CVE-2026-4937 Overview
CVE-2026-4937 is an insufficient entropy vulnerability in IBM PowerVM Hypervisor firmware. Affected releases include FW1110.00 through FW1110.20, FW1060.00 through FW1060.71, and FW950.00 through FW950.H2. Certain hypervisor calls request cryptographic randomness but receive less entropy than expected. A local attacker with administrative privileges can leverage this weakness to decrypt data protected by the affected routines. The issue is tracked under CWE-331: Insufficient Entropy.
Critical Impact
A privileged local attacker can decrypt encrypted data handled by PowerVM Hypervisor calls, exposing sensitive workloads running on affected IBM Power firmware.
Affected Products
- IBM PowerVM Hypervisor FW1110.00 through FW1110.20
- IBM PowerVM Hypervisor FW1060.00 through FW1060.71
- IBM PowerVM Hypervisor FW950.00 through FW950.H2
Discovery Timeline
- 2026-08-19 - CVE-2026-4937 published to NVD
- 2026-08-20 - Last updated in NVD database
Technical Details for CVE-2026-4937
Vulnerability Analysis
The flaw resides in specific hypervisor calls exposed by IBM PowerVM. These calls request random bytes for cryptographic use, but the underlying implementation returns fewer bits of entropy than the interface advertises. Cryptographic operations built on this randomness inherit a reduced keyspace. An attacker with administrative access on a logical partition can invoke the affected calls, observe outputs, and reconstruct keys or nonces used by the hypervisor. The result is decryption of data that callers assumed was cryptographically protected. The vulnerability is a local attack that changes scope, meaning impact extends beyond the attacker's initial security context into other partitions or hypervisor-managed resources.
Root Cause
The root cause is insufficient entropy in a randomness source used by hypervisor calls [CWE-331]. The implementation supplies random data with fewer effective bits than the requested length. Consumers of these calls generate weak keys, predictable initialization vectors, or guessable nonces. Weak cryptographic primitives derived from this source can be brute-forced or recovered through statistical analysis. IBM has not published low-level implementation details for the affected HCALL interfaces.
Attack Vector
Exploitation requires local access with administrative privileges on a partition managed by the vulnerable PowerVM Hypervisor. The attacker issues affected hypervisor calls to collect randomness output or ciphertext produced with weakened keys. Offline cryptanalysis then recovers plaintext without additional interaction. High attack complexity reflects the specialized knowledge and access needed. No user interaction is required. See the IBM Support Page for vendor guidance.
No public proof-of-concept code has been released for CVE-2026-4937. The vulnerability is described in prose only; refer to the IBM advisory for firmware-level technical detail.
Detection Methods for CVE-2026-4937
Indicators of Compromise
- Unexpected hypervisor call patterns from administrative partitions targeting entropy or cryptographic service HCALL interfaces.
- Anomalous volumes of key generation or cryptographic operations originating from a single LPAR.
- Presence of firmware versions in the FW1110, FW1060, or FW950 families that have not been patched.
Detection Strategies
- Inventory all Power Systems and record active firmware levels to identify hosts running vulnerable builds.
- Correlate HMC audit logs with partition administrative actions to flag unusual hypervisor call activity.
- Monitor for unauthorized privilege elevation on LPARs that could enable an attacker to reach the affected calls.
Monitoring Recommendations
- Forward Hardware Management Console (HMC) and PowerVM audit events into a centralized SIEM for retention and correlation.
- Alert on firmware version drift and on partitions that fall behind IBM-recommended service packs.
- Track administrative logins to partitions and require multi-party approval for privileged sessions.
How to Mitigate CVE-2026-4937
Immediate Actions Required
- Apply the firmware fixes referenced on the IBM Support Page for FW1110, FW1060, and FW950.
- Restrict administrative access to LPARs and the HMC to a minimum set of trusted operators.
- Rotate cryptographic keys and secrets that may have been generated on affected hypervisor firmware.
Patch Information
IBM has published fixed firmware levels for the FW1110, FW1060, and FW950 streams. Consult the IBM Support Page for the exact service pack identifiers and installation instructions applicable to each Power Systems model.
Workarounds
- Where immediate patching is not possible, enforce strict separation of administrative duties on affected Power Systems.
- Avoid relying on hypervisor-provided randomness for high-value cryptographic material until firmware is updated.
- Increase logging and review of privileged partition activity to shorten dwell time for a local attacker.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
