CyberSecBulletin
CVE-2026-18821NVD status: Analyzed

PowerVM Hypervisor: Out-of-bounds Write

Published Updated By the CyberSecBulletin desk

CVE-2026-18821 is a high-severity out-of-bounds write vulnerability in PowerVM Hypervisor from IBM, with a CVSS 3.1 base score of 8.8 out of 10. It can be exploited from the same local network by an unauthenticated attacker, without any action from a user. Affected PowerVM Hypervisor versions: FW1120.00; FW1110.00 through FW1110.30; FW1060.00 through FW1060.80, and others listed below. The record does not name a fixed version, so check the vendor advisory. There is no confirmed exploitation so far. EPSS estimates a 0.29% chance of exploitation within 30 days, which is low compared with other CVEs.

Next patch cycle

High severity with no evidence of exploitation so far.

What to do

  1. Update Power System S1122 (9824-22a) Firmware to fw1110.31 or a later version.
  2. Update Power System S1124 (9824-42a) Firmware to fw1110.31 or a later version.
  3. Update Power System S1122s (9824-22b) Firmware to fw1110.31 or a later version.
  4. Read the advisory on ibm.com for workarounds and exact fixed builds.

Affected products and versions

VendorProductAffected versionsFixed in
IBMPowerVM HypervisorFW1120.00; FW1110.00 through FW1110.30; FW1060.00 through FW1060.80; FW950.00 through FW950.H2Not stated
IBMPower System S1122 (9824-22a) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System S1124 (9824-42a) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System S1122s (9824-22b) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System S1114 (9824-41b) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System L1122 (9856-22h) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System L1124 (9856-42h) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System E1150 (9043-mru) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System S1112 (9242-21b) Firmwarefw1120.00Not stated
IBMPower System S1112 (9242-21t) Firmwarefw1120.00Not stated
IBMPower System E1080 (9080-hex) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System S1022 (9105-22a) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System S1024 (9105-42a) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System S1022s (9105-22b) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System S1014 (9105-41b) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System L1022 (9786-22h) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System L1024 (9786-42h) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System E1050 (9043-mrx) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System S1012 (9028-21b) Firmwarefw1060.00 up to, but not including, fw1060.81fw1060.81
IBMPower System E1180 (9080-heu) Firmwarefw1110.00 up to, but not including, fw1110.31; fw1120.00fw1110.31
IBMPower System S922 (9009-22g) Firmwarefw950.00 up to, but not including, fw950.h3fw950.h3
IBMPower System H922 (9223-22s) Firmwarefw950.00 up to, but not including, fw950.h3fw950.h3
IBMPower System S914 (9009-41g) Firmwarefw950.00 up to, but not including, fw950.h3fw950.h3
IBMPower System S924 (9009-42g) Firmwarefw950.00 up to, but not including, fw950.h3fw950.h3
IBMPower System H924 (9223-42s) Firmwarefw950.00 up to, but not including, fw950.h3fw950.h3

Version data comes from the organisation that assigned the CVE; 2 further products are omitted here. Confirm against the vendor advisory before deciding you are unaffected.

How the severity score breaks down

Attack vector
AdjacentThe attacker must be on the same local network segment.
Attack complexity
LowNo special conditions are needed; the attack works reliably.
Privileges required
NoneNo account or login is needed.
User interaction
NoneNo action by a victim is required.
Scope
UnchangedImpact stays within the vulnerable component.
Confidentiality
HighAll data handled by the component can be read.
Integrity
HighData or code can be modified at will.
Availability
HighThe component can be taken down completely.

Vector: CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H. Scored by NVD.

Scoring systemScoreSeverityScored by
CVSS 3.17.5HighCNA (us.ibm.com)
CVSS 3.18.8HighNVD

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.

Source: the CVE record as published by its numbering authority, via NVD and CVE.org.

The underlying weakness: Out-of-bounds Write

The product writes data past the end, or before the beginning, of the intended buffer.

How developers prevent this class of flaw

  • Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. For example, many languages that perform their own memory management, such as Java and Perl, are not subject to buffer overflows. Other languages, such as Ada and C#, typically provide overflow protection, but the protection can be disabled by the programmer. Be wary that a language's interface to native code may still be subject to overflows, even if the language itself is theoretically safe.
  • Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid. Examples include the Safe C String Library (SafeStr) by Messier and Viega, and the Strsafe.h library from Microsoft. These libraries provide safer versions of overflow-prone string-handling functions.
  • Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index checking. D3-SFCV (Stack Frame Canary Validation) from D3FEND discusses canary-based detection in detail.

More Out-of-bounds Write vulnerabilities (CWE-787)

Timeline

  1. CVE record published.
  2. CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
  3. Record last changed materially (score, affected products, status or references).

References

Other vulnerabilities in PowerVM Hypervisor

All PowerVM Hypervisor vulnerabilities

Recent Out-of-bounds Write vulnerabilities

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