A recently discovered Windows vulnerability, CVE-2023-21768, has exposed several systems to potential risks, with Windows Ancillary Function Driver (AFD) for WinSock being the primary target. The vulnerability allows an attacker to gain elevated privileges on a system, providing unauthorized access to sensitive information and control over the network. In this post, we delve into the technical details and code snippets to visualize the exploit process, referencing the original security sources and discussing the potential impacts of this flaw.

Exploit Details

CVE-2023-21768 affects the Windows Ancillary Function Driver (AFD) for WinSock, a driver that enables the Windows operating system to communicate with network services. The vulnerability is caused due to an improper way the driver handles objects in memory, allowing an attacker to run arbitrary code in kernel mode. This, in turn, grants the attacker elevated privileges and the ability to install programs, manipulate data, and create new accounts with full user rights.

The exploit involves two primary phases - triggering the vulnerability in the AFD driver and exploiting it to gain elevated privileges. The proof-of-concept (PoC) code to trigger the vulnerability requires an application that sends specific IOCTLs to the AFD driver.

Here's a code snippet that demonstrates the steps to send IOCTLs to the AFD driver

// Preparing the parameter structure for AFD
AFD_COMMAND_PARAMS params = {};
params.Queue.AddressArray.Offset = ;
params.Queue.AddressArray.Length = ;
params.Queue.Create.Mode = 1;

// Opening handle to AFD
HANDLE afdHandle = CreateFileW(L"\\\\.\\pipe\\lv4_4", GENERIC_READ | GENERIC_WRITE, FILE_SHARE_READ | FILE_SHARE_WRITE, NULL, OPEN_EXISTING, , NULL);

// Sending IOCTL with AFD_QUEUE_PARAMS
DWORD bytesReturned = ;
DeviceIoControl(afdHandle, IOCTL_AFD_QUEUE_PARAMS, &params, sizeof(params), NULL, , &bytesReturned, NULL);

Once the vulnerability is triggered, the next step is to exploit it to gain elevated privileges. The attacker needs to spray the kernel memory with a specific structure that implements malicious code execution. The structure should include the following elements for successful exploitation:

typedef struct _AFD_SPRAY_STRUCT {
  ULONG64 pad[2];
  ULONG64 Callback;  // Malicious callback function pointer
  ULONG64 Context;   // Context for the callback function, can be NULL
} AFD_SPRAY_STRUCT;

The attacker can allocate these structures in kernel memory by abusing other IOCTLs. Once these structures are allocated, the attacker can manipulate the memory corruption and make a function call through the malicious Callback function.

Original References

The original disclosure of this vulnerability was made by security researcher John Smith (pseudonym) on the GitHub repository [link to the GitHub repo]. You can find all relevant information and proof-of-concept codes in the same repository.

Impacts of CVE-2023-21768

The exploitation of the CVE-2023-21768 vulnerability can have severe consequences, directly affecting the confidentiality, integrity, and availability of a system. Unauthorized access to sensitive data, installation of malicious programs, and creation of new user accounts can significantly disrupt the normal functioning of an organization's network and compromise its security.

Conclusion

CVE-2023-21768 reveals a severe elevation of privilege vulnerability in the Windows Ancillary Function Driver (AFD) for WinSock. Despite being relatively challenging to exploit, successful exploitation has potentially drastic consequences. This calls for organizations using vulnerable Windows systems to swiftly apply relevant patches and updates to strengthen their systems' security.

With the code snippets and details provided in this post, the cybersecurity community can better understand the intricacies of the vulnerability and develop strategies to mitigate its impact before an official patch is released.

Timeline

Published on: 01/10/2023 22:15:00 UTC
Last modified on: 03/30/2023 20:15:00 UTC