CVE-2021-47137

What it actually does

Invalid address programmed into RX descriptor on memory allocation or DMA mapping failure, leading to memory corruption in the network driver RX ring.

Why it matters to the business

Potential system instability, crashes, or data corruption during network operations on affected systems; low exploitation likelihood reduces immediate operational risk despite widespread Linux kernel use.

How an attack unfolds

An attacker triggers repeated network traffic that causes memory allocation or DMA mapping failures in the lantiq driver RX path, resulting in an invalid descriptor being used and subsequent memory corruption.

How to fix it

Update affected systems to the fixed version firefox 91.9.1-1.el8_6.alma or later; in kernel terms, ensure the driver reuses the previous skb and mapping on allocation failure while incrementing the rx drop counter.

How to confirm the fix worked

Verify package version matches or exceeds the fixed release; test RX path under simulated allocation failure conditions to confirm no invalid descriptors are programmed.

Typical attack path

1. Send crafted or high-volume network packets to the target interface
2. Force memory allocation or DMA mapping failure in RX ring processing
3. Invalid address written to descriptor ring
4. Subsequent DMA operations cause memory corruption

How to detect it

Search kernel logs and network driver traces for RX ring allocation failures or unexpected memory corruption events around packet processing.

What your security team should do

• Apply the listed fixed package version across all affected AlmaLinux systems
• Monitor EPSS and KEV status for any future increase in exploit activity
• Review network driver logs for allocation failure events