CVE-2026-98126 smb/client: validate new EOF for zero range
A local attacker can bypass file size limits on CIFS mounts, potentially causing resource exhaustion 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-2026-98126?
CVE-2026-98126 is a medium-severity missing authorization 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 zero range
When FALLOC_FL_ZERO_RANGE is used without FALLOC_FL_KEEP_SIZE, smb3_zero_range() may extend EOF without checking RLIMIT_FSIZE, allowing the file to grow beyond the caller's file-size limit.
Fix this by calling inode_newsize_ok() before sending the zero-range request when the operation would extend EOF.
Reproducer, using a file on a CIFS mount:
bash -c ' FILE=/mnt/cifs/repro
trap "" SIGXFSZ ulimit -f 3072
truncate -s 2M "$FILE" fallocate --zero-range -o 0 -l 4M "$FILE" echo "fallocate rc=$?" stat -c "file size=%s" "$FILE" '
Before this change, the operation succeeds despite the 3 MiB limit:
fallocate rc=0 file size=4194304
After this change, fallocate fails and leaves the file at 2 MiB.
Weakness: CWE-770
Which versions are affected by CVE-2026-98126?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-98126?
Apply the vendor's patch.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-98126 being exploited?
There is no known exploitation of CVE-2026-98126 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-104511, BELL-CVE-2026-98126, DEBIAN-CVE-2026-98126, GHSA-788x-356f-432m, UBUNTU-CVE-2026-98126.