Vulnerability Details CVE-2026-31437
In the Linux kernel, the following vulnerability has been resolved:
netfs: Fix NULL pointer dereference in netfs_unbuffered_write() on retry
When a write subrequest is marked NETFS_SREQ_NEED_RETRY, the retry path
in netfs_unbuffered_write() unconditionally calls stream->prepare_write()
without checking if it is NULL.
Filesystems such as 9P do not set the prepare_write operation, so
stream->prepare_write remains NULL. When get_user_pages() fails with
-EFAULT and the subrequest is flagged for retry, this results in a NULL
pointer dereference at fs/netfs/direct_write.c:189.
Fix this by mirroring the pattern already used in write_retry.c: if
stream->prepare_write is NULL, skip renegotiation and directly reissue
the subrequest via netfs_reissue_write(), which handles iterator reset,
IN_PROGRESS flag, stats update and reissue internally.
Exploit prediction scoring system (EPSS) score
EPSS Score 0.001
EPSS Ranking 2.2%
CVSS Severity
CVSS v3 Score 5.5
References
Products affected by CVE-2026-31437
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cpe:2.3:o:linux:linux_kernel:6.18.17
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cpe:2.3:o:linux:linux_kernel:6.18.18
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cpe:2.3:o:linux:linux_kernel:6.18.19
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cpe:2.3:o:linux:linux_kernel:6.18.20
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cpe:2.3:o:linux:linux_kernel:6.19.10
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cpe:2.3:o:linux:linux_kernel:6.19.7
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cpe:2.3:o:linux:linux_kernel:6.19.8
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cpe:2.3:o:linux:linux_kernel:6.19.9