CVE-2025-21993: linux kernel Out-of-bounds Read — Fix

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.

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CVSS v3.1 Score

7.1

HIGH

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

Weakness Type (CWE)

CWE-125 Out-of-bounds Read

Affected Products

Vendor	Product	Versions
linux	linux_kernel	< 6.1.132
linux	linux_kernel	6.2 — 6.6.84
linux	linux_kernel	6.7 — 6.12.20
linux	linux_kernel	6.13 — 6.13.8
linux	linux_kernel	All

References

Advisories & Patches

https://git.kernel.org/stable/c/07e0d99a2f701123ad3104c0f1a1e66bce74d6e5 https://git.kernel.org/stable/c/2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d https://git.kernel.org/stable/c/9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c https://git.kernel.org/stable/c/a858cd58dea06cf85b142673deea8c5d87f11e70 https://git.kernel.org/stable/c/b253660fac5e0e9080d2c95e3a029e1898d49afb https://git.kernel.org/stable/c/b388e185bfad32bfed6a97a6817f74ca00a4318f https://git.kernel.org/stable/c/c1c6e527470e5eab0b2d57bd073530fbace39eab https://git.kernel.org/stable/c/f763c82db8166e28f45b7cc4a5398a7859665940

Other References

https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html

Frequently Asked Questions

What is CVE-2025-21993? +

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. It has a CVSS v3.1 base score of 7.1 (HIGH).

How severe is CVE-2025-21993? +

CVE-2025-21993 has a CVSS v3.1 score of 7.1 out of 10, rated HIGH. This is a high-severity vulnerability that should be prioritized for patching.

What products are affected by CVE-2025-21993? +

CVE-2025-21993 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.

How do I check if I'm vulnerable to CVE-2025-21993? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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