CVE-2025-38691 pNFS: Fix uninited ptr deref in block/scsi layout

What is CVE-2025-38691?

CVE-2025-38691 is a medium-severity vulnerability in Debian Debian Linux, published on 4 Sep 2025. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

pNFS: Fix uninited ptr deref in block/scsi layout

The error occurs on the third attempt to encode extents. When function ext_tree_prepare_commit() reallocates a larger buffer to retry encoding extents, the "layoutupdate_pages" page array is initialized only after the retry loop. But ext_tree_free_commitdata() is called on every iteration and tries to put pages in the array, thus dereferencing uninitialized pointers.

An additional problem is that there is no limit on the maximum possible buffer_size. When there are too many extents, the client may create a layoutcommit that is larger than the maximum possible RPC size accepted by the server.

During testing, we observed two typical scenarios. First, one memory page for extents is enough when we work with small files, append data to the end of the file, or preallocate extents before writing. But when we fill a new large file without preallocating, the number of extents can be huge, and counting the number of written extents in ext_tree_encode_commit() does not help much. Since this number increases even more between unlocking and locking of ext_tree, the reallocated buffer may not be large enough again and again.

Weakness: CWE-908

Which versions are affected by CVE-2025-38691?

It affects 2 products.

Products include Debian Debian Linux, Linux kernel.

How do I fix CVE-2025-38691?

Apply the vendor's patch.

Is CVE-2025-38691 being exploited?

There is no known exploitation of CVE-2025-38691 in the wild and no public exploit code.

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Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as AZL-66800, AZL-73920, BELL-CVE-2025-38691, DEBIAN-CVE-2025-38691, GHSA-94hx-q75x-2q84, ROOT-OS-DEBIAN-11-CVE-2025-38691 and 4 more.