CVE-2025-21993 iscsi_ibft: Fix UBSAN shift-out-of-bounds warning in ibft_attr_show_nic()

What is CVE-2025-21993?

CVE-2025-21993 is a high-severity vulnerability in Linux kernel, published on 2 Apr 2025. 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:

iscsi_ibft: Fix UBSAN shift-out-of-bounds warning in ibft_attr_show_nic()

When performing an iSCSI boot using IPv6, iscsistart still reads the /sys/firmware/ibft/ethernetX/subnet-mask entry. Since the IPv6 prefix length is 64, this causes the shift exponent to become negative, triggering a UBSAN warning. As the concept of a subnet mask does not apply to IPv6, the value is set to ~0 to suppress the warning message.

Weakness: CWE-125

Which versions are affected by CVE-2025-21993?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2025-21993?

Apply the vendor's patch.

Is CVE-2025-21993 being exploited?

There is no known exploitation of CVE-2025-21993 in the wild and no public exploit code.

Other vulnerabilities in Linux kernel

• CVE-2026-53266 Linux Kernel Out-of-Bounds Write Exploited High 8.8
• CVE-2013-6282 Linux Kernel Improper Input Validation Exploited High 8.8
• CVE-2022-0185 Linux Kernel Heap-Based Buffer Overflow Exploited High 8.4
• CVE-2013-2094 Linux Kernel Privilege Escalation Exploited High 8.4
• CVE-2026-53362 Linux Kernel Unspecified Exploited High 7.8

All Linux kernel vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-59769, AZL-59892, BELL-CVE-2025-21993, DEBIAN-CVE-2025-21993, GHSA-ghxc-pm62-h5fx, UBUNTU-CVE-2025-21993.