CVE-2026-99017 Linux CVE debrief

Who should care

Defenders responsible for Linux systems, especially those with T-Head C9xx CPUs, should assess exposure and verify the vulnerability status of their systems. Operators and security teams must prioritize verifying the vulnerability status of Linux systems with T-Head C9xx CPUs and ensure that the mitigation is applied by enabling CONFIG_RISCV_ALTERNATIVE_EARLY. Vulnerability management teams should review compensating controls for exposed systems while and

Why it matters

A vulnerability in the Linux kernel's RISC-V errata handling requires verification of vulnerability status and mitigation application for Linux systems with T-Head C9xx CPUs.

• Verification of vulnerability status for Linux systems with T-Head C9xx CPUs is required
• Enabling CONFIG_RISCV_ALTERNATIVE_EARLY is necessary to apply the mitigation
• Monitoring sysfs reports for vulnerability status is necessary

Technical summary

The Linux kernel's RISC-V errata handling has a vulnerability where the errata_probe_ghostwrite() function only marks the CPU as vulnerable when called during the RISCV_ALTERNATIVES_EARLY_BOOT stage. The mitigation in ghostwrite_enable_mitigation() only takes effect if the vulnerable state was recorded before boot alternatives are patched. This issue arises when CONFIG_RISCV_ALTERNATIVE_EARLY is not enabled, causing ghostwrite_state to never be set to VULNERABLE. As a result, ghostwrite_enable_mitigation() returns false, xtheadvector remains enabled, and sysfs reports 'Not affected' on a vulnerable T-Head C9xx CPU. The vulnerability requires verification of vulnerability status and mitigation application for A

Defensive priority

Defenders should prioritize verifying the vulnerability status of Linux systems, especially those with T-Head C9xx CPUs, and ensure that the mitigation is applied by enabling CONFIG_RISCV_ALTERNATIVE_EARLY.

Recommended defensive actions

• Verify the vulnerability status of Linux systems, especially those with T-Head C9xx CPUs
• Enable CONFIG_RISCV_ALTERNATIVE_EARLY to apply the mitigation
• Monitor sysfs reports for vulnerability status
• 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
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up

Evidence notes

The CVE record and source item provide details on the vulnerability and its mitigation. However, the corpus does not establish versions, exploitation, impact, or remediation beyond enabling CONFIG_RISCV_ALTERNATIVE_EARLY.

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.