Bug 2552209 (CVE-2026-98403)

Summary: CVE-2026-98403 kernel: s390/boot: Avoid IPL parameter append past command line
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
Status: NEW --- QA Contact:
Severity: medium Docs Contact:
Priority: medium    
Version: unspecifiedCC: akhatavk, aos-team-art-private, asdas, dpaolell, jdelft, jupierce, lgarciaa, mbiarnes, ppalepu, ppostler, prdhamdh, rhel-process-autobot, sghai, sidsharm, suppawar, vlaad, watson-tool-maintainers
Target Milestone: ---Keywords: Security
Target Release: ---   
Hardware: All   
OS: Linux   
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A flaw was found in the Linux kernel's s390 boot code. This flaw can lead to a Denial of Service (DoS) through memory corruption during system startup. When the early boot command-line buffer is nearly full, appending Initial Program Load (IPL) parameters triggers an integer underflow, causing an out-of-bounds write outside the designated buffer. A user capable of specifying custom boot parameters can exploit this vulnerability during system initialization to crash the system.
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Description OSIDB Bzimport 2026-10-14 13:45:00 UTC 
In the Linux kernel, the following vulnerability has been resolved:

s390/boot: Avoid IPL parameter append past command line

A command line may occupy all but the terminating byte of
COMMAND_LINE_SIZE. In that case append_ipl_block_parm() passes a zero size
to the IPL parameter conversion helpers and points the destination one
byte past early_command_line. The helpers subtract one from the unsigned
size and write the converted parameter outside the command line buffer.

Convert the IPL parameter in the command line parsing buffer first. A
parameter beginning with '=' can then replace the existing command line
regardless of its length, while other parameters are appended only when
space remains.
Comment 1 gkamathe 2026-10-16 07:02:24 UTC 
Upstream advisory:
https://git.kernel.org/pub/scm/linux/security/vulns.git/plain/cve/published/2026/CVE-2026-98403.mbox