Linux: Out-of-bounds Read
CVE-2025-21993 is a high-severity out-of-bounds read vulnerability in Linux, with a CVSS 3.1 base score of 7.1 out of 10. It can be exploited with local access to the system by an attacker with a low-privileged account, without any action from a user. The record lists versions a858cd58dea06cf85b142673deea8c5d87f11e70, f763c82db8166e28f45b7cc4a5398a7859665940, b388e185bfad32bfed6a97a6817f74ca00a4318f as the first without the flaw, so updating Linux to one of those releases or later removes the exposure. There is no confirmed exploitation so far. EPSS estimates a 0.22% chance of exploitation within 30 days, which is low compared with other CVEs.
High severity with no evidence of exploitation so far.
What to do
- Update Linux to a858cd58dea06cf85b142673deea8c5d87f11e70 or f763c82db8166e28f45b7cc4a5398a7859665940 or b388e185bfad32bfed6a97a6817f74ca00a4318f or 9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c, whichever matches your release line, or a later version.
- Update Linux Kernel to 6.1.132 or 6.6.84 or 6.12.20 or 6.13.8, whichever matches your release line, or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, a858cd58dea06cf85b142673deea8c5d87f11e70; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, f763c82db8166e28f45b7cc4a5398a7859665940; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, b388e185bfad32bfed6a97a6817f74ca00a4318f; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, 9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, 2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, b253660fac5e0e9080d2c95e3a029e1898d49afb; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, c1c6e527470e5eab0b2d57bd073530fbace39eab; 138fe4e069798d9aa948a5402ff15e58f483ee4e up to, but not including, 07e0d99a2f701123ad3104c0f1a1e66bce74d6e5; and 1 more ranges | a858cd58dea06cf85b142673deea8c5d87f11e70, f763c82db8166e28f45b7cc4a5398a7859665940, b388e185bfad32bfed6a97a6817f74ca00a4318f, 9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c, 2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d, b253660fac5e0e9080d2c95e3a029e1898d49afb |
| Linux | Linux Kernel | before 6.1.132; 6.2 up to, but not including, 6.6.84; 6.7 up to, but not including, 6.12.20; 6.13 up to, but not including, 6.13.8; 6.14 | 6.1.132, 6.6.84, 6.12.20, 6.13.8 |
Version data comes from the organisation that assigned the CVE. Confirm against the vendor advisory before deciding you are unaffected.
How the severity score breaks down
- Attack vector
- LocalThe attacker needs local access or must trick a user into running something.
- Attack complexity
- LowNo special conditions are needed; the attack works reliably.
- Privileges required
- LowA basic user account is enough.
- User interaction
- NoneNo action by a victim is required.
- Scope
- UnchangedImpact stays within the vulnerable component.
- Confidentiality
- HighAll data handled by the component can be read.
- Integrity
- NoneNothing can be modified.
- Availability
- HighThe component can be taken down completely.
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:H. Scored by NVD.
| Scoring system | Score | Severity | Scored by |
|---|---|---|---|
| CVSS 3.1 | 7.1 | High | NVD |
| CVSS 3.1 | 7.1 | High | CISA (ADP) |
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.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Out-of-bounds Read
The product reads data past the end, or before the beginning, of the intended buffer.
How developers prevent this class of flaw
- Use a language that provides appropriate memory abstractions.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: partial).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
- git.kernel.org/stable/c/07e0d99a2f701123ad3104c0f1a1e66bce74d6e5
- git.kernel.org/stable/c/2d1eef248107bdf3d5a69d0fde04c30a79a7bf5d
- git.kernel.org/stable/c/9bfa80c8aa4e06dff55a953c3fffbfc68a3a3b1c
- git.kernel.org/stable/c/a858cd58dea06cf85b142673deea8c5d87f11e70
- git.kernel.org/stable/c/b253660fac5e0e9080d2c95e3a029e1898d49afb
- git.kernel.org/stable/c/b388e185bfad32bfed6a97a6817f74ca00a4318f
- git.kernel.org/stable/c/c1c6e527470e5eab0b2d57bd073530fbace39eab
- git.kernel.org/stable/c/f763c82db8166e28f45b7cc4a5398a7859665940
Other references
Recent Out-of-bounds Read vulnerabilities
- 7.1 High severity
- 7.1 High severity
- 7.1 High severity
- 7.1 High severity
- 7.8 High severity
- 7.8 High severity
Spotted an error? Tell us.