GHSA-86PX-9VHR-GG2J

Vulnerability from github – Published: 2026-07-25 12:31 – Updated: 2026-07-25 12:31
VLAI
Details

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

drm/hyperv: validate VMBus packet size in receive callback

hyperv_receive_sub() reads msg->vid_hdr.type and dispatches into one of four message-type branches without knowing how many bytes the host wrote into hv->recv_buf. The completion path then runs memcpy(hv->init_buf, msg, VMBUS_MAX_PACKET_SIZE), so the consumer that wakes on wait_for_completion_timeout() can read up to 16 KiB of residue from a prior message as if it were the response payload.

Pass bytes_recvd into hyperv_receive_sub() and reject any packet that does not cover the pipe + synthvid header. A single switch on msg->vid_hdr.type then computes the type-specific payload size: the three completion-driving types (SYNTHVID_VERSION_RESPONSE, SYNTHVID_RESOLUTION_RESPONSE, SYNTHVID_VRAM_LOCATION_ACK) fall through to a shared exit that requires that size before memcpy/complete, while SYNTHVID_FEATURE_CHANGE validates its own payload and returns before reading is_dirt_needed. Unknown types are dropped.

SYNTHVID_RESOLUTION_RESPONSE is variable length: the host fills resolution_count entries, not the full SYNTHVID_MAX_RESOLUTION_COUNT array. Validate the fixed prefix first so resolution_count can be read, bound it against the array, then require only the count-sized array, so the shorter responses the host actually sends are accepted.

Only run the sub-handler when vmbus_recvpacket() returned success. The memcpy length is bytes_recvd, which is bounded by VMBUS_MAX_PACKET_SIZE only on a successful receive; on -ENOBUFS vmbus_recvpacket() instead reports the required length, which can exceed hv->recv_buf, so copying bytes_recvd would read and write past the 16 KiB buffers. Gating on the success return keeps the copy bounded. The nonzero-return path is itself a malformed-message case and is now logged rather than silently skipped; channel recovery is not attempted.

Rejected packets are reported via drm_err_ratelimited() rather than silently dropped, matching the CoCo-hardened pattern in hv_kvp_onchannelcallback().

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{
  "affected": [],
  "aliases": [
    "CVE-2026-64527"
  ],
  "database_specific": {
    "cwe_ids": [],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-07-25T10:17:39Z",
    "severity": null
  },
  "details": "In the Linux kernel, the following vulnerability has been resolved:\n\ndrm/hyperv: validate VMBus packet size in receive callback\n\nhyperv_receive_sub() reads msg-\u003evid_hdr.type and dispatches into one\nof four message-type branches without knowing how many bytes the host\nwrote into hv-\u003erecv_buf. The completion path then runs\nmemcpy(hv-\u003einit_buf, msg, VMBUS_MAX_PACKET_SIZE), so the consumer that\nwakes on wait_for_completion_timeout() can read up to 16 KiB of\nresidue from a prior message as if it were the response payload.\n\nPass bytes_recvd into hyperv_receive_sub() and reject any packet that\ndoes not cover the pipe + synthvid header. A single switch on\nmsg-\u003evid_hdr.type then computes the type-specific payload size: the\nthree completion-driving types (SYNTHVID_VERSION_RESPONSE,\nSYNTHVID_RESOLUTION_RESPONSE, SYNTHVID_VRAM_LOCATION_ACK) fall through\nto a shared exit that requires that size before memcpy/complete, while\nSYNTHVID_FEATURE_CHANGE validates its own payload and returns before\nreading is_dirt_needed. Unknown types are dropped.\n\nSYNTHVID_RESOLUTION_RESPONSE is variable length: the host fills\nresolution_count entries, not the full SYNTHVID_MAX_RESOLUTION_COUNT\narray. Validate the fixed prefix first so resolution_count can be\nread, bound it against the array, then require only the count-sized\narray, so the shorter responses the host actually sends are accepted.\n\nOnly run the sub-handler when vmbus_recvpacket() returned success. The\nmemcpy length is bytes_recvd, which is bounded by VMBUS_MAX_PACKET_SIZE\nonly on a successful receive; on -ENOBUFS vmbus_recvpacket() instead\nreports the required length, which can exceed hv-\u003erecv_buf, so copying\nbytes_recvd would read and write past the 16 KiB buffers. Gating on the\nsuccess return keeps the copy bounded. The nonzero-return path is itself\na malformed-message case and is now logged rather than silently skipped;\nchannel recovery is not attempted.\n\nRejected packets are reported via drm_err_ratelimited() rather than\nsilently dropped, matching the CoCo-hardened pattern in\nhv_kvp_onchannelcallback().",
  "id": "GHSA-86px-9vhr-gg2j",
  "modified": "2026-07-25T12:31:39Z",
  "published": "2026-07-25T12:31:39Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-64527"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/049a6b474823049fe60212f25f26e4b30f44ee8f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/164dc7bf17609340233c6bf4f66bb7c7008a0511"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/57d5d697642e05d5dd2d40660817765943dd709f"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/588c84b461393ff1998ac7b97b04f953f642e0df"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/7f87763f47a3c22fb50265a00619ef10f2394b18"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/c8974d96b6a5496f33dc69a3ce28a7bf5078def4"
    },
    {
      "type": "WEB",
      "url": "https://git.kernel.org/stable/c/f5251226551bfec98c4705641b6f94ff1f238d91"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}



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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.

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