CVE-2026-64527
Received
Received - Intake
Buffer Overflow in Linux Kernel Hyper-V Video Driver
Vulnerability report for CVE-2026-64527, including description, CVSS score, EPSS score, affected products, exploitability, helpful resources, and attack-flow context.
Publication date: 2026-07-25
Last updated on: 2026-07-25
Assigner: kernel.org
Description
Description
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().
CVSS Scores
EPSS Scores
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Meta Information
Affected Vendors & Products
Currently, no data is known.
Helpful Resources
Exploitability
CWE
KEV
| CWE ID | Description |
|---|---|
| CWE-UNKNOWN |
