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

How to Fix CVE-2026-31734: sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU

By Sai Kiran Pandrala

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

Last verified: 2026-05-25

CVE-2026-31734 is a sched_ext: fix is_bpf_migration_disabled() false negative on non-preempt_rcu in Linux Linux. Fix it by upgrading to 6.18.22, 6.19.12, 7.0.

⚡ At a glance
SeverityNot verified - see official advisory
Actively exploited?Not currently in the CISA KEV catalog
AffectedLinux 8e4f0b1ebcf2180ab594f204f01279a666dadf3b up to (excluding) 72c43eb2e334febe93018cfb68ae828f55c6e49e; Linux 8e4f0b1ebcf2180ab594f204f01279a666dadf3b up to (excluding) b4992a9446bb9a639007bfd32bf5c5a7e30199e5; Linux 8e4f0b1ebcf2180ab594f204f01279a666dadf3b up to (excluding) 0c4a59df370bea245695c00aaae6ae75747139bd; Linux 6.18
Fixed in6.18.22, 6.19.12, 7.0
Type (CWE)Not verified

What is CVE-2026-31734?

CVE-2026-31734 is a sched_ext: fix is_bpf_migration_disabled() false negative on non-preempt_rcu flaw in Linux Linux. The vendor has not published a verified CVSS metric at the time of writing. 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:

sched_ext: Fix is_bpf_migration_disabled() false negative on non-PREEMPT_RCU

Since commit 8e4f0b1ebcf2 ("bpf: use rcu_read_lock_dont_migrate() for

trampoline.c"), the BPF prolog (__bpf_prog_enter) calls migrate_disable()

only when CONFIG_PREEMPT_RCU is enabled, via rcu_read_lock_dont_migrate().

Without CONFIG_PREEMPT_RCU, the prolog never touches migration_disabled,

so migration_disabled == 1 always means the task is truly

migration-disabled regardless of whether it is the current task.

The old unconditional p == current check was a false negative in this

case, potentially allowing a migration-disabled task to be dispatched to

a remote CPU and triggering scx_error in task_can_run_on_remote_rq().

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-2026-31734

Apply the vendor patch. Target the build named in the Fixed in row above (6.18.22, 6.19.12, 7.0). 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 6.18.22, 6.19.12, 7.0.

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-2026-31734 being exploited in the wild?

As of 2026-05-25, CVE-2026-31734 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-2026-31734?

A verified CVSS score is not listed in the public record for CVE-2026-31734. Check the vendor advisory and the NVD page for an updated metric.

What version fixes this?

Upgrade to 6.18.22, 6.19.12, 7.0.

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.*