CVE-2026-4936 in PowerVM Hypervisor
Summary
by MITRE • 08/20/2026
IBM PowerVM Hypervisor Platform KeyStore (PKS) and virtual TPM FW1110.00 through FW1110.20, FW1060.00 through FW1060.71, and FW950.00 through FW950.H2 use persistent storage key seeds that result in an AES key with reduced strength. An attacker with access to the service processor or HMC could exploit this weakness to derive the encryption key and access the data.
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Analysis
by VulDB Data Team • 08/20/2026
The vulnerability identified involves a critical cryptographic implementation flaw within the IBM PowerVM Hypervisor Platform, specifically affecting the KeyStore (PKS) component and virtual Trusted Platform Module versions FW1110.00 through FW1110.20, FW1060.00 through FW1060.71, and FW950.00 through FW950.H2. This issue stems from the use of persistent storage key seeds during the generation process for Advanced Encryption Standard keys. Instead of utilizing high-entropy random sources or robust derivation functions that ensure maximum entropy, the system relies on static or low-entropy seed values stored in non-volatile memory. This architectural decision results in AES encryption keys possessing significantly reduced strength compared to industry standards, thereby weakening the fundamental security guarantees provided by symmetric key cryptography.
From a technical perspective, this flaw aligns with CWE-327, which classifies the use of a broken or risky cryptographic algorithm as a weakness. The core issue is not necessarily that the AES algorithm itself is flawed, but rather how the keys are derived and managed. By using persistent storage seeds that may be predictable, static, or insufficiently randomized, the resulting key space becomes vulnerable to brute-force attacks or statistical analysis. An attacker who can access these seed values or infer them through side-channel observations can reconstruct the AES keys with far less computational effort than required for a properly implemented cryptographic system. This undermines the confidentiality and integrity protections that encryption is designed to provide within the virtualized environment.
The operational impact of this vulnerability is severe, particularly in multi-tenant cloud environments where data isolation between virtual machines relies heavily on strong encryption. An attacker who gains access to the Hardware Management Console or the service processor can exploit this weakness to derive the encryption keys used by the KeyStore and virtual TPM components. Once these keys are obtained, the attacker can decrypt sensitive data stored within the hypervisor's managed resources, including guest operating system images, configuration files, and potentially user credentials. This effectively bypasses the security boundaries established by the PowerVM platform, allowing unauthorized access to confidential information that was presumed to be protected at rest or in transit through these cryptographic mechanisms.
This exploitation scenario maps directly to several tactics within the MITRE ATT&CK framework. The initial access vector corresponds to T1078, Valid Accounts, as it requires legitimate but potentially compromised credentials for the service processor or HMC. The subsequent action of deriving encryption keys falls under T1539, Steal Web Session Cookie, if applied broadly to session data, or more accurately T1492, Stored Data on Cloud Infrastructure, in terms of targeting stored encrypted assets. Furthermore, the act of decrypting data using derived keys relates to T1028, Encrypted Channel, as it involves subverting encryption controls. The vulnerability essentially allows an insider threat or a compromised administrator account to escalate privileges and exfiltrate sensitive data without triggering typical intrusion detection alerts associated with brute-force attacks on strong cryptographic systems.
Mitigation strategies must focus on immediate remediation of the affected firmware versions and long-term architectural improvements. IBM has released updated firmware versions that address this issue by replacing the persistent storage key seeds with more robust, high-entropy random number generation methods for deriving AES keys. Administrators should immediately apply these patches to all systems running FW1110.21 or later, FW1060.72 or later, and FW950.H3 or later. In addition to patching, organizations should enforce strict access controls on the Hardware Management Console and service processor interfaces, ensuring that only authorized personnel have administrative privileges. Implementing multi-factor authentication for these management consoles can further reduce the risk of credential compromise leading to this exploitation path.
Long-term security posture improvements should include regular audits of cryptographic key generation processes across all virtualization platforms. Security teams must ensure that key derivation functions comply with NIST SP 800-132 guidelines for deriving keys from passwords or other secrets, emphasizing the use of salt and sufficient iteration counts to resist brute-force attacks. Additionally, monitoring tools should be configured to detect unusual access patterns to service processors and HMCs, as these are the primary vectors for exploiting this specific vulnerability. By combining timely patching with rigorous access control policies and continuous monitoring, organizations can effectively mitigate the risks associated with reduced cryptographic strength in their PowerVM environments.