Security Bulletin
Summary
The Linux kernel is used by the Virtualization Management Interface in PowerVM to support network communication with the Hardware Management Console. This bulletin provides a remediation for the impacted vulnerability, CVE-2026-31669, by upgrading PowerVM and thus addressing the exposure to the kernel vulnerability.
Vulnerability Details
CVEID: CVE-2026-31669
DESCRIPTION: In the Linux kernel, the following vulnerability has been resolved:
mptcp: fix slab-use-after-free in __inet_lookup_established
The ehash table lookups are lockless and rely on
SLAB_TYPESAFE_BY_RCU to guarantee socket memory stability
during RCU read-side critical sections. Both tcp_prot and
tcpv6_prot have their slab caches created with this flag
via proto_register().
However, MPTCP's mptcp_subflow_init() copies tcpv6_prot into
tcpv6_prot_override during inet_init() (fs_initcall, level 5),
before inet6_init() (module_init/device_initcall, level 6) has
called proto_register(&tcpv6_prot). At that point,
tcpv6_prot.slab is still NULL, so tcpv6_prot_override.slab
remains NULL permanently.
This causes MPTCP v6 subflow child sockets to be allocated via
kmalloc (falling into kmalloc-4k) instead of the TCPv6 slab
cache. The kmalloc-4k cache lacks SLAB_TYPESAFE_BY_RCU, so
when these sockets are freed without SOCK_RCU_FREE (which is
cleared for child sockets by design), the memory can be
immediately reused. Concurrent ehash lookups under
rcu_read_lock can then access freed memory, triggering a
slab-use-after-free in __inet_lookup_established.
Fix this by splitting the IPv6-specific initialization out of
mptcp_subflow_init() into a new mptcp_subflow_v6_init(), called
from mptcp_proto_v6_init() before protocol registration. This
ensures tcpv6_prot_override.slab correctly inherits the
SLAB_TYPESAFE_BY_RCU slab cache.
CWE: CWE-416: Use After Free
CVSS Source: Linux
CVSS Base score: 9.8
CVSS Vector: (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
Affected Products and Versions
| Affected Product(s) | Version(s) |
| Virtualization Management Interface | FW1110.00 - FW1110.31 |
| Virtualization Management Interface | FW1120.00 - FW1120.01 |
| Virtualization Management Interface | FW1060.00 - FW1060.81 |
For Power10 servers, a mitigation is being released only for FW1060 but all prior firmware releases on the listed products are vulnerable.
Remediation/Fixes
Power 11
1) IBM Power System S1122 (9824-22A)
2) IBM Power System S1124 (9824-42A)
3) IBM Power System S1122s (9824-22B)
4) IBM Power System S1114 (9824-41B)
5) IBM Power System L1122 (9856-22H)
6) IBM Power System L1124 (9856-42H)
7) IBM Power System E1150 (9043-MRU)
8) IBM Power System S1112 (9242-21B, 9242-21T)
The images mentioned above can be located at IBM Fix Central : https://www.ibm.com/support/fixcentral/
Power 10
1) IBM Power System S1022 (9105-22A)
2) IBM Power System S1024 (9105-42A)
3) IBM Power System S1022s (9105-22B)
4) IBM Power System S1014 (9105-41B)
5) IBM Power System L1022 (9786-22H)
6) IBM Power System L1024 (9786-42H)
7) IBM Power System E1050 (9043-MRX)
8) IBM Power System S1012 (9028-21B)
The images mentioned above can be located at IBM Fix Central : https://www.ibm.com/support/fixcentral/
Workarounds and Mitigations
None
Get Notified about Future Security Bulletins
References
Acknowledgement
Change History
23 Sep 2026: Initial Publication
*The CVSS Environment Score is customer environment specific and will ultimately impact the Overall CVSS Score. Customers can evaluate the impact of this vulnerability in their environments by accessing the links in the Reference section of this Security Bulletin.
Disclaimer
According to the Forum of Incident Response and Security Teams (FIRST), the Common Vulnerability Scoring System (CVSS) is an "industry open standard designed to convey vulnerability severity and help to determine urgency and priority of response." IBM PROVIDES THE CVSS SCORES ""AS IS"" WITHOUT WARRANTY OF ANY KIND, INCLUDING THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. CUSTOMERS ARE RESPONSIBLE FOR ASSESSING THE IMPACT OF ANY ACTUAL OR POTENTIAL SECURITY VULNERABILITY. In addition to other efforts to address potential vulnerabilities, IBM periodically updates the record of components contained in our product offerings. As part of that effort, if IBM identifies previously unidentified packages in a product/service inventory, we address relevant vulnerabilities regardless of CVE date. Inclusion of an older CVEID does not demonstrate that the referenced product has been used by IBM since that date, nor that IBM was aware of a vulnerability as of that date. We are making clients aware of relevant vulnerabilities as we become aware of them. "Affected Products and Versions" referenced in IBM Security Bulletins are intended to be only products and versions that are supported by IBM and have not passed their end-of-support or warranty date. Thus, failure to reference unsupported or extended-support products and versions in this Security Bulletin does not constitute a determination by IBM that they are unaffected by the vulnerability. Reference to one or more unsupported versions in this Security Bulletin shall not create an obligation for IBM to provide fixes for any unsupported or extended-support products or versions.
Document Location
Worldwide
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Document Information
Modified date:
23 September 2026
Initial Publish date:
23 September 2026
UID
ibm17288529