CVE-2026-64125 in Linux
Summary
by MITRE • 07/19/2026
In the Linux kernel, the following vulnerability has been resolved:
net: bcmgenet: keep RBUF EEE/PM disabled
Setting RBUF_EEE_EN | RBUF_PM_EN in RBUF_ENERGY_CTRL breaks the RX path on GENET hardware once MAC EEE becomes active. RX traffic stops flowing while the link stays up and the usual descriptor/RX error counters remain quiet. In that state the MAC still accepts frames (rbuf_ovflow_cnt keeps climbing) but RBUF no longer forwards them to DMA, so rx_packets is no longer incremented at the netdev level. On some boards the corruption ends up as a paging fault in skb_release_data via bcmgenet_rx_poll on an LPI exit.
Reproduced on Pi 4B (BCM2711 + BCM54213PE) and confirmed by Florian Fainelli on an internal Broadcom 4908-family board with the same crash signature. RBUF_PM_EN is not publicly documented.
This shows up more often now that phy_support_eee() enables EEE by default, but it also affects older kernels as soon as TX LPI is turned on via ethtool, so it is not specific to recent changes.
Always clear RBUF_EEE_EN | RBUF_PM_EN in bcmgenet_eee_enable_set so the bits stay off across resets. UMAC and TBUF setup is left alone so TX-side EEE keeps working.
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Analysis
by VulDB Data Team • 07/20/2026
The vulnerability described represents a critical networking flaw in the Linux kernel's bcmgenet driver affecting Broadcom GENET hardware platforms. This issue manifests as a complete breakdown in receive packet processing when certain energy efficiency features are enabled, creating a scenario where network traffic appears to be flowing normally while simultaneously being dropped at the hardware level. The problem specifically impacts devices using BCM2711 (Raspberry Pi 4B) and Broadcom 4908-family chipsets, with the vulnerability being reproducible across different hardware configurations sharing the same underlying architecture.
The technical root cause involves the improper handling of energy efficiency control registers within the bcmgenet driver. When RBUF_EEE_EN and RBUF_PM_EN bits are set in the RBUF_ENERGY_CTRL register, they conflict with the MAC EEE (Energy Efficient Ethernet) functionality, creating a state where the Receive Buffer (RBUF) stops forwarding packets to the DMA engine even though the physical link remains operational. This creates a silent network failure condition where incoming frames accumulate in the receive buffer causing overflow counters to increment while the actual packet count metrics at the network device level remain static, effectively masking the issue from standard monitoring systems.
The operational impact of this vulnerability is severe as it results in complete packet loss during active network sessions without any visible error indicators or system warnings. Network administrators would observe normal link status but experience intermittent connectivity issues where packets appear to be received by the hardware but never make it to the network stack for processing. This condition is particularly dangerous in production environments where network reliability is critical, as the issue can persist undetected for extended periods while silently degrading network performance and application availability.
The vulnerability specifically affects systems where EEE is enabled either through default kernel configuration or manual activation via ethtool commands targeting TX LPI states. The issue demonstrates a fundamental design flaw in register management within the bcmgenet driver where the RBUF energy efficiency controls are not properly maintained across hardware resets, leading to persistent corruption of the receive path functionality. This behavior was exacerbated by recent changes that enabled phy_support_eee() by default but the vulnerability existed in older kernels as well when TX LPI was manually activated.
The recommended mitigation strategy involves modifying the bcmgenet_eee_enable_set function to always clear the RBUF_EEE_EN and RBUF_PM_EN bits, ensuring these problematic control flags remain disabled across all system states and hardware resets. This approach preserves the existing TX-side EEE functionality through UMAC and TBUF configuration while preventing the conflict that causes the receive path failure. The solution specifically targets the register management aspect without affecting the broader energy efficiency capabilities of the network interface.
This vulnerability aligns with CWE-691, which addresses inadequate control of energy efficiency features in hardware drivers, and maps to ATT&CK technique T1486 related to data manipulation through network infrastructure. The issue represents a classic case of register state management failure where improper initialization or persistence of hardware control bits leads to system-level functionality degradation rather than simple error conditions. The fact that this affects both modern and legacy kernels demonstrates the persistent nature of hardware driver register management issues and highlights the importance of proper state preservation across system resets in embedded networking solutions.
The crash signature observed on LPI exit events, specifically resulting in paging faults within skb_release_data via bcmgenet_rx_poll, indicates that the underlying memory management structures become corrupted when the receive buffer attempts to process packets under these conflicting energy efficiency states. This corruption path through the network stack demonstrates how hardware-level register conflicts can propagate through multiple system layers, ultimately manifesting as kernel memory management failures rather than simple network connectivity issues. The absence of public documentation for RBUF_PM_EN further emphasizes the hidden complexity of modern networking hardware control registers and the challenges faced by open source driver developers in maintaining compatibility across diverse hardware implementations.
This vulnerability represents a significant concern for embedded systems and single-board computers where energy efficiency features are commonly enabled to reduce power consumption, particularly in IoT deployments and edge computing scenarios where reliable network connectivity is essential. The remediation approach of clearing these bits during EEE enable operations provides a targeted fix that maintains the intended energy efficiency benefits while eliminating the dangerous conflict that renders network interfaces effectively unusable under certain operating conditions.