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CVE-2026-98403: s390/boot: Avoid IPL parameter append past command line

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-14 · updated 2026-10-19

Description

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.

Affected products

• Linux kernel: 5.16 — fixed in 7.3

How to fix

Upgrade to a fixed version: Linux kernel 7.3. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/73eec5a0d55916d7e1115f5d03a7ffc06d6215cf
• https://git.kernel.org/stable/c/8d11bfec8666f8409fac9072e9c25b691d3e30ac
• https://git.kernel.org/stable/c/af9866021a00ab9eeacf0c33ee73f3d134b4ed70
• https://git.kernel.org/stable/c/d76181dfabdaa720703167393704efacba343442

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