CVE-2026-89603 Linux CVE debrief

Who should care

Linux kernel developers, administrators, and users who rely on seccomp for system call filtering should assess their exposure and verify the installation of seccomp filters. This includes those responsible for maintaining and securing Linux-based systems, as well as developers who work with the Linux kernel. Additionally, security teams and vulnerability management teams should be aware of this vulnerability and its potential impacts on their systems.

Why it matters

A Linux kernel vulnerability allows an unprivileged process to bypass seccomp filters, potentially enabling prohibited system calls. Linux kernel developers, administrators, and users relying on seccomp should assess exposure and verify filter installations.

• Unprivileged process may execute prohibited system calls
• Seccomp filter bypass possible via TSYNC flag
• System call filtering may not work as intended
• Verification of seccomp filter installations required

Technical summary

The Linux kernel's entry code has a vulnerability that allows an unprivileged process to bypass a seccomp filter installed by another thread via the SECCOMP_FILTER_FLAG_TSYNC flag. This occurs when a thread is stopped in syscall_trace_enter() for ptrace, and another thread installs a seccomp filter with the TSYNC flag. The filter is silently bypassed due to a cached 'work' variable sampled on entry.

Defensive priority

Medium

Recommended defensive actions

• Review Linux kernel versions and configurations for exposure
• Verify seccomp filter installations and configurations
• Monitor system calls for unusual activity
• Apply kernel patches if available
• Track exceptions and retest remediated assets
• Check relevant monitoring, detection, and logs for exposed assets
• Confirm whether affected product deployments exist in managed environments

Evidence notes

The CVE record and NVD entry provide details about the vulnerability, but the scope of affected systems and versions is not explicitly stated. The Linux kernel patch references suggest specific commits that 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.