Linux Kernel Vulnerability in iSCSI Boot with IPv6

CVE-2025-21993

What is CVE-2025-21993?

A vulnerability in the Linux kernel affects iSCSI boot processes when using IPv6. Specifically, the use of the subnet-mask entry during iSCSI boot leads to the generation of a UBSAN shift-out-of-bounds warning. This occurs because the concept of a subnet mask does not apply to IPv6, and when iscsistart attempts to read this entry, it causes the shift exponent to become negative. To mitigate this issue, the value is set to ~0, effectively suppressing the warning message. It is important for users to ensure their systems are updated to avoid potential issues related to this misconfiguration.

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References