CVE-2026-93830
HighCVSS 7.5Exploitation Probability (EPSS)
Low risk34th percentile - higher than 34% of all known CVEs
Summary
In the Linux kernel's stmmac network subsystem for XGMAC2, the RBUE (RX Buffer Unavailable) interrupt was enabled by default, causing a MAC interrupt storm under heavy RX load. The fix disables RBUE in the default interrupt mask because it is redundant—the normal RIE interrupt already triggers NAPI and refills descriptors. This prevents the storm while maintaining normal RX handling.
Risk Assessment
The risk is a potential MAC interrupt storm (observed ~695x more interrupts than actual RX completions), which can lead to high CPU usage, network performance degradation, and in extreme cases, stalled RX processing (DMA hang) with no forward progress.
Recommendation
Update the Linux kernel to a version containing this fix (commit removing RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX) as soon as possible. After updating, monitor the rx_buf_unav_irq counter (will always read 0 on XGMAC2) and verify network stability under heavy load.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: net: stmmac: xgmac2: disable RBUE in default RX interrupt mask Enabling the RX Buffer Unavailable (RBUE) interrupt is counterproductive and can trigger a MAC interrupt storm under heavy RX pressure. When the DMA runs out of RX descriptors it fires RBUE continuously until software refills the ring. However, RBUE is redundant: the normal RX completion interrupt (RIE) already triggers NAPI, which processes completed descriptors and refills the ring, causing the DMA to resume. The RBUE handler itself only sets handle_rx - the same outcome as RIE. On Agilex5 under heavy RX pressure, the MAC interrupt (which includes RBUE) was observed firing 1,821,811,555 times against only 2,618,627 actual RX completions - a ~695x ratio - confirming the severity of the storm. RBUE does not provide OOM recovery. If page_pool is exhausted, stmmac_rx_refill() cannot advance the DMA tail pointer, the DMA stays suspended, and RBUE fires again on the next NAPI completion - a storm with no forward progress. This patch trades that storm for a clean stall with the same RX outcome. Proper OOM recovery is a pre-existing gap outside the scope of this fix. Note: as a consequence of disabling RBUE, the rx_buf_unav_irq ethtool counter will always read 0 on XGMAC2 devices. This behaviour is already inconsistent across DWMAC core versions. Remove RBUE from XGMAC_DMA_INT_DEFAULT_EN and XGMAC_DMA_INT_DEFAULT_RX to prevent the interrupt storm while keeping normal RX handling intact.
Vulnerability data from NVD (NIST) · CISA KEV · EPSS