CVE-2026-64044 (GCVE-0-2026-64044)

Vulnerability from cvelistv5 – Published: 2026-07-19 15:39 – Updated: 2026-08-05 12:38
VLAI
Title
ovpn: respect peer refcount in CMD_NEW_PEER error path
Summary
In the Linux kernel, the following vulnerability has been resolved: ovpn: respect peer refcount in CMD_NEW_PEER error path ovpn_nl_peer_new_doit()'s error path calls ovpn_peer_release() directly rather than ovpn_peer_put(), bypassing the kref. The accompanying comment ("peer was not yet hashed, thus it is not used in any context") holds for UDP but not for TCP. For UDP, the ovpn_socket union uses the .ovpn arm and never points back at a peer; UDP encap_recv looks up peers via the not-yet-populated hashtables, so the new peer is unreachable until ovpn_peer_add() publishes it. For TCP, ovpn_socket_new() sets ovpn_sock->peer and ovpn_tcp_socket_attach() publishes ovpn_sock via rcu_assign_sk_user_data(). From that moment until ovpn_socket_release() detaches in the error path, the TCP fd is fully wired: userspace recvmsg / sendmsg / close / poll on the fd, as well as the strparser-driven ovpn_tcp_rcv() path, can reach the peer through sk_user_data -> ovpn_sock->peer and bump its refcount via ovpn_peer_hold(). ovpn_tcp_socket_wait_finish() (called inside ovpn_socket_release()) drains strparser and the tx work, but does not synchronize with userspace syscall callers that already hold a peer reference. If ovpn_nl_peer_modify() or ovpn_peer_add() returns an error while such a caller is in flight - notably an ovpn_tcp_recvmsg() blocked in __skb_recv_datagram() on peer->tcp.user_queue - the direct ovpn_peer_release() destroys the peer while the caller still holds the reference, and the eventual ovpn_peer_put() from that caller operates on freed memory. Replace the direct destructor call with ovpn_peer_put() so the kref correctly defers destruction until the last reference is dropped. In the common case where no concurrent user is present, behaviour is unchanged: the kref hits zero immediately and ovpn_peer_release_kref() runs the same destructor. With this conversion ovpn_peer_release() has no callers outside peer.c - ovpn_peer_release_kref() in the same translation unit is the only remaining user - so make it static and drop its declaration from peer.h.
Severity
7.8 (High)
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Assigner
References
Impacted products
Vendor Product Version CPE status
Linux Linux Affected: 11851cbd60ea1e5abbd97619d69845ead99303d6 , < 8298834912d76dbc82c12b6b4ab7590ed2bb8ae5 (git)
Affected: 11851cbd60ea1e5abbd97619d69845ead99303d6 , < 0c3ef71879c0264de6c42463031d9e057da87840 (git)
Affected: 11851cbd60ea1e5abbd97619d69845ead99303d6 , < 1fef6614673ff0846d30acdeeaf3cf98bb5f6116 (git)
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Linux Linux Affected: 6.16
Unaffected: 0 , < 6.16 (semver)
Unaffected: 6.18.34 , ≤ 6.18.* (semver)
Unaffected: 7.0.11 , ≤ 7.0.* (semver)
Unaffected: 7.1 , ≤ * (original_commit_for_fix)
guessed Create a notification for this product.
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              "value": "AV:L - The bug is triggered from the OVPN_CMD_PEER_NEW genetlink handler reached only via local netlink syscalls; remote TCP data can participate in the race but cannot alone reach the premature ovpn_peer_release() error path.\nAC:L - Exploitation requires a race between a failing CMD_NEW_PEER netlink message and a concurrent local holder of a peer reference, and the attacker controls both sides by blocking recvmsg on the TCP fd while issuing the failing netlink command.\nPR:L - All OVPN genetlink operations require GENL_ADMIN_PERM (CAP_NET_ADMIN), and creating the ovpn interface requires the same capability, which an unprivileged user can obtain inside a user namespace.\nUI:N - No victim interaction is required; the attacker configures the ovpn interface, TCP socket, and concurrent threads themselves to trigger the error-path UAF.\nS:U - The UAF corrupts kernel heap memory and enables standard kernel privilege escalation within the same security authority, not a cross-boundary escape such as guest-to-host or IOMMU bypass.\nC:H - Use-after-free of struct ovpn_peer allows an attacker to read freed slab memory and obtain arbitrary kernel memory disclosure primitives.\nI:H - Use-after-free of struct ovpn_peer enables heap grooming and control of freed object contents, providing a path to arbitrary kernel memory writes and code execution.\nA:H - The UAF causes ovpn_peer_put() to operate on freed memory, which can trigger kernel oops, panic, or crash during reference decrements on corrupted kref state."
            }
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    "datePublished": "2026-07-19T15:39:29.869Z",
    "dateReserved": "2026-07-19T07:54:57.029Z",
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        "descriptions": [
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            "lang": "en",
            "value": "In the Linux kernel, the following vulnerability has been resolved:\n\novpn: respect peer refcount in CMD_NEW_PEER error path\n\novpn_nl_peer_new_doit()\u0027s error path calls ovpn_peer_release() directly\nrather than ovpn_peer_put(), bypassing the kref. The accompanying\ncomment (\"peer was not yet hashed, thus it is not used in any context\")\nholds for UDP but not for TCP.\n\nFor UDP, the ovpn_socket union uses the .ovpn arm and never points back\nat a peer; UDP encap_recv looks up peers via the not-yet-populated\nhashtables, so the new peer is unreachable until ovpn_peer_add()\npublishes it.\n\nFor TCP, ovpn_socket_new() sets ovpn_sock-\u003epeer and\novpn_tcp_socket_attach() publishes ovpn_sock via rcu_assign_sk_user_data().\nFrom that moment until ovpn_socket_release() detaches in the error path,\nthe TCP fd is fully wired: userspace recvmsg / sendmsg / close / poll\non the fd, as well as the strparser-driven ovpn_tcp_rcv() path, can\nreach the peer through sk_user_data -\u003e ovpn_sock-\u003epeer and bump its\nrefcount via ovpn_peer_hold().\n\novpn_tcp_socket_wait_finish() (called inside ovpn_socket_release())\ndrains strparser and the tx work, but does not synchronize with\nuserspace syscall callers that already hold a peer reference. If\novpn_nl_peer_modify() or ovpn_peer_add() returns an error while such\na caller is in flight - notably an ovpn_tcp_recvmsg() blocked in\n__skb_recv_datagram() on peer-\u003etcp.user_queue - the direct\novpn_peer_release() destroys the peer while the caller still holds\nthe reference, and the eventual ovpn_peer_put() from that caller\noperates on freed memory.\n\nReplace the direct destructor call with ovpn_peer_put() so the kref\ncorrectly defers destruction until the last reference is dropped.\nIn the common case where no concurrent user is present, behaviour is\nunchanged: the kref hits zero immediately and ovpn_peer_release_kref()\nruns the same destructor.\n\nWith this conversion ovpn_peer_release() has no callers outside peer.c\n- ovpn_peer_release_kref() in the same translation unit is the only\nremaining user - so make it static and drop its declaration from\npeer.h."
          }
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        "id": "CVE-2026-64044",
        "lastModified": "2026-09-02T21:11:32.317",
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                "confidentialityImpact": "HIGH",
                "integrityImpact": "HIGH",
                "privilegesRequired": "LOW",
                "scope": "UNCHANGED",
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        "vulnStatus": "Analyzed",
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    "redhat_vex": {
      "aggregate_severity": "None",
      "current_release_date": "2026-07-21T08:03:13+00:00",
      "cve": "CVE-2026-64044",
      "id": "CVE-2026-64044",
      "initial_release_date": "2026-07-19T00:00:00+00:00",
      "product_status:known_not_affected": "275",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "kernel: ovpn: respect peer refcount in CMD_NEW_PEER error path",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-64044.json",
      "version": "3"
    },
    "suse_vex": {
      "aggregate_severity": "important",
      "current_release_date": "2026-08-05T00:34:14Z",
      "cve": "CVE-2026-64044",
      "id": "CVE-2026-64044",
      "initial_release_date": "2026-07-21T13:00:46Z",
      "product_status:known_not_affected": "298",
      "source": "SUSE CSAF VEX",
      "status": "interim",
      "title": "SUSE CVE CVE-2026-64044",
      "url": "https://ftp.suse.com/pub/projects/security/csaf-vex/cve-2026-64044.json",
      "version": "3"
    }
  }
}



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