CVE-2025-21993

UBSAN warning via negative IPv6 prefix shift

Published Apr 2, 2025 · Updated May 11, 2026

Shift-out-of-bounds in Linux iscsi_ibft allows local users to trigger a UBSAN warning by reading an IPv6 iBFT subnet-mask entry. In ibft_attr_show_nic(), a 64-bit IPv6 prefix length is subtracted from 32 and used as a shift exponent while formatting the IPv4-style subnet-mask sysfs attribute. Reachability requires an ACPI iBFT table with an IPv6 prefix longer than 32 bits during iSCSI boot, a hardware or firmware condition that attackers cannot control; published material documents the warning rather than a controlled disclosure or service interruption.

CVSS severity7.1
High
EPSS probability0.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Shift-out-of-bounds in Linux iscsi_ibft allows local users to trigger a UBSAN warning by reading an IPv6 iBFT subnet-mask entry. In ibft_attr_show_nic(), a 64-bit IPv6 prefix length is subtracted from 32 and used as a shift exponent while formatting the IPv4-style subnet-mask sysfs attribute. Reachability requires an ACPI iBFT table with an IPv6 prefix longer than 32 bits during iSCSI boot, a hardware or firmware condition that attackers cannot control; published material documents the warning rather than a controlled disclosure or service interruption.

The record

CVE
CVE-2025-21993
Published
Apr 2, 2025
Updated
May 11, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
CWE-125
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Apr 2, 2025CVE publishedPublication date reported by the CVE source.
  2. May 11, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <07e0d99a2f701123ad3104c0f1a1e66bce74d6e5
  2. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d
  3. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c
  4. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <a858cd58dea06cf85b142673deea8c5d87f11e70
  5. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <b253660fac5e0e9080d2c95e3a029e1898d49afb
  6. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <b388e185bfad32bfed6a97a6817f74ca00a4318f
  7. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <c1c6e527470e5eab0b2d57bd073530fbace39eab
  8. Affected versionversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <f763c82db8166e28f45b7cc4a5398a7859665940
  9. Affected versionversion=2.6.26

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=138fe4e069798d9aa948a5402ff15e58f483ee4e <07e0d99a2f701123ad3104c0f1a1e66bce74d6e5; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <a858cd58dea06cf85b142673deea8c5d87f11e70; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <b253660fac5e0e9080d2c95e3a029e1898d49afb; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <b388e185bfad32bfed6a97a6817f74ca00a4318f; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <c1c6e527470e5eab0b2d57bd073530fbace39eab; version=138fe4e069798d9aa948a5402ff15e58f483ee4e <f763c82db8166e28f45b7cc4a5398a7859665940; version=2.6.26

Published CVSS scores

7.1NIST NVDCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-125Out-of-bounds Read

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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