CVE-2025-40124: Linux Vulnerability (CVSS 7.8)

Description

In the Linux kernel, the following vulnerability has been resolved: sparc: fix accurate exception reporting in copy_{from_to}_user for UltraSPARC III Anthony Yznaga tracked down that a BUG_ON in ext4 code with large folios enabled resulted from copy_from_user() returning impossibly large values greater than the size to be copied. This lead to __copy_from_iter() returning impossible values instead of the actual number of bytes it was able to copy. The BUG_ON has been reported in https://lore.kernel.org/r/b14f55642207e63e907965e209f6323a0df6dcee.camel@physik.fu-berlin.de The referenced commit introduced exception handlers on user-space memory references in copy_from_user and copy_to_user. These handlers return from the respective function and calculate the remaining bytes left to copy using the current register contents. The exception handlers expect that %o2 has already been masked during the bulk copy loop, but the masking was performed after that loop. This will fix the return value of copy_from_user and copy_to_user in the faulting case. The behaviour of memcpy stays unchanged.

Metrics

CVSS 3.1

7.8/10

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

EPSS Probability

0.21%

11.0th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= ee841d0aff649164080e445e84885015958d8ff4, < fdd43fe6d286f27b826572457a89c926f97e2d3a; >= ee841d0aff649164080e445e84885015958d8ff4, < 1198077606aeffb102587c6ea079ce99641c99d4; >= ee841d0aff649164080e445e84885015958d8ff4, < 1857cdca12c4aff58bf26a7005a4d02850c29927; >= ee841d0aff649164080e445e84885015958d8ff4, < 91eda032eb16e5d2be27c95584665bc555bb5a90; >= ee841d0aff649164080e445e84885015958d8ff4, < dc766c4830a7e1e1ee9d7f77d4ab344f2eb23c8e; >= ee841d0aff649164080e445e84885015958d8ff4, < 5ef9c94d7110e90260c06868cf1dcf899b9f25ee; >= ee841d0aff649164080e445e84885015958d8ff4, < e50377c6b3f278c9f3ef017ffce17f5fcc9dace4; >= ee841d0aff649164080e445e84885015958d8ff4, < 47b49c06eb62504075f0f2e2227aee2e2c2a58b3; 1c7e17b1c4d60cc5aa575460f7efb73686dd3b39; ac663c54f40b2830b1ca32d1ae9d683fe248b14c; >= 4.4.34, < 4.5; >= 4.8.10, < 4.9
Linux	Linux	4.9

References

Timeline

Published: Nov 12, 2025
Last Modified: Jul 30, 2026
Status: Deferred

Frequently Asked Questions

What is CVE-2025-40124?

In the Linux kernel, the following vulnerability has been resolved: sparc: fix accurate exception reporting in copy_{from_to}_user for UltraSPARC III Anthony Yznaga tracked down that a BUG_ON in ext4 code with large folios enabled resulted from copy_from_user() returning impossibly large values greater than the size to be copied. This lead to __copy_from_iter() returning impossible values instead of the actual number of bytes it was able to copy. The BUG_ON has been reported in https://lore.kernel.org/r/b14f55642207e63e907965e209f6323a0df6dcee.camel@physik.fu-berlin.de The referenced commit introduced exception handlers on user-space memory references in copy_from_user and copy_to_user. These handlers return from the respective function and calculate the remaining bytes left to copy using the current register contents. The exception handlers expect that %o2 has already been masked during the bulk copy loop, but the masking was performed after that loop. This will fix the return value of copy_from_user and copy_to_user in the faulting case. The behaviour of memcpy stays unchanged.

How severe is CVE-2025-40124?

CVE-2025-40124 has a CVSS score of 7.8/10 (HIGH severity). The EPSS model estimates a 0.21% probability of exploitation in the next 30 days.

How do I fix CVE-2025-40124?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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