CVE-2022-29278 - How Faulty Pointer Checks in NvmExpressDxe Risk Both SMRAM and OS Memory

In this post, we’ll look closely at CVE-2022-29278, a significant firmware-level security hole discovered in the NvmExpressDxe driver. The flaw can potentially let attackers tamper with Secure Management RAM (SMRAM) and system memory on affected devices. We’ll break down what this means, how it’s possible, show some code examples, and—crucially—discuss how it can be fixed.

What Is CVE-2022-29278?

CVE-2022-29278 is a vulnerability caused by incorrect pointer checks in the NvmExpressDxe driver. This is a UEFI (Unified Extensible Firmware Interface) driver used by many systems to handle NVMe (Non-Volatile Memory express) storage devices during boot.

The crux of this issue is that NvmExpressDxe did not properly validate memory pointers. That means an attacker could craft malicious input and force the driver to use pointers that point outside allowed memory—like into SMRAM (where the System Management Mode code and secrets live), or into main OS memory. This opens the door for attacks like SMRAM tampering, privilege escalation, and much worse.

Who Discovered It and When?

The vulnerability was originally found by Insyde Software during an internal security review. Insyde provides UEFI firmware to many popular laptop, desktop, and server manufacturers. They announced the issue as part of their coordinated disclosure efforts.

Reference: Insyde Security Advisory SA-2022061

Who’s Affected?

Any system running vulnerable versions of the Insyde NvmExpressDxe driver. That includes desktops, laptops, and servers from companies using Insyde’s firmware. Since this is low-level code, it could potentially be triggered far before your operating system (Windows, Linux, etc.) even loads!

The driver accepts memory buffers from untrusted sources.

- It doesn’t check that those pointers actually belong to safe regions of memory (like within main DRAM).
- If a pointer points into sensitive areas (SMRAM or even certain parts of OS memory), and the driver uses it, critical data in those regions can be read/written improperly.

In effect, *trusted firmware code is tricked into messing with memory it shouldn't touch*.

Example of Incorrect Pointer Checks

Here’s a generic, simplified code example showing what a bad check might look like (in C-like pseudocode):

// BAD: No pointer validation
void NvmeRead(void* buffer, size_t length) {
    // ... code that trusts 'buffer' came from a valid place
    memcpy(buffer, NvmeStorage, length);
}

The code above just assumes ‘buffer’ is ok. If someone passes a pointer to SMRAM or protected OS memory, the contents there could get silently overwritten!

A better version would check the pointer against a whitelist of valid ranges

// GOOD: Pointer validation added!
bool is_in_valid_range(void* ptr, size_t length) {
    // Only allow pointers inside DRAM between SAFE_START and SAFE_END
    return ((uintptr_t)ptr >= SAFE_START) &&
           (((uintptr_t)ptr + length) <= SAFE_END);
}

void NvmeRead(void* buffer, size_t length) {
    if (!is_in_valid_range(buffer, length)) {
        printf("Pointer validation failed!\n");
        return;
    }
    memcpy(buffer, NvmeStorage, length);
}

Pass a crafted pointer that targets SMRAM.

2. Use the driver to read or write data into SMRAM, which is supposed to be *totally off-limits* for code running outside System Management Mode (SMM).
3. Change SMRAM content, potentially leading to SMM code execution with elevated privileges (“ring -2”), or to implant advanced firmware-level rootkits.

Alternatively, similar tricks could target OS memory, tampering with the kernel, bypassing OS/supervisor-level protections, or reading secrets from protected memory.

Example Exploit Concept (Pseudocode)

// Attacker sets up a pointer to SMRAM area
void* evilBuffer = (void*)SMRAM_BASE;
size_t length = x100;

// Attacker calls a vulnerable UEFI service
NvmeRead(evilBuffer, length);

// Now critical SMRAM content is overwritten if protections are not in place!

Real-world attacks would be more complex and might involve chaining several vulnerabilities. But this gives a flavor for what’s possible.

What Should You Do?

1. Check with your motherboard/laptop/PC vendor for UEFI/BIOS updates released summer/fall 2022 or later.

Apply any security updates they offer.

3. If you’re in charge of firmware development, audit any code that deals with DMA or memory buffer pointers. Never trust pointers from untrusted sources!

Conclusion

CVE-2022-29278 is a stark reminder that *firmware bugs* can have devastating effects—sometimes bigger than any OS or application bug. Insecure pointer handling at the firmware level can undo all the security built into your software stack. Make sure your firmware is up to date, and be wary of any system where updates aren’t offered!

If you want more technical details or help finding out if your device is vulnerable, feel free to reach out or check with your vendor. Stay safe!

Timeline

Published on: 11/15/2022 22:15:00 UTC
Last modified on: 11/29/2022 14:27:00 UTC