1.6\",\"lessThanOrEqual\":\"7.1.*\",\"versionType\":\"semver\",\"status\":\"unaffected\"},{\"version\":\"7.2\",\"lessThanOrEqual\":\"*\",\"versionType\":\"original_commit_for_fix\",\"status\":\"unaffected\"}]}]}],\"metrics\":{\"cvssMetricV31\":[{\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.1\",\"vectorString\":\"CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H\",\"baseScore\":9.8,\"baseSeverity\":\"CRITICAL\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"LOW\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"NONE\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"HIGH\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"HIGH\"},\"exploitabilityScore\":3.9,\"impactScore\":5.9}]},\"references\":[{\"url\":\"https://git.kernel.org/stable/c/625fc6060864889fe3d370cdeffbbab762af3cb4\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"},{\"url\":\"https://git.kernel.org/stable/c/bd7aae448f6ee9d82599a4474664de1e6e91a535\",\"source\":\"416baaa9-dc9f-4396-8d5f-8c081fb06d67\"}]}}",
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-08-31T11:17:47+00:00",
      "cve": "CVE-2026-68170",
      "id": "CVE-2026-68170",
      "initial_release_date": "2026-08-10T00:00:00+00:00",
      "product_status:known_not_affected": "277",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: mptcp: fix stale skb-\u003esk reference on subflow close",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-68170.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "moderate",
      "current_release_date": "2026-08-13T16:23:46Z",
      "cve": "CVE-2026-68170",
      "id": "CVE-2026-68170",
      "initial_release_date": "2026-08-13T16:23:46Z",
      "product_status:known_affected": "29",
      "product_status:known_not_affected": "267",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-68170",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-68170.json",
      "version": "2"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.





Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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.