CVE-2025-38566 (GCVE-0-2025-38566)
Vulnerability from cvelistv5
Published
2025-08-19 17:02
Modified
2026-08-05 12:02
Severity ?
9.8 (Critical) - CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Summary
In the Linux kernel, the following vulnerability has been resolved: sunrpc: fix handling of server side tls alerts Scott Mayhew discovered a security exploit in NFS over TLS in tls_alert_recv() due to its assumption it can read data from the msg iterator's kvec.. kTLS implementation splits TLS non-data record payload between the control message buffer (which includes the type such as TLS aler or TLS cipher change) and the rest of the payload (say TLS alert's level/description) which goes into the msg payload buffer. This patch proposes to rework how control messages are setup and used by sock_recvmsg(). If no control message structure is setup, kTLS layer will read and process TLS data record types. As soon as it encounters a TLS control message, it would return an error. At that point, NFS can setup a kvec backed msg buffer and read in the control message such as a TLS alert. Msg iterator can advance the kvec pointer as a part of the copy process thus we need to revert the iterator before calling into the tls_alert_recv.
References
Impacted products
Vendor Product Version
Linux Linux Version: 5e052dda121e2870dd87181783da4a95d7d2927b
Version: 5e052dda121e2870dd87181783da4a95d7d2927b
Version: 5e052dda121e2870dd87181783da4a95d7d2927b
Version: 5e052dda121e2870dd87181783da4a95d7d2927b
Version: 5e052dda121e2870dd87181783da4a95d7d2927b
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{
  "containers": {
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          "programFiles": [
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      "cpeApplicability": [
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      "descriptions": [
        {
          "lang": "en",
          "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nsunrpc: fix handling of server side tls alerts\n\nScott Mayhew discovered a security exploit in NFS over TLS in\ntls_alert_recv() due to its assumption it can read data from\nthe msg iterator\u0027s kvec..\n\nkTLS implementation splits TLS non-data record payload between\nthe control message buffer (which includes the type such as TLS\naler or TLS cipher change) and the rest of the payload (say TLS\nalert\u0027s level/description) which goes into the msg payload buffer.\n\nThis patch proposes to rework how control messages are setup and\nused by sock_recvmsg().\n\nIf no control message structure is setup, kTLS layer will read and\nprocess TLS data record types. As soon as it encounters a TLS control\nmessage, it would return an error. At that point, NFS can setup a\nkvec backed msg buffer and read in the control message such as a\nTLS alert. Msg iterator can advance the kvec pointer as a part of\nthe copy process thus we need to revert the iterator before calling\ninto the tls_alert_recv."
        }
      ],
      "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 vulnerable code is nfsd\u0027s server-side RPC-over-TLS receive path (net/sunrpc/svcsock.c), driven entirely by TLS records arriving on the TCP/2049 listener; a remote peer triggers it by sending a TLS alert record.\nAC:L - The attacker deterministically controls every precondition \u2014 complete the TLS handshake, send exactly 2 bytes of an RPC fragment marker to set sk_tcplen=2, then send any TLS alert, which exactly consumes the 2-byte kvec and forces the iterator past the end of the stack array; it can be repeated on unlimited connections.\nPR:N - svcauth_tls_accept() processes the AUTH_TLS STARTTLS probe on the NULL procedure with no credentials, and svc_tcp_handshake_done() enables kTLS even when the peer presents no certificate (TLS_NO_PEERID); export/mtls policy is only enforced far later, so the bug is reachable entirely pre-authentication.\nUI:N - The nfsd service threads process incoming TLS records autonomously; no local user or administrator action is needed once the server is listening.\nS:U - The out-of-bounds read and pointer dereference occur within the kernel\u0027s own memory and security authority; no VM, IOMMU, or sandbox boundary is crossed.\nC:H - tls_alert_recv() reads kernel memory through an out-of-bounds kvec element (stack contents reinterpreted as a pointer) and, in the bvec path, through a struct page * reinterpreted as a data buffer \u2014 an unbounded-address kernel read whose result is reflected back to the attacker as an observable connection-teardown oracle (-ENOTCONN vs -EAGAIN).\nI:H - This is a genuine type confusion (struct bio_vec / stale stack memory consumed as struct kvec) plus an out-of-bounds array access, and attacker-supplied alert bytes are written into kernel RPC state (svsk-\u003esk_marker, rq_pages) outside the protocol\u0027s intended flow, with the confused read steering kernel control flow.\nA:H - Dereferencing the pointer-sized value read past the end of the stack-allocated kvec (frequently NULL or a non-canonical/unmapped address) faults inside an nfsd service thread, producing a kernel oops and taking down the NFS server."
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-05T12:02:56.367Z",
        "orgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
        "shortName": "Linux"
      },
      "references": [
        {
          "url": "https://git.kernel.org/stable/c/b1df394621710b312f0393e3f240fdac0764f968"
        },
        {
          "url": "https://git.kernel.org/stable/c/25bb3647d30a20486b5fe7cff2b0e503c16c9692"
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        {
          "url": "https://git.kernel.org/stable/c/3b549da875414989f480b66835d514be80a0bd9c"
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        {
          "url": "https://git.kernel.org/stable/c/6b33c31cc788073bfbed9297e1f4486ed73d87da"
        },
        {
          "url": "https://git.kernel.org/stable/c/bee47cb026e762841f3faece47b51f985e215edb"
        }
      ],
      "title": "sunrpc: fix handling of server side tls alerts",
      "x_generator": {
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  "cveMetadata": {
    "assignerOrgId": "416baaa9-dc9f-4396-8d5f-8c081fb06d67",
    "assignerShortName": "Linux",
    "cveId": "CVE-2025-38566",
    "datePublished": "2025-08-19T17:02:42.506Z",
    "dateReserved": "2025-04-16T04:51:24.025Z",
    "dateUpdated": "2026-08-05T12:02:56.367Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}


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