Bug 2397565 (CVE-2025-39888)

Summary: CVE-2025-39888 kernel: fuse: Block access to folio overlimit
Product: [Other] Security Response Reporter: OSIDB Bzimport <bzimport>
Component: vulnerabilityAssignee: Product Security DevOps Team <prodsec-dev>
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Version: unspecifiedKeywords: Security
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OS: Linux   
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An out-of-bounds write vulnerability exists in the linux kernel, such that in fuse_dev_do_write, when the number of bytes to be retrieved is truncated to the upper limit by fc->max_pages and there is an offset, the OOB is triggered.
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Description OSIDB Bzimport 2025-09-23 07:02:00 UTC 
In the Linux kernel, the following vulnerability has been resolved:

fuse: Block access to folio overlimit

syz reported a slab-out-of-bounds Write in fuse_dev_do_write.

When the number of bytes to be retrieved is truncated to the upper limit
by fc->max_pages and there is an offset, the oob is triggered.

Add a loop termination condition to prevent overruns.
Comment 1 Jon Moroney 2025-09-23 17:18:31 UTC 
Upstream advisory:
https://lore.kernel.org/linux-cve-announce/2025092303-CVE-2025-39888-3c85@gregkh/T