⚠ Reference material — not professional advice. Test in staging, back up first, verify against your specific version. Use your own judgment for your environment.
● Critical · CVSS 9.8

How to Fix CVE-2026-31718: ksmbd: fix use-after-free in Linux

By Sai Kiran Pandrala

Other vulnerabilities in the same area that are worth patching alongside this one:

Last verified: 2026-05-25

CVE-2026-31718 is a ksmbd: fix use-after-free in Linux Linux. Fix it by upgrading to 6.6.140, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1.

⚡ At a glance
SeverityCVSS 9.8 - Critical
Actively exploited?Not currently in the CISA KEV catalog
AffectedLinux 8df4bcdb0a4232192b2445256c39b787d58ef14d up to (excluding) 0000a7780e0e446a28a273572f6ea8f7f582f694; Linux c8efcc786146a951091588e5fa7e3c754850cb3c up to (excluding) e33c65f011980b4ad4abfd93585ec2079856368f; Linux c8efcc786146a951091588e5fa7e3c754850cb3c up to (excluding) 3d6682726c2d3a46d31dae88b8166786b09b03ad; Linux c8efcc786146a951091588e5fa7e3c754850cb3c up to (excluding) b34fc42cfe922e551f7a27d3ac3bb016e41d7dd9; Linux c8efcc786146a951091588e5fa7e3c754850cb3c up to (excluding) 235e32320a470fcd3998fb3774f2290a0eb302a1; Linux 6.9
Fixed in6.6.140, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1
Type (CWE)Not verified

What is CVE-2026-31718?

CVE-2026-31718 is a ksmbd: fix use-after-free flaw in Linux Linux. It carries a CVSS base score of 9.8 (critical). It is not currently listed in the CISA Known Exploited Vulnerabilities catalog.

From the source record: In the Linux kernel, the following vulnerability has been resolved:

ksmbd: fix use-after-free in __ksmbd_close_fd() via durable scavenger

When a durable file handle survives session disconnect (TCP close without

SMB2_LOGOFF), session_fd_check() sets fp->conn = NULL to preserve the

handle for later reconnection. However, it did not clean up the byte-range

locks on fp->lock_list.

Later, when the durable scavenger thread times out and calls

__ksmbd_close_fd(NULL, fp), the lock cleanup loop did:

spin_lock(&fp->conn->llist_lock);

This caused a slab use-after-free because fp->conn was NULL and the

original connection object had already been freed by

ksmbd_tcp_disconnect().

The root cause is asymmetric cleanup: lock entries (smb_lock->clist) were

left dangling on the freed conn->lock_list while fp->conn was nulled out.

Why it matters in practice: The blast radius depends on how the affected service is exposed. An internet-facing instance with no compensating controls is the highest-risk configuration.

Am I affected?

You are affected if your installation of Linux matches a version listed in the Affected row above.


# Debian/Ubuntu
dpkg -s linux | grep Version
# RHEL/Rocky
rpm -q linux

How to fix CVE-2026-31718

Apply the vendor patch. Target the build named in the Fixed in row above (6.6.140, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1). The runnable command set below covers the most common deployment patterns for Linux.

Ubuntu / Debian


sudo apt-get update
sudo apt-get install --only-upgrade linux
dpkg -s linux | grep Version

RHEL / CentOS / Rocky


sudo dnf upgrade linux -y
rpm -q linux

After applying the patch

  1. Restart the service or device so the patched binary loads.
  2. Confirm the running version matches the Fixed in row using the verification command below.
  3. Rotate credentials and API keys that the affected service could access if the asset was exposed during the disclosure window.

If you can't patch immediately

Until the patch lands, narrow the attack surface with these runnable controls.

Restrict network exposure

Block public access to the affected service at the perimeter. Allow only trusted source IPs.


# Linux iptables: only allow trusted admin subnet
sudo iptables -A INPUT -p tcp --dport 443 -s 10.10.10.0/24 -j ACCEPT
sudo iptables -A INPUT -p tcp --dport 443 -j DROP
sudo iptables-save | sudo tee /etc/iptables/rules.v4


# Windows firewall: only allow trusted admin subnet on management port
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Allow" -Direction Inbound -Action Allow `
  -RemoteAddress 10.10.10.0/24 -Protocol TCP -LocalPort 443
New-NetFirewallRule -DisplayName "Restrict-Mgmt-Deny"  -Direction Inbound -Action Block `
  -Protocol TCP -LocalPort 443

Mitigations are temporary. Apply the vendor patch as soon as a maintenance window opens.

How to verify the fix worked

Confirm the patched build is the one actually running.


# Debian/Ubuntu
dpkg -s linux | grep Version
# RHEL/Rocky
rpm -q linux

Expected: a version at or above 6.6.140, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1.

Also worth doing: pull recent log windows for indicators of compromise listed in the vendor advisory, and re-run an authenticated vulnerability scan with up-to-date signatures.

Frequently asked questions

Is CVE-2026-31718 being exploited in the wild?

As of 2026-05-25, CVE-2026-31718 is not listed in the CISA Known Exploited Vulnerabilities catalog. Watch the catalog and patch on a normal cadence; KEV status can change as exploitation evidence emerges.

What is the CVSS score for CVE-2026-31718?

The CVSS base score is 9.8 (Critical).

What version fixes this?

Upgrade to 6.6.140, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1.

Will a WAF or IDS rule alone close this?

No. Network filters cut down opportunistic scans but they do not remove the flaw. The vendor patch is the only durable fix.

References

*Assembled from the official vendor advisory, the NVD record, and the CISA KEV listing on 2026-05-25. Always confirm against the vendor advisory before applying changes in production.*