CVE-2026-74656 Linux CVE debrief

Who should care

Linux kernel developers, administrators, and users of affected Linux kernel versions should be aware of this vulnerability and take steps to mitigate it by reviewing and applying patches provided by the Linux kernel maintainers and updating affected Linux kernel versions. Affected Linux kernel versions need to be updated with patches provided by the maintainers. Verification of Linux kernel versions and application of patches is necessary to prevent and

Why it matters

This vulnerability in the Linux kernel's IPv4 implementation could allow local attackers to escalate privileges or cause a denial-of-service condition. Affected Linux kernel versions need to be updated with patches provided by the maintainers.

• Local privilege escalation is possible if an attacker can trigger the use-after-free condition.
• Denial-of-service conditions may occur if an attacker can repeatedly trigger the vulnerability.
• Verification of Linux kernel versions and application of patches is necessary to prevent exploitation.
• Monitoring system logs for potential exploitation attempts is recommended.

Technical summary

The `fib_nhc_update_mtu()` function in the Linux kernel's IPv4 implementation is vulnerable to a use-after-free attack. This occurs when the function walks the nexthop exception table under RTNL, but RTNL does not serialize this walk with PMTU exception updates. An attacker could potentially exploit this vulnerability to escalate privileges or cause a denial-of-service condition. The vulnerability can be mitigated by reviewing and applying patches provided by the Linux kernel maintainers and updating affected Linux kernel versions.

Defensive priority

High

Recommended defensive actions

• Review and apply patches provided by the Linux kernel maintainers
• Update affected Linux kernel versions to ensure the fix is applied
• Monitor system logs for potential exploitation attempts
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed.

Evidence notes

The vulnerability was reported by an unnamed source and is described in the Linux kernel's official Git repository. The affected versions of the Linux kernel have been identified, and patches have been provided to address the issue.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.