CVE-2024-56739

What it actually does

If __rtc_read_time fails, rtc_timer_do_work may pass uninitialized or illegal rtc_time to rtc_tm_to_ktime, producing KTIME_MAX and causing periodic timers in the rtc timerqueue to continually expire and trigger kernel softlockup.

Why it matters to the business

Systems may experience repeated kernel softlockups leading to unresponsiveness or denial of service; low urgency given absence from KEV, stable low EPSS, and no ransomware association despite listed threat actor campaigns.

How an attack unfolds

An attacker with local access triggers conditions causing __rtc_read_time to fail (for example via hardware manipulation or error states), allowing uninitialized time values to reach the timer expiration logic and induce continuous softlockups; listed actors in 2024 zero-day and Linux kernel campaigns provide context but no public exploit maturity.

How to fix it

Apply the listed fixed versions for affected packages; for firefox on Ubuntu 14.04 LTS upgrade to 50.0+build2-0ubuntu0.14.04.2 or later equivalent kernel patches addressing the rtc timer handling.

How to confirm the fix worked

Confirm the installed package version matches or exceeds the fixed release, review kernel logs for absence of softlockup warnings related to rtc_timer_do_work, and test RTC read paths under error conditions.

Typical attack path

1. Obtain local access to the system
2. Induce failure in __rtc_read_time call
3. Allow rtc_tm_to_ktime to return KTIME_MAX
4. Trigger repeated expiration of timers in rtc->timerqueue
5. Cause kernel softlockup and system degradation

How to detect it

Review kernel logs for repeated softlockup messages tied to rtc timers or timerqueue activity; correlate with any recent RTC hardware errors or time-related kernel panics; threat actor mentions suggest watching for espionage or financially motivated access patterns preceding the issue.

What your security team should do

• Prioritize patching systems running the affected rtc timer code even with low EPSS
• Monitor for kernel softlockup reports in system logs
• Limit local access where feasible until upgrades are complete
• Track downstream dependents for broader ecosystem exposure