CVE-2026-68092 Overview
CVE-2026-68092 affects the Linux kernel timekeeping subsystem. The issue involves the jiffies clocksource being used during early boot before it is registered. This leaves the max_delta_raw field at zero, causing clocksource reads to be clamped to a maximum delta of zero. As a result, time fails to make progress during early boot. The condition was surfaced by a XEN Hardware Virtual Machine (HVM) exhibiting a long boot delay, and was bisected to recent enhancements in negative motion detection. The fix ensures the jiffies clocksource is initialized before its first usage in timekeeping_init().
Critical Impact
Boot-time timekeeping stall producing prolonged system boot delays, most visibly on XEN HVM guests running affected Linux kernel builds.
Affected Products
- Linux kernel builds containing the negative motion detection changes prior to the referenced fix commits
- XEN HVM guest environments running affected kernels
- Distributions shipping the pre-fix time/jiffies code path
Discovery Timeline
- 2026-08-10 - CVE-2026-68092 published to NVD
- 2026-08-10 - Last updated in NVD database
Technical Details for CVE-2026-68092
Vulnerability Analysis
The Linux kernel maintains a jiffies clocksource used for timekeeping when hardware clocksources are unavailable or before they are activated. Recent changes introduced negative motion detection, which relies on max_delta_raw to bound clocksource reads. Clocksources populate max_delta_raw during registration.
The kernel referenced the jiffies clocksource from early boot code paths before the registration routine ran. Because registration had not occurred, max_delta_raw remained zero. Every read of the clocksource was clamped to that zero delta, so the monotonic time value did not advance. Callers spinning on time progression during timekeeping_init() observed extended stalls, presenting as slow boot on XEN HVM guests. This is a kernel initialization ordering defect [CWE-665] rather than a memory-safety or privilege issue.
Root Cause
The root cause is an initialization order defect in the timekeeping subsystem. The jiffies clocksource was consumed before clocksource_register populated its delta bounds. The negative motion detection logic treats an uninitialized max_delta_raw value as a legitimate clamp of zero, which halts perceived time progression until registration occurs.
Attack Vector
No remote or local attacker interaction is required to trigger this condition. The behavior manifests deterministically during boot on affected kernels, particularly under the XEN HVM hypervisor. The CVE record does not describe an exploitation primitive; the practical impact is availability degradation via delayed boot. Publicly available scoring shows an EPSS value of 0.168% at the 6.43 percentile, consistent with low exploitation interest.
Refer to the upstream commits for the exact code changes: Kernel Git Commit 75b4780, Kernel Git Commit cd25e98, Kernel Git Commit f24df84, and Kernel Git Commit fe9bdea.
Detection Methods for CVE-2026-68092
Indicators of Compromise
- Extended boot times on XEN HVM guests running kernels that include the negative motion detection changes without the time/jiffies fix.
- Kernel log gaps or stalled timestamps prior to the completion of timekeeping_init().
- dmesg output showing delayed transitions between early boot messages that normally occur within milliseconds.
Detection Strategies
- Inventory running kernel versions across virtualized fleets and compare them against the fix commits referenced in the upstream advisory.
- Correlate boot duration metrics from hypervisor telemetry with kernel build identifiers to isolate affected images.
- Audit distribution changelogs to confirm whether backports of the jiffies registration fix are included.
Monitoring Recommendations
- Track boot-time regressions in continuous integration pipelines that build custom kernels.
- Alert on XEN HVM guests whose systemd-analyze boot time exceeds established baselines.
- Ingest kernel version and boot metrics into a centralized logging platform for longitudinal comparison across the fleet.
How to Mitigate CVE-2026-68092
Immediate Actions Required
- Apply the upstream Linux kernel patches that register the jiffies clocksource before its first use in timekeeping_init().
- Rebuild and redeploy affected XEN HVM guest images once the fix is present in the kernel tree.
- Roll back to a pre-regression kernel where operational schedules do not permit immediate patching.
Patch Information
The fix is delivered through the following stable kernel commits: Kernel Git Commit 75b4780, Kernel Git Commit cd25e98, Kernel Git Commit f24df84, and Kernel Git Commit fe9bdea. Consume the fix through your distribution's kernel updates or by cherry-picking the commits into custom builds.
Workarounds
- Pin affected systems to a kernel version predating the negative motion detection changes until the fix can be deployed.
- Coordinate with the hypervisor operations team to schedule guest reboots after the corrected kernel is staged.
- Validate the fix in a non-production XEN HVM environment before rolling into production hosts.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
