⚠ 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-2026-31705: ksmbd: fix out-of-bounds write 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-2026-31705 is a ksmbd: fix out-of-bounds write in Linux Linux. Fix it by upgrading to 6.6.136, 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 e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to (excluding) ffbce350c6fd1e99116ea57383b9031717e36d3b; Linux e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to (excluding) 98f3de6ef4efbd899348d333f0902dc4ff14380c; Linux e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to (excluding) 790304c02bf9bd7b8171feda4294d6e62d32ae8f; Linux e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to (excluding) 922d48fe8c19f388ffa2f709f33acaae4e408de2; Linux e2b76ab8b5c9327ab2dae6da05d0752eb2f4771d up to (excluding) 30010c952077a1c89ecdd71fc4d574c75a8f5617; Linux f2283680a80571ca82d710bc6ecd8f8beac67d63
Fixed in6.6.136, 6.12.84, 6.18.25, 7.0.2, 7.1-rc1
Type (CWE)Not verified

What is CVE-2026-31705?

CVE-2026-31705 is a ksmbd: fix out-of-bounds write 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 out-of-bounds write in smb2_get_ea() EA alignment

smb2_get_ea() applies 4-byte alignment padding via memset() after

writing each EA entry. The bounds check on buf_free_len is performed

before the value memcpy, but the alignment memset fires unconditionally

afterward with no check on remaining space.

When the EA value exactly fills the remaining buffer (buf_free_len == 0

after value subtraction), the alignment memset writes 1-3 NUL bytes

past the buf_free_len boundary. In compound requests where the response

buffer is shared across commands, the first command (e.g., READ) can

consume most of the buffer, leaving a tight remainder for the QUERY_INFO

EA response. The alignment memset then overwrites past the physical

kvmalloc allocation into adjacent kernel heap memory.

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-2026-31705

Apply the vendor patch. Target the build named in the Fixed in row above (6.6.136, 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 6.6.136, 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-2026-31705 being exploited in the wild?

As of 2026-05-25, CVE-2026-31705 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-2026-31705?

The CVSS base score is 9.8 (Critical).

What version fixes this?

Upgrade to 6.6.136, 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.*