CVE-2026-98845 in Linux
Summary
by MITRE • 10/18/2026
In the Linux kernel, the following vulnerability has been resolved:
tpm: Disable TPM on null key name mismatch
The null key name check exists to protect against TPM reset attacks, so a mismatch should stop the device from serving further requests. Currently it does not disable the chip when it finds a mismatch.
The mismatch is logged:
tpm tpm0: null key integrity check failed
but the chip keeps serving commands:
/ # tpm2_getcap -c properties-fixed TPM_PT_FAMILY_INDICATOR: as UINT32: 0x08322e3000 as string: "2.0" ...
tpm2_load_null() where the null key name check is run sets the chip as disabled only if the rc is non zero. When the mismatch is seen, rc is zero at that point and it returns success. The other issue is that the caller expects the null key handle to be populated when the function returns 0 which it does here without writing the handle and proceeds assuming the null key handle is valid.
During the test, I noticed that tpm2_start_auth_session() uses the uninitialized stack value as the key handle since tpm2_load_null() returns 0 despite the integrity failure and proceeds with TPM2_CC_START_AUTH_SESS with this value as salt key handle.
Set rc to -ENODEV on the mismatch. The error path then disables the chip and returns the correct code to the caller.
Tested in QEMU with swtpm and CONFIG_TCG_TPM2_HMAC=y by making TPM2_CC_CONTEXT_LOAD fail with TPM2_RC_INTEGRITY and changing the name of the re-created null key. The chip is now disabled on the mismatch.
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Analysis
by VulDB Data Team • 10/18/2026
The Linux kernel contains a critical logic flaw within the Trusted Platform Module subsystem that allows for potential security bypasses related to integrity verification failures during null key operations. This vulnerability specifically affects the handling of TPM reset attacks, where an attacker might attempt to manipulate the state of the hardware security module by causing mismatches in expected cryptographic keys or contexts. The core issue lies in the function tpm2_load_null, which is responsible for loading and verifying a null key used for authentication sessions. When this function detects that the actual name of the loaded key does not match the expected null key name, it logs an integrity check failure but fails to take appropriate defensive action against the compromised device state.
The technical root cause stems from incorrect error code handling within tpm2_load_null. The function is designed to disable the TPM chip if a mismatch occurs, thereby preventing further commands that could exploit the unstable or manipulated state of the hardware. However, the implementation sets the return code only when it is non-zero, and in cases where the integrity check fails due to a name mismatch, the internal logic erroneously results in a zero return value indicating success. Consequently, the caller interprets this as a successful operation rather than an error condition requiring device shutdown. This misinterpretation leads to the chip continuing to serve subsequent commands despite having failed its critical integrity verification step.
This flaw has significant operational implications for system security and data integrity. Because the TPM remains active after detecting a null key name mismatch, attackers can potentially exploit this window of opportunity to perform unauthorized operations or manipulate authentication sessions. Specifically, functions such as tpm2_start_auth_session rely on the handle returned by tpm2_load_null. Since the function returns success without properly populating the valid null key handle due to the earlier error path bypass, subsequent calls may utilize uninitialized stack values as key handles. This can lead to undefined behavior, potential crashes, or more severe exploitation vectors where an attacker gains unauthorized access to protected resources or manipulates cryptographic operations that should have been halted by the integrity failure mechanism.
The vulnerability aligns with CWE-252, which describes unchecked return value errors, and CWE-787, involving out-of-bounds write vulnerabilities if uninitialized memory is accessed in critical security contexts. From an ATT&CK perspective, this flaw could facilitate techniques related to Defense Evasion or Privilege Escalation by allowing attackers to bypass integrity checks that are meant to protect against tampering with the TPM state. The failure to disable the device upon detecting a mismatch undermines the fundamental trust model of hardware-based security modules, which rely on strict adherence to protocol and integrity constraints to maintain their protective capabilities.
To mitigate this vulnerability, developers have implemented a fix that explicitly sets the return code to -ENODEV when a null key name mismatch is detected. This change ensures that the error path correctly identifies the failure condition, triggering the necessary logic to disable the TPM chip immediately upon detection of an integrity violation. By returning the appropriate negative error code, the caller can accurately recognize the security event and refrain from proceeding with operations that depend on valid cryptographic handles. This correction restores the intended behavior where any deviation in null key verification results in immediate device shutdown, thereby preventing further exploitation attempts through manipulated TPM states or unauthorized command execution.
System administrators and developers should ensure that their Linux kernels are updated to include this patch, particularly for systems relying heavily on TPMs for secure boot, disk encryption, or hardware-backed authentication mechanisms. The fix addresses the specific logic error in tpm2_load_null while maintaining compatibility with existing configurations such as CONFIG_TCG_TPM2_HMAC. Validation of this mitigation involves testing scenarios where TPM context loading fails due to integrity errors and confirming that the device is correctly disabled rather than continuing to operate under compromised conditions. This ensures that the protective mechanisms against reset attacks function as designed, preserving the integrity and security posture provided by the Trusted Platform Module infrastructure.