Linux: Incorrect Calculation
CVE-2026-64388 is a high-severity incorrect calculation vulnerability in Linux, with a CVSS 3.1 base score of 7.8 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 c0fe1118a1471d459f76c3e70ff2abbf784ce6bf, 6825a45f6b8ef76b0ee32649ec3d6e39ca143a18, 27ead8c5418af6bfab711079fecb9414d78d4cae 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 0.13% 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 c0fe1118a1471d459f76c3e70ff2abbf784ce6bf or 6825a45f6b8ef76b0ee32649ec3d6e39ca143a18 or 27ead8c5418af6bfab711079fecb9414d78d4cae or 3eaec47518e126e6dcd1a48521d740278073f0ec, whichever matches your release line, or a later version.
- Update Linux Kernel to 7.1.4 or a later version.
Affected products and versions
| Vendor | Product | Affected versions | Fixed in |
|---|---|---|---|
| Linux | Linux | b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, c0fe1118a1471d459f76c3e70ff2abbf784ce6bf; b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, 6825a45f6b8ef76b0ee32649ec3d6e39ca143a18; b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, 27ead8c5418af6bfab711079fecb9414d78d4cae; b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, 3eaec47518e126e6dcd1a48521d740278073f0ec; b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, 550cfb8a81181331d4d0f76ab75ee58a0bf41e3e; b326614ea2159ea5c835d320f261d05d080cd201 up to, but not including, 760ef2c579c2609cf17fb1cd5392f64d42d43d33; 4.18 | c0fe1118a1471d459f76c3e70ff2abbf784ce6bf, 6825a45f6b8ef76b0ee32649ec3d6e39ca143a18, 27ead8c5418af6bfab711079fecb9414d78d4cae, 3eaec47518e126e6dcd1a48521d740278073f0ec, 550cfb8a81181331d4d0f76ab75ee58a0bf41e3e, 760ef2c579c2609cf17fb1cd5392f64d42d43d33 |
| Linux | Linux Kernel | 4.18 up to, but not including, 7.1.4 | 7.1.4 |
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
- HighData or code can be modified at will.
- 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:H/A:H. Scored by CNA.
Official description
In the Linux kernel, the following vulnerability has been resolved: smb/client: fix chown/chgrp with SMB3 POSIX Extensions Ownership (chown) and group (chgrp) modifications were being ignored when mounting with SMB3 POSIX Extensions unless CIFS_MOUNT_CIFS_ACL or CIFS_MOUNT_MODE_FROM_SID were also explicitly set. Fix this by checking for posix_extensions in cifs_setattr_nounix() when updating UID and GID, ensuring that id_mode_to_cifs_acl() is called to map and set the ownership/group information on the server.
Source: the CVE record as published by its numbering authority, via NVD and CVE.org.
The underlying weakness: Incorrect Calculation
The product performs a calculation that generates incorrect or unintended results that are later used in security-critical decisions or resource management.
How developers prevent this class of flaw
- Understand your programming language's underlying representation and how it interacts with numeric calculation. Pay close attention to byte size discrepancies, precision, signed/unsigned distinctions, truncation, conversion and casting between types, not-a-number calculations, and how your language handles numbers that are too large or too small for its underlying representation.
- Perform input validation on any numeric input by ensuring that it is within the expected range. Enforce that the input meets both the minimum and maximum requirements for the expected range.
- Use the appropriate type for the desired action. For example, in C/C++, only use unsigned types for values that could never be negative, such as height, width, or other numbers related to quantity.
Timeline
- CVE record published.
- CISA published its SSVC assessment (exploitation: none, automatable: no, technical impact: total).
- Record last changed materially (score, affected products, status or references).
References
Patches and release notes
Other references
Recent Incorrect Calculation vulnerabilities
- 9.8 Critical severity
- 8.1 High severity
- 7.5 High severity
- 8.6 High severity
- 7.8 High severity
- 8.3 High severity
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