CVE-2026-99018 Linux CVE debrief

Who should care

Linux kernel maintainers and users, RISC-V architecture users, security teams responsible for monitoring and patching Linux kernel vulnerabilities, and operators of affected systems should assess exposure and prioritize patching. This includes teams responsible for vulnerability management, incident response, and system administration.

Why it matters

A vulnerability in the Linux kernel's handling of the shadow call stack on RISC-V architectures has been addressed, allowing an attacker to control the pointer and potentially execute arbitrary code. Linux kernel maintainers and users, RISC-V architecture users, and security teams should assess exposure and prioritize patching.

• Potential for arbitrary code execution
• Elevation of privileges possible
• Increased risk of kernel compromise
• Need for urgent patching and verification

Technical summary

The Linux kernel's handling of the shadow call stack on RISC-V architectures was vulnerable to exploitation, allowing an attacker to control the shadow call stack pointer and potentially execute arbitrary code. The vulnerability is due to the kernel's `handle_exception` function not properly reloading the shadow call stack pointer when handling traps from userspace. The fix involves gating the shadow call stack reload on sstatus.SPP, not tp. This vulnerability could allow an attacker to gain control of the shadow call stack pointer, potentially leading to arbitrary code execution.

Defensive priority

High

Recommended defensive actions

• Review and apply the patches provided by the Linux kernel maintainers to address the vulnerability.
• Ensure that the Linux kernel is updated to a version that includes the fix.
• Monitor system logs for potential exploitation attempts.
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• Review compensating controls for exposed systems while remediation is scheduled and verified.
• 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.

Evidence notes

The CVE record and associated source item provide details on the vulnerability, including its impact on the Linux kernel's handling of the shadow call stack on RISC-V architectures. The vulnerability allows an attacker to control the shadow call stack pointer, potentially leading to arbitrary code execution. Evidence is based on the CVE record and associated source item. Defenders should verify the presence of affected systems and review the supplied official advisory or CVE record to validate affected scope, severity, and vendor.

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.