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Medium severity5.5NVD Advisory· Published May 19, 2024· Updated May 12, 2026

CVE-2024-35944

CVE-2024-35944

Description

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

VMCI: Fix memcpy() run-time warning in dg_dispatch_as_host()

Syzkaller hit 'WARNING in dg_dispatch_as_host' bug.

memcpy: detected field-spanning write (size 56) of single field "&dg_info->msg" at drivers/misc/vmw_vmci/vmci_datagram.c:237 (size 24)

WARNING: CPU: 0 PID: 1555 at drivers/misc/vmw_vmci/vmci_datagram.c:237 dg_dispatch_as_host+0x88e/0xa60 drivers/misc/vmw_vmci/vmci_datagram.c:237

Some code commentry, based on my understanding:

544 #define VMCI_DG_SIZE(_dg) (VMCI_DG_HEADERSIZE + (size_t)(_dg)->payload_size) /// This is 24 + payload_size

memcpy(&dg_info->msg, dg, dg_size); Destination = dg_info->msg ---> this is a 24 byte structure(struct vmci_datagram) Source = dg --> this is a 24 byte structure (struct vmci_datagram) Size = dg_size = 24 + payload_size

{payload_size = 56-24 =32} -- Syzkaller managed to set payload_size to 32.

35 struct delayed_datagram_info { 36 struct datagram_entry *entry; 37 struct work_struct work; 38 bool in_dg_host_queue; 39 /* msg and msg_payload must be together. */ 40 struct vmci_datagram msg; 41 u8 msg_payload[]; 42 };

So those extra bytes of payload are copied into msg_payload[], a run time warning is seen while fuzzing with Syzkaller.

One possible way to fix the warning is to split the memcpy() into two parts -- one -- direct assignment of msg and second taking care of payload.

Gustavo quoted: "Under FORTIFY_SOURCE we should not copy data across multiple members in a structure."

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

A field-spanning write in the Linux kernel's VMCI datagram handler can trigger a memcpy warning, potentially leading to information disclosure or system crash.

Vulnerability

Overview

In the Linux kernel, the dg_dispatch_as_host() function in vmci_datagram.c performs a memcpy() from a vmci_datagram structure to a delayed_datagram_info structure. The destination field msg is only 24 bytes, but the copy size dg_size includes the payload, which can be up to 32 bytes, causing a field-spanning write. This is detected by FORTIFY_SOURCE as a run-time warning, as memcpy should not copy data across multiple members of a structure [1].

Exploitation

Conditions

The vulnerability is reachable from user space via the VMCI socket interface. An attacker with local access can send a crafted datagram with a payload size set to 32 bytes (the example from Syzkaller). No authentication is required beyond the ability to interact with VMCI devices, which typically requires local user privileges.

Impact

If triggered, the warning indicates a buffer write beyond the intended field. While the warning itself is a denial-of-service (system crash or hang) in debug builds, in production builds the write may corrupt adjacent memory in the delayed_datagram_info structure, potentially leading to information disclosure or further system compromise.

Mitigation

The fix, applied in the Linux kernel, splits the memcpy() into a direct assignment for the fixed-size header and a separate copy for the payload. Users should update to a patched kernel version containing the commit. The vulnerability is also listed in Siemens advisory SSA-265688 for affected SIMATIC products [1].

References
  1. SSA-265688

AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

152

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

12

News mentions

0

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