CVE-2023-22745: TPM2 Software Stack Buffer Overflow Flaw

CVE-2023-22745 Overview

CVE-2023-22745 is a buffer overrun vulnerability affecting tpm2-tss, the open source software implementation of the Trusted Computing Group (TCG) Trusted Platform Module (TPM) 2 Software Stack (TSS2). The vulnerability exists in the Tss2_RC_SetHandler and Tss2_RC_Decode functions, which improperly index into the layer_handler array using an 8-bit layer number without proper bounds checking. Since the array only has TPM2_ERROR_TSS2_RC_LAYER_COUNT entries, attempting to add a handler for higher-numbered layers or decode a response code with such a layer number results in reads/writes past the end of the buffer.

Critical Impact

This buffer overrun vulnerability could result in arbitrary code execution. An example attack scenario involves a Man-in-the-Middle (MiTM) bus attack that returns 0xFFFFFFFF for the response code, triggering the out-of-bounds access.

Affected Products

• tpm2_software_stack versions prior to 4.1.0-rc0
• tpm2_software_stack versions prior to 4.0.1
• tpm2_software_stack versions prior to 3.2.2-rc1

Discovery Timeline

• 2023-01-19 - CVE CVE-2023-22745 published to NVD
• 2025-11-21 - Last updated in NVD database

Technical Details for CVE-2023-22745

Vulnerability Analysis

The vulnerability stems from insufficient bounds checking when handling TPM response codes. The layer_handler array is designed to store handler functions for different TSS2 error layers, but the code assumes that the 8-bit layer number extracted from response codes will always be within valid bounds. When a malicious or malformed response code contains a layer number exceeding TPM2_ERROR_TSS2_RC_LAYER_COUNT, both Tss2_RC_SetHandler (when registering handlers) and Tss2_RC_Decode (when processing responses) will access memory outside the allocated array.

Given that TPM modules are typically used for security-critical operations including secure boot, disk encryption, and credential storage, exploitation requires an attacker to have local access to the target machine with local system privileges. TPM access usually requires administrative privilege, which limits the attack surface but does not eliminate the risk for systems where attackers have already achieved privilege escalation.

Root Cause

The root cause is a classic buffer overflow due to insufficient input validation (CWE-120: Buffer Copy without Checking Size of Input). The layer_handler array has a fixed number of entries defined by TPM2_ERROR_TSS2_RC_LAYER_COUNT, but the layer number extracted from response codes is an 8-bit value (0-255), creating a mismatch between the possible input range and the array bounds.

Attack Vector

The attack vector requires local access with elevated privileges. An attacker could exploit this vulnerability through a Man-in-the-Middle attack on the TPM communication bus. By intercepting and modifying TPM response codes to include layer numbers outside the valid range (e.g., returning 0xFFFFFFFF), an attacker can trigger out-of-bounds memory access. Depending on the memory layout and system configuration, this could lead to:

1. Information disclosure through out-of-bounds reads
2. Denial of service through memory corruption
3. Arbitrary code execution through controlled out-of-bounds writes

/* SPDX-License-Identifier: BSD-2-Clause */
#ifdef HAVE_CONFIG_H
#include "config.h"
#endif
#include <assert.h>
#include <stdarg.h>
#include <stdbool.h>
#include <stdio.h>

Source: GitHub Commit - The patch adds bounds checking by including assert.h and implementing proper validation of layer numbers before array access.

Detection Methods for CVE-2023-22745

Indicators of Compromise

• Unexpected crashes or segmentation faults in applications using tpm2-tss libraries
• Abnormal TPM response codes with high layer numbers (particularly 0xFFFFFFFF)
• Memory access violations in processes interacting with TPM modules
• Suspicious modifications to TPM bus communication

Detection Strategies

• Monitor system logs for TPM-related errors and crashes in tpm2-tss dependent applications
• Implement runtime memory protection tools to detect out-of-bounds access attempts
• Use intrusion detection systems to monitor for unusual TPM bus activity
• Deploy application whitelisting to detect unauthorized code execution following potential exploitation

Monitoring Recommendations

• Enable verbose logging for TPM-related services and applications
• Monitor for processes accessing TPM with unusual response code patterns
• Implement file integrity monitoring on tpm2-tss library files to detect tampering
• Review system audit logs for privilege escalation attempts preceding TPM access

How to Mitigate CVE-2023-22745

Immediate Actions Required

• Update tpm2-tss to version 4.1.0-rc0, 4.0.1, or 3.2.2-rc1 or later immediately
• Review systems using TPM for signs of compromise
• Restrict physical access to systems with TPM modules
• Ensure administrative access to TPM-enabled systems is properly controlled and audited

Patch Information

The tpm2-software project has released patches in versions 4.1.0-rc0, 4.0.1, and 3.2.2-rc1. The fix ensures that the layer number is validated against TPM2_ERROR_TSS2_RC_LAYER_COUNT before being used to index into the layer_handler array. For detailed patch information, refer to:

• GitHub Security Advisory GHSA-4j3v-fh23-vx67
• Commit 306490c8d848c367faa2d9df81f5e69dab46ffb5

Workarounds

• Limit local access to systems with TPM modules to trusted administrators only
• Implement physical security controls for TPM bus connections to prevent MiTM attacks
• Use hardware security modules with additional integrity verification for critical systems
• Consider disabling TPM functionality temporarily on highly sensitive systems until patching is complete

# Check installed tpm2-tss version
pkg-config --modversion tss2-sys

# Update tpm2-tss on Debian/Ubuntu systems
sudo apt update && sudo apt install libtss2-dev

# Verify the patched version is installed
pkg-config --modversion tss2-sys