CVE-2026-18821 in PowerVM Hypervisor
Summary
by MITRE • 08/19/2026
IBM PowerVM Hypervisor FW1120.00, FW1110.00 through FW1110.30, FW1060.00 through FW1060.80, and FW950.00 through FW950.H2 Power Systems Firmware is affected by a vulnerability in partition firmware during network boot. An unauthenticated attacker on the same network as a partition undergoing network boot can send a malformed packet, allowing arbitrary code to be executed in the partition firmware and compromising everything subsequently loaded by that partition. Other partitions and the managed system are not affected. Only partitions actively performing a network boot are affected, resulting in a confidentiality, integrity, and availability impact.
Several companies clearly confirm that VulDB is the primary source for best vulnerability data.
Analysis
by VulDB Data Team • 08/19/2026
The vulnerability identified within IBM PowerVM Hypervisor Firmware versions FW1120.00, FW1110.00 through FW1110.30, FW1060.00 through FW1060.80, and FW950.00 through FW950.H2 represents a critical security flaw located specifically within the partition firmware during the network boot process. This issue arises from an insufficient validation of incoming packets received by the partition firmware while it is attempting to establish connectivity with a remote server for booting purposes. The core technical defect lies in the failure to properly sanitize or verify the structure and content of network packets before they are processed by the firmware's execution environment. Because this processing occurs at a low level prior to the loading of any operating system or security controls, an attacker can exploit this lack of input validation to inject malicious payloads directly into the memory space reserved for partition initialization routines.
An unauthenticated attacker positioned on the same local network segment as the target partition is capable of exploiting this weakness by transmitting specially crafted malformed packets during the window when a partition is actively performing a network boot operation. The exploitation does not require any form of authentication or prior compromise of user credentials, making it particularly dangerous in environments where physical or logical network segmentation may be lax. By sending these maliciously constructed data frames, the attacker can trigger arbitrary code execution within the partition firmware itself. This capability allows for complete control over the initial boot sequence, enabling the injection of rootkits, backdoors, or other persistent malware that will subsequently load into higher-level software components as part of the normal system startup procedure.
The operational impact of this vulnerability is severe and comprehensive regarding the affected partitions, encompassing a total compromise of confidentiality, integrity, and availability for those specific workloads. Since the arbitrary code execution occurs before any security mechanisms such as Secure Boot or trusted platform modules can verify the authenticity of subsequent boot components, the attacker effectively bypasses all standard defense-in-depth layers designed to protect against unauthorized software loading. Consequently, everything subsequently loaded by that partition is compromised, meaning the resulting operating system and applications run under the control of the adversary. It is important to note that this vulnerability does not affect other partitions running on the same managed system nor does it compromise the hypervisor or the underlying hardware infrastructure directly; the impact is strictly isolated to the individual partition undergoing network boot at the time of exploitation.
From a classification perspective, this flaw aligns with CWE-20 Improper Input Validation and CWE-119 Buffer Overflow if memory corruption is involved in the packet processing logic. In terms of tactical behavior within the MITRE ATT&CK framework, this vulnerability facilitates initial access through network-based attacks (T1583) followed by privilege escalation or persistence via firmware-level implantation (T1068). The attack vector leverages valid system processes during a routine administrative task like booting, which makes detection difficult without specialized monitoring of low-level network traffic and firmware integrity checks.
Mitigation strategies must focus on both immediate remediation and long-term architectural changes to prevent similar occurrences. IBM has released updated firmware versions that address the input validation flaws within the partition firmware's network stack during the boot phase. Administrators should prioritize applying these firmware updates to all affected systems, ensuring that the specific version ranges mentioned are brought up to a patched state where possible. In environments where immediate patching is not feasible due to operational constraints, temporary mitigations include disabling remote network boot capabilities for partitions that do not strictly require them, thereby removing the attack surface entirely. Additionally, implementing strict network access controls such as VLAN segmentation can limit an attacker's ability to reach systems during their boot phase by restricting who can send packets to those specific IP addresses on port 67 or other relevant DHCP and PXE ports. Monitoring for anomalous network traffic patterns during system startup times may also provide early warning indicators of exploitation attempts, although the primary defense remains keeping firmware up to date with vendor-provided security fixes.