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CVE-2026-4937 is a cryptographic weakness vulnerability identified in the IBM PowerVM Hypervisor firmware. The flaw resides in the entropy selection mechanism within the hypervisor’s cryptographic operations. When certain hypervisor calls are made to perform encryption on behalf of hosted logical partitions (LPARs) or administrative interfaces, the system requests cryptographic randomness but the implementation under-fills the entropy pool, utilizing less entropy than requested. This reduces the effective key space for encryption operations, making the resulting ciphertext statistically weaker than intended.
The vulnerability is classified under CWE-331 (Insufficient Entropy), where insufficient entropy used during encryption can lead to predictable output or reduced brute-force resistance. The attack surface is limited to the local environment: an attacker must already possess administrative privileges on a system interacting with the hypervisor, such as a privileged user on a logical partition or the Hypervisor Management Console (HMC). The attack complexity is rated High (AC:H), indicating that successful exploitation requires significant effort or specific conditions.
The reduced entropy would likely manifest in several ways: encryption keys partially determined or predictable; initialization vectors (IVs) reused or generated from a weak source; or padding and nonce values that fall into patterns across transactions. The vulnerability affects IBM PowerVM Hypervisor firmware across three release families: FW1110.00 through FW1110.20, FW1060.00 through FW1060.71, and FW950.00 through FW950.H2. Impacted systems include IBM Power Systems generations Power 9, Power 10, and Power 11, with specific models including Power System E1180, E1080, S1122, S1124, E1150, S1022, S1024, E1050, S922, H922, S914, S924, H924, E950, and E980.
Although the CVSS score of 5.3 denotes moderate severity, and the flaw requires local access with administrative privileges, the confidential impact is rated High (C:H) with a scope change to affected resources beyond the vulnerable component. This makes the vulnerability a significant concern for organizations relying on PowerVM logical partitioning for sensitive data isolation.
DailyCVE Form:
Platform: IBM PowerVM Hypervisor
Version: FW1110.00-FW1110.20, FW1060.00-FW1060.71, FW950.00-FW950.H2
Vulnerability: Insufficient Entropy (CWE-331)
Severity: MEDIUM (CVSS 5.3-6.0)
Date: 2026-08-19
Prediction: Patch available (FW1110.30/FW1120.00/FW1060.72/FW950.H3)
What Undercode Say:
Check affected firmware version:
Check current PowerVM firmware level lsmcode -c
Verify if system is vulnerable:
Check firmware version against vulnerable ranges Vulnerable: FW1110.00 through FW1110.20 Vulnerable: FW1060.00 through FW1060.71 Vulnerable: FW950.00 through FW950.H2
Monitor for suspicious hypervisor call patterns:
Monitor hypervisor entropy-related calls errpt -a | grep -i entropy
Check for cryptographic operations with weak entropy:
Review system logs for entropy warnings grep -i "entropy" /var/log/messages
Exploit: (Educational Purposes!)
The exploitation of CVE-2026-4937 requires local administrative access to a logical partition or HMC. An attacker with privileged access can invoke certain hypervisor calls designed to perform cryptographic operations. Due to the insufficient entropy implementation, these calls generate encryption keys derived from fewer bits of randomness than requested. This weakens the cryptographic output, enabling the attacker to decrypt encrypted data that should be protected by the hypervisor. The reduced entropy could allow an attacker to perform brute-force attacks against encrypted data with significantly less computational effort than would be required against properly generated keys.
Conceptually, identify hypervisor calls handling entropy (Requires administrative privileges on the system)
Theoretical entropy analysis (educational demonstration) Monitor entropy pool size cat /proc/sys/kernel/random/entropy_avail
Protection:
IBM has released firmware updates to remediate this vulnerability. Customers should install FW1110.30(1110_125), FW1120.00(1120_159), or newer for Power 11 systems. For Power 10 systems, install FW1060.72(1060_171) / FW1060.80(1060_180), or newer. For Power 9 systems, install FW950.H3(950_230) or newer. IBM strongly recommends addressing the vulnerability immediately. Additional mitigation measures include restricting access to the FSP network interface and limiting administrative access to trusted users only. Organizations should also review and rotate any cryptographic keys that may have been generated using the vulnerable hypervisor entropy implementation.
Impact:
A local attacker with administrative privileges can decrypt encrypted data protected by the hypervisor. The vulnerability weakens cryptographic output and falls under CWE-331, enabling confidential data exposure. Although the attack requires local access and administrative privileges, the confidential impact is rated High with a scope change, meaning the impact extends beyond the vulnerable component to affect other resources. Affected systems include IBM Power Systems of generations Power 9, Power 10, and Power 11 across numerous models. The vulnerability is not listed in CISA KEV, indicating a low-to-moderate exploitation probability in the wild. However, any privileged user with access to the affected hypervisor environment could potentially decrypt sensitive data, underscoring the need for timely remediation.
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Sources:
Reported By: nvd.nist.gov
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