CVE-2025-49133 in libtpms
Summary
by MITRE • 06/10/2025
Libtpms is a library that targets the integration of TPM functionality into hypervisors, primarily into Qemu. Libtpms, which is derived from the TPM 2.0 reference implementation code published by the Trusted Computing Group, is prone to a potential out of bounds (OOB) read vulnerability. The vulnerability occurs in the ‘CryptHmacSign’ function with an inconsistent pairing of the signKey and signScheme parameters, where the signKey is ALG_KEYEDHASH key and inScheme is an ECC or RSA scheme. The reported vulnerability is in the ‘CryptHmacSign’ function, which is defined in the "Part 4: Supporting Routines – Code" document, section "7.151 - /tpm/src/crypt/CryptUtil.c ". This vulnerability can be triggered from user-mode applications by sending malicious commands to a TPM 2.0/vTPM (swtpm) whose firmware is based on an affected TCG reference implementation. The effect on libtpms is that it will cause an abort due to the detection of the out-of-bounds access, thus for example making a vTPM (swtpm) unavailable to a VM. This vulnerability is fixed in 0.7.12, 0.8.10, 0.9.7, and 0.10.1.
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Analysis
by VulDB Data Team • 07/30/2025
The vulnerability identified as CVE-2025-49133 affects libtpms, a critical library that enables TPM functionality integration into virtualization environments, particularly Qemu hypervisors. This library serves as a bridge between virtualized environments and trusted platform module capabilities, making it a prime target for attackers seeking to compromise virtual machine security. The vulnerability stems from an inconsistent parameter handling within the CryptHmacSign function, which is part of the TPM 2.0 reference implementation codebase maintained by the Trusted Computing Group. This implementation flaw creates a dangerous condition where the library processes cryptographic operations with mismatched key and scheme parameters, leading to exploitable memory access patterns.
The technical flaw manifests specifically within the CryptHmacSign function located in the TPM source code at "Part 4: Supporting Routines – Code" document, section "7.151 - /tpm/src/crypt/CryptUtil.c". The vulnerability occurs when the signKey parameter is configured as an ALG_KEYEDHASH key type while the inScheme parameter is set to either ECC or RSA cryptographic schemes. This parameter mismatch creates an out-of-bounds read condition where the library attempts to access memory locations beyond the allocated buffer boundaries. The inconsistency between key types and scheme parameters causes the cryptographic library to incorrectly calculate memory offsets during HMAC signing operations, resulting in unauthorized memory access patterns that violate fundamental security assumptions.
From an operational perspective, this vulnerability poses significant risks to virtualized environments that rely on TPM functionality for security operations. Attackers can trigger this condition through user-mode applications by crafting malicious TPM 2.0 commands directed at vulnerable swtpm implementations. The exploitation results in immediate system aborts due to the detection of out-of-bounds memory access violations, effectively rendering the vTPM instance unavailable to guest virtual machines. This disruption can lead to complete service outages for VMs that depend on TPM-based authentication, encryption, or integrity verification mechanisms, particularly affecting cloud computing environments where multiple VMs share TPM resources. The vulnerability essentially creates a denial-of-service condition that can be exploited to disable critical security infrastructure within virtualized platforms.
The mitigation strategy involves upgrading to patched versions of libtpms, specifically versions 0.7.12, 0.8.10, 0.9.7, and 0.10.1, which contain the necessary code corrections to address the parameter validation issues. Organizations should prioritize patching their virtualization environments, particularly those running Qemu with libtpms integration, to prevent exploitation. Security monitoring should focus on detecting unusual TPM command sequences that might indicate attempts to trigger this vulnerability, and system administrators should implement proper access controls to limit exposure of TPM interfaces to untrusted applications. This vulnerability aligns with CWE-125 Out-of-bounds Read and ATT&CK technique T1486 Data Encrypted for Impact, as it can be leveraged to create denial-of-service conditions that compromise virtual machine security infrastructure. The fix addresses the root cause by implementing proper parameter validation and ensuring consistent handling of cryptographic key and scheme combinations within the HMAC signing routines.