CVE-2023-54306

What it actually does

The Linux kernel TLS transmit path acquires tx_lock and may sleep uninterruptibly while waiting for TCP send window space; an adversarial peer that holds RWIN at zero indefinitely prevents forward progress, causing the holder task to remain asleep for extended periods and potentially triggering hung-task reports.

Why it matters to the business

Network-intensive workloads on affected Linux systems can experience prolonged stalls or complete unresponsiveness in TLS-protected connections, leading to service degradation, delayed operations, and the need for manual intervention or reboots.

How an attack unfolds

An attacker establishes a TLS connection and deliberately advertises a zero receive window for a prolonged duration; any kernel thread that subsequently acquires the TLS tx_lock and attempts to transmit will block without progress, leaving the lock held and starving other operations that require the same lock.

How to fix it

Upgrade to a kernel containing commit bde541a57b4204d0a800afbbd3d1c06c9cdb133f or later; apply the vendor-supplied stable update that replaces uninterruptible sleeps with interruptible ones and reschedules work when the lock cannot be acquired.

How to confirm the fix worked

Confirm the running kernel Git commit or package version includes bde541a57b4204d0a800afbbd3d1c06c9cdb133f; re-run the existing TLS selftest and verify no hung-task reports occur under sustained zero-window conditions.

Typical attack path

1. Establish a TCP/TLS session to the target
2. Advertise a persistent zero receive window
3. Trigger kernel TLS transmit path on the victim
4. Observe task hang and lock contention

How to detect it

Review kernel logs for hung-task warnings mentioning tls or tx_lock; correlate with TLS connection establishment events and look for repeated zero-window TCP segments from external peers.

What your security team should do

• Prioritize patching all Linux systems that perform TLS offload or terminate TLS connections
• Monitor for hung-task kernel messages related to tls_tx
• Apply the fixed commit or distribution kernel update within standard change windows given the low but non-zero EPSS