CVE-2026-98127 smb/client: validate new EOF for insert range

Medium 5.5 Published 25 Sep 2026 Updated 21 Oct 2026

A local attacker can bypass file size limits in the Linux kernel SMB client via integer overflow, potentially causing denial of service or privilege escalation.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-98127?

CVE-2026-98127 is a medium-severity vulnerability in Linux kernel, published on 25 Sep 2026. 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:

smb/client: validate new EOF for insert range

smb3_insert_range() does not check if the new file size (i_size + len) is valid. This allows FALLOC_FL_INSERT_RANGE to bypass RLIMIT_FSIZE, exceed s_maxbytes, or produce a size outside the loff_t range.

Use check_add_overflow() to calculate the new EOF. Validate it with inode_newsize_ok() before modifying the file.

Reproducer, using a file on a CIFS mount:

bash -c ' FILE=/mnt/cifs/repro

trap "" SIGXFSZ ulimit -f 3072 # RLIMIT_FSIZE = 3 MiB

# A regular write is stopped at 3 MiB. dd if=/dev/zero of="$FILE" bs=1M count=4 status=none stat -c "size after write: %s" "$FILE"

# Insert 2 MiB into a 2 MiB file. truncate -s 2M "$FILE" fallocate -i -o 0 -l 2M "$FILE" stat -c "size after insert: %s" "$FILE" '

Before this change, the regular write stops at the 3 MiB limit, but insert range grows the file to 4 MiB:

dd: error writing '/mnt/cifs/repro': File too large size after write: 3145728 size after insert: 4194304

After this change, insert range also fails at the limit and leaves the 2 MiB file unchanged:

dd: error writing '/mnt/cifs/repro': File too large size after write: 3145728 fallocate: fallocate failed: File too large size after insert: 2097152

Weakness: CWE-190

Which versions are affected by CVE-2026-98127?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-98127?

Apply the vendor's patch.

Is CVE-2026-98127 being exploited?

There is no known exploitation of CVE-2026-98127 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as AZL-104253, BELL-CVE-2026-98127, DEBIAN-CVE-2026-98127, GHSA-5w48-8xg9-2grf, UBUNTU-CVE-2026-98127.