CVE-2026-64158: In the Linux kernel, the following vulnerability has been resolved: netfs: Fix write streaming disablement if fd open O_RDWR In netfs_perform_write(...

Description

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix write streaming disablement if fd open O_RDWR In netfs_perform_write(), "write streaming" (the caching of dirty data in dirty but !uptodate folios) is performed to avoid the need to read data that is just going to get immediately overwritten. However, this is/will be disabled in three circumstances: if the fd is open O_RDWR, if fscache is in use (as we need to round out the blocks for DIO) or if content encryption is enabled (again for rounding out purposes). The idea behind disabling it if the fd is open O_RDWR is that we'd need to flush the write-streaming page before we could read the data, particularly through mmap. But netfs now fills in the gaps if ->read_folio() is called on the page, so that is unnecessary. Further, this doesn't actually work if a separate fd is open for reading. Fix this by removing the check for O_RDWR, thereby allowing streaming writes even when we might read. This caused a number of problems with the generic/522 xfstest, but those are now fixed.

Metrics

CVSS 3.1

7.3/10

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

EPSS Probability

0.08%

0.4th 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	>= c38f4e96e605f17990e871214e6ea1496bc4e65f, < 9adf8e47d73d5e3c2fe77dea649dcde350ccd65c; >= c38f4e96e605f17990e871214e6ea1496bc4e65f, < 616578e40dcba3f94810d841c5a52b7e3bc8ede7; >= c38f4e96e605f17990e871214e6ea1496bc4e65f, < 7a9fa5b020a3a40f8291a71cd44c08d931da430d; >= c38f4e96e605f17990e871214e6ea1496bc4e65f, < 70a7b9193bbbfceaab5974de66834c64ccc875dd
Linux	Linux	6.8

References

Timeline

Published: Jul 19, 2026
Last Modified: Jul 30, 2026
Status: Awaiting Analysis

Frequently Asked Questions

What is CVE-2026-64158?

In the Linux kernel, the following vulnerability has been resolved: netfs: Fix write streaming disablement if fd open O_RDWR In netfs_perform_write(), "write streaming" (the caching of dirty data in dirty but !uptodate folios) is performed to avoid the need to read data that is just going to get immediately overwritten. However, this is/will be disabled in three circumstances: if the fd is open O_RDWR, if fscache is in use (as we need to round out the blocks for DIO) or if content encryption is enabled (again for rounding out purposes). The idea behind disabling it if the fd is open O_RDWR is that we'd need to flush the write-streaming page before we could read the data, particularly through mmap. But netfs now fills in the gaps if ->read_folio() is called on the page, so that is unnecessary. Further, this doesn't actually work if a separate fd is open for reading. Fix this by removing the check for O_RDWR, thereby allowing streaming writes even when we might read. This caused a number of problems with the generic/522 xfstest, but those are now fixed.

How severe is CVE-2026-64158?

CVE-2026-64158 has a CVSS score of 7.3/10 (HIGH severity). The EPSS model estimates a 0.08% probability of exploitation in the next 30 days.

How do I fix CVE-2026-64158?

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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