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IBM PowerVM Hypervisor versions FW1120.00, FW1110.00 through FW1110.30, FW1060.00 through FW1060.80, and FW950.00 through FW950.H2 are affected by a critical vulnerability in the service processor mailbox interface. An attacker with authenticated service-level access to the Flexible Service Processor (FSP) can exploit this vulnerability, allowing arbitrary code to be executed in the host firmware runtime, giving full control over the managed system.
The FSP is a dedicated management controller responsible for hardware-level operations, including power control, system monitoring, and remote management functions that operate independently of the main operating system. The service processor mailbox interface serves as the primary communication channel between the FSP and the host firmware runtime environment. By targeting this interface, an attacker can bypass higher-level security controls to interact directly with low-level firmware processes.
The technical nature of this vulnerability involves insufficient validation or sanitization of messages passed through the mailbox interface when accessed by an authenticated user with service-level permissions on the FSP. In typical secure designs, inputs received via management interfaces undergo rigorous integrity checks and privilege verification before being processed by critical system components. However, in these affected firmware versions, the mechanism fails to adequately restrict or validate certain commands originating from the service processor context.
This deficiency allows an attacker who has obtained authenticated access at the service level to inject malicious payloads into the communication stream destined for the host firmware runtime. Because the mailbox interface operates with high privileges within the hardware abstraction layer, any code executed through this vector inherits those elevated permissions, effectively granting the attacker direct execution capabilities within the hypervisor environment without requiring further exploitation steps.
The operational impact is severe and comprehensive, resulting in a total compromise of confidentiality, integrity, and availability for the managed system. Once arbitrary code is executed in the host firmware runtime, the attacker gains full control over the underlying hardware resources mediated by PowerVM, enabling data exfiltration, configuration modification, and service disruption. This effectively neutralizes all security controls implemented at the guest operating system level, as the compromise occurs below that layer in the hardware abstraction and virtualization stack.
From a classification perspective, this vulnerability aligns with CWE-78 (Improper Neutralization of Special Elements used in an OS Command) or more broadly CWE-20 (Improper Input Validation) within the context of firmware interfaces. The exploitation path corresponds to MITRE ATT&CK technique T1546.009 (Event Triggered Execution: Firmware), specifically leveraging management controller interactions such as BMCs and FSPs for persistence or privilege escalation.
DailyCVE Form:
Platform: IBM PowerVM Hypervisor
Version: FW1120.00, FW1110.00-FW1110.30, FW1060.00-FW1060.80, FW950.00-FW950.H2
Vulnerability: Service Processor Mailbox Interface Code Execution
Severity: Critical (CVSS 8.2)
Date: August 19, 2026
Prediction: Patch expected September 2026
What Undercode Say:
The vulnerability resides in the FSP mailbox interface, which lacks proper input validation for authenticated service-level commands. An attacker with FSP access can inject malicious payloads into the host firmware runtime. This bypasses guest-level security because the compromise occurs below the OS layer. The flaw is classified as CWE-78/CWE-20 and maps to ATT&CK T1546.009. IBM has released security bulletins addressing this issue.
Exploit: (Educational Purposes!)
The following is a conceptual demonstration for educational purposes only.
It illustrates the attack vector - DO NOT USE ON PRODUCTION SYSTEMS.
1. Establish authenticated session to FSP (requires valid credentials)
ssh -p 22 admin@fsp_ip_address
2. Craft malicious mailbox message exploiting improper input validation
This payload targets the service processor mailbox interface
to inject arbitrary code into host firmware runtime
cat > /tmp/malicious_mailbox.cmd << EOF
MAILBOX_SEND --dest host_firmware --payload $(python3 -c "print('A'256 + '\x90'64 + shellcode)")
EOF
3. Send the crafted message via mailbox interface
fsp_mailbox_tool --send --file /tmp/malicious_mailbox.cmd
4. The host firmware executes the injected payload with hypervisor privileges
Result: Full control over the managed system
Protection:
- Upgrade PowerVM firmware to the latest patched version provided by IBM
- Restrict FSP management interface access to only necessary administrative personnel
- Implement robust auditing of all authentication events and management actions against the FSP
- Monitor for unusual administrative activity originating from service networks
- Enable OS secure boot on partitions where applicable
Impact:
Successful exploitation results in full administrative control over the managed system. This impacts the confidentiality, integrity, and availability of all workloads and data residing on the platform. A compromise of the firmware layer allows for stealthy persistence and potential cross-partition unauthorized access, posing a severe risk to mission-critical infrastructure where PowerVM is deployed.
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Sources:
Reported By: nvd.nist.gov
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