CVE-2026-18821 Power System Out-of-bounds Write

High 7.5 Published 19 Aug 2026 Updated 22 Aug 2026

An unauthenticated attacker can execute arbitrary code in partition firmware during network boot via malformed packets, compromising the partition's integrity and availability.

Exploited in the wild: Not known
Login needed: Not needed
Attackable: Local or same network only
Victim action needed: Not needed
Fix: None listed

What is CVE-2026-18821?

CVE-2026-18821 is a high-severity memory corruption vulnerability in IBM PowerVM Hypervisor, published on 19 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

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.

Weakness: CWE-787

Which versions are affected by CVE-2026-18821?

It affects 26 products.

Products include Ibm Power System E1050 \(9043-Mrx\) Firmware, Ibm Power System E1080 \(9080-Hex\) Firmware, Ibm Power System E1150 \(9043-Mru\) Firmware, Ibm Power System E1180 \(9080-Heu\) Firmware, Ibm Power System E950 \(9040-Mr9\) Firmware, Ibm Power System E980 \(9080-M9s\) Firmware and 20 more.

How do I fix CVE-2026-18821?

No fix has been published for CVE-2026-18821 yet. Limit exposure of the affected software until one is available.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-18821 being exploited?

There is no known exploitation of CVE-2026-18821 in the wild and no public exploit code.

Sources

Also known as GHSA-3c3p-64wc-c8w7.