CVE-2026-98400 s390/ipl: Fix NULL deref in kdump without re-IPL parm block
A NULL pointer dereference in the Linux kernel s390 IPL code causes a crash during kdump when specific boot parameters are missing.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-98400?
CVE-2026-98400 is a vulnerability in Linux, published on 14 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
s390/ipl: Fix NULL deref in kdump without re-IPL parm block
Some IPL types, like HMC FTP boot or QEMU direct kernel boot, might not provide an IPL parameter block. In this case, reipl_type_init() selects IPL_TYPE_UNKNOWN, and reipl_block_actual remains NULL.
kdump passes the re-IPL parameter block to the dump kernel through os_info. Before commit 3b9678472bab ("s390/ipl: correct kdump reipl block checksum calculation"), the os_info entry was added only for IPL types which initialized reipl_block_actual. That commit moved the os_info update to machine_crash_shutdown(), making it unconditional. As a result, set_os_info_reipl_block() dereferences reipl_block_actual for IPL_TYPE_UNKNOWN. This may happen to work by chance when address zero contains readable lowcore data and the resulting empty os_info entry is ignored by the dump kernel.
Skip the os_info update when no re-IPL parameter block is available. Kdump then collect the dump and reboot without setting re-IPL parameter block.
Which versions are affected by CVE-2026-98400?
How do I fix CVE-2026-98400?
Apply the vendor's patch.
Is CVE-2026-98400 being exploited?
There is no known exploitation of CVE-2026-98400 in the wild and no public exploit code.
Sources
Also known as AZL-108167, BELL-CVE-2026-98400, DEBIAN-CVE-2026-98400, GHSA-v8v9-cp6p-qm5r, UBUNTU-CVE-2026-98400.