CVE-2025-2884: TCG TPM2.0 Buffer Overflow Vulnerability

CVE-2025-2884 Overview

CVE-2025-2884 is an out-of-bounds read vulnerability affecting the TCG TPM2.0 Reference Implementation's CryptHmacSign helper function. The vulnerability stems from a lack of validation between the signature scheme and the signature key's algorithm, allowing attackers with local access to potentially read sensitive memory contents or cause a denial of service condition.

Critical Impact

Local attackers can exploit this flaw to access sensitive cryptographic data stored in TPM memory or crash affected systems through out-of-bounds memory access.

Affected Products

• TCG TPM2.0 Reference Implementation
• libtpms implementations using vulnerable code
• Systems implementing TPM 2.0 Library Specification prior to Errata Revision 1.83

Discovery Timeline

• June 10, 2025 - CVE-2025-2884 published to NVD
• June 13, 2025 - Last updated in NVD database

Technical Details for CVE-2025-2884

Vulnerability Analysis

This vulnerability exists in the CryptHmacSign helper function within the TPM2.0 reference implementation. The core issue is insufficient validation when processing HMAC signing operations—specifically, the code fails to verify that the signature scheme's hash algorithm is compatible with the signature key's algorithm before proceeding with cryptographic operations.

When an attacker supplies a mismatched or invalid hash algorithm identifier, the function proceeds to access memory locations calculated based on the invalid algorithm value. This results in out-of-bounds memory reads that can expose sensitive cryptographic material or cause the TPM to abort operations unexpectedly.

The vulnerability requires local access and user interaction, meaning an attacker would need either physical access to the system or the ability to execute code locally with sufficient privileges to interact with the TPM subsystem.

Root Cause

The root cause is a missing input validation check in the CryptHmacSign function. The function did not verify that the provided hashAlg parameter represents a valid, implemented hash algorithm before using it to calculate memory offsets and access cryptographic data structures. This is classified as CWE-125 (Out-of-Bounds Read).

The vulnerable code path accepts signature scheme parameters without confirming:

1. The scheme's hash algorithm is a valid TPM hash algorithm
2. The hash algorithm is compatible with the signing key type
3. The digest size matches the expected size for the hash algorithm

Attack Vector

The attack vector is local, requiring an attacker to have local access to the target system. Exploitation involves sending crafted TPM2_Sign commands with intentionally mismatched signature schemes and key algorithms. The attacker can craft requests where:

1. A signing key is created or loaded with a specific algorithm
2. A TPM2_Sign command is issued with an incompatible or invalid hash algorithm in the signature scheme
3. The TPM processes the request without adequate validation, leading to out-of-bounds memory access

// Security patch in src/tpm2/SigningCommands.c - tpm2: Fix potential out-of-bound access & abort due to HMAC signing issue
 //      TPM_RC_SCHEME           the scheme is not compatible with sign key type,
 //                              or input scheme is not compatible with default
 //                              scheme, or the chosen scheme is not a valid
-//                              sign scheme
+//                              sign scheme, or the scheme hashAlg is not a
+//                              valid hash algorithm
 //      TPM_RC_TICKET           'validation' is not a valid ticket
 //      TPM_RC_VALUE            the value to sign is larger than allowed for the
 //                              type of 'keyHandle'
+//      TPM_RC_ATTRIBUTES       the key has the x509sign attribute and can't be
+//                              used in TPM2_Sign()
+//      TPM_RC_SIZE             the provided 'digest' does not match the size
+//                              of the scheme hashAlg digest

 TPM_RC
 TPM2_Sign(Sign_In*  in,  // IN: input parameter list

Source: GitHub Commit Change

// Security patch in src/tpm2/crypto/CryptHash_fp.h - tpm2: Fix potential out-of-bound access & abort due to HMAC signing issue
 //  Return Type: BOOL
 //      TRUE(1)         hashAlg is a valid, implemented hash on this TPM
 //      FALSE(0)        hashAlg is not valid for this TPM
-BOOL CryptHashIsValidAlg(TPM_ALG_ID hashAlg,  // IN: the algorithm to check
-			 BOOL       flag  // IN: TRUE if TPM_ALG_NULL is to be treated
-			 //     as a valid hash
+BOOL CryptHashIsValidAlg(TPM_ALG_ID hashAlg,        // IN: the algorithm to check
+			 BOOL       isAlgNullValid  // IN: TRUE if TPM_ALG_NULL is to be treated
+					    //     as a valid hash
 			 );

 //*** CryptHashGetAlgByIndex()

Source: GitHub Commit Change

Detection Methods for CVE-2025-2884

Indicators of Compromise

• Unexpected TPM abort events or error codes (TPM_RC_SCHEME, TPM_RC_SIZE) in system logs
• Abnormal TPM2_Sign command patterns with mismatched algorithm parameters
• System crashes or instability related to TPM operations
• Memory access violations originating from TPM-related processes or drivers

Detection Strategies

• Monitor system logs for TPM error codes, particularly TPM_RC_SCHEME and TPM_RC_FAILURE responses
• Implement TPM command auditing to detect unusual signing requests with invalid hash algorithm combinations
• Deploy endpoint detection rules to identify processes making abnormal TPM API calls
• Review TPM event logs for repeated failed signing operations that may indicate exploitation attempts

Monitoring Recommendations

• Enable TPM command auditing on critical systems to log all TPM2_Sign operations
• Configure security monitoring solutions to alert on TPM-related process crashes or abnormal terminations
• Implement behavioral analysis to detect unusual patterns of TPM API usage by applications
• Review firmware and driver logs for TPM subsystem errors that could indicate exploitation

How to Mitigate CVE-2025-2884

Immediate Actions Required

• Update libtpms installations to versions containing commit 04b2d8e9afc0a9b6bffe562a23e58c0de11532d1
• Review and apply the TPM 2.0 Library Specification Errata Revision 1.83
• Consult vendor-specific advisories for firmware updates (see Intel Security Advisory SA-01209)
• Audit systems to identify TPM implementations that may be affected

Patch Information

The vulnerability has been addressed in the TCG TPM 2.0 Library Specification Errata Revision 1.83. The fix adds proper validation to ensure the signature scheme's hash algorithm is valid and compatible before processing signing operations. The patch introduces additional return codes (TPM_RC_ATTRIBUTES, TPM_RC_SIZE) and validates that the digest size matches the scheme's hash algorithm digest size.

For technical details on the fix, refer to the libtpms security patch and the Trusted Computing Group Security Advisory.

Additional resources:

• TPM 2.0 Library Specification Errata
• CERT Vulnerability Report #282450

Workarounds

• Restrict local access to TPM interfaces to authorized users and applications only
• Implement application-level input validation before passing parameters to TPM functions
• Use application allowlisting to control which processes can interact with TPM subsystems
• Monitor and audit TPM operations on critical systems until patches can be applied

# Configuration example
# Restrict TPM device access to specific groups (Linux example)
sudo chmod 660 /dev/tpm0
sudo chgrp tss /dev/tpm0

# Verify TPM access permissions
ls -la /dev/tpm*

# Check for libtpms package version (Debian/Ubuntu)
dpkg -l | grep libtpms

# Update libtpms to patched version
sudo apt-get update && sudo apt-get upgrade libtpms0