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How the CVE Works:
In SEV-SNP (Secure Encrypted Virtualization – Secure Nested Paging) virtual machines, the hypervisor provides a nominal TSC (Time Stamp Counter) frequency via the GUEST_TSC_FREQ MSR (Model Specific Register). However, the actual mean TSC frequency programmed into the hardware during the VM launch can deviate slightly (~0.2%) from this reported nominal value. The Linux guest kernel, relying solely on the nominal frequency for its timekeeping calculations, experiences a gradual clock skew against the hypervisor over extended VM uptime. This discrepancy causes the guest’s high-resolution timers (hrtimers) to fire earlier than intended from the guest’s perspective, as its internal timekeeping is slightly slower than the actual hardware clock. The fix involves using a precise `TSC_FACTOR` from the SEV secrets page instead of the inaccurate nominal frequency.
DailyCVE Form:
Platform: Linux Kernel
Version: x86/sev
Vulnerability: Clock Skew
Severity: Medium
Date: 08/16/2025
Prediction: Patch expected by 08/30/2025
What Undercode Say:
`rdmsr GUEST_TSC_FREQ`
`snoboot –secrets-page`
`early_ioremap_encrypted()`
`cat /sys/kernel/debug/tsc_frequency`
How Exploit:
Exploitation is not direct. An attacker cannot trigger this; it is a system reliability flaw. The skew accumulates over time, potentially causing premature timer interrupts that could disrupt time-sensitive applications or scheduled tasks within the guest VM, leading to performance degradation or instability.
Protection from this CVE
Apply kernel patch.
Update to fixed kernel.
Use TSC_FACTOR.
Impact:
Guest timer inaccuracies.
System performance degradation.
Potential application disruption.
🎯Let’s Practice Exploiting & Learn Patching For Free:
Sources:
Reported By: nvd.nist.gov
Extra Source Hub:
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