CVE-2025-21708 is a vulnerability identified in the Linux kernel's USB network driver, specifically within the rtl8150 driver which supports certain USB Ethernet adapters. The issue arises from improper endpoint type checking during the submission of USB Request Blocks (URBs). Syzkaller, a kernel fuzzing tool, detected that the driver was submitting URBs with a pipe endpoint type that did not match the expected USB endpoint type, triggering warnings and potential instability. The root cause is the lack of basic endpoint validation for bulk and interrupt endpoints during URB submission, which can lead to unexpected behavior or kernel warnings. The patch introduced enables simple endpoint checking to ensure that the endpoint types used in URB submissions correspond correctly to the expected USB endpoint types, mitigating the issue. However, this fix is noted as untested on real hardware, indicating that further validation is needed. The vulnerability affects Linux kernel versions identified by a specific commit hash (1da177e4c3f41524e886b7f1b8a0c1fc7321cac2), and it is related to the rtl8150 USB network driver. No known exploits are reported in the wild, and no CVSS score has been assigned yet. The vulnerability primarily causes kernel warnings and potential instability rather than direct code execution or privilege escalation, but improper USB endpoint handling could theoretically be leveraged in complex attack scenarios involving USB devices.

For European organizations, the impact of CVE-2025-21708 depends largely on the deployment of Linux systems utilizing the rtl8150 USB Ethernet adapter driver. Since this vulnerability relates to USB network device handling, it could cause system instability, kernel warnings, or crashes when affected devices are connected or used. This could disrupt network connectivity on affected Linux hosts, impacting availability of services relying on these network interfaces. In environments with high reliance on Linux-based infrastructure, such as data centers, cloud providers, or industrial control systems, this could lead to operational disruptions. Although no direct remote code execution or privilege escalation has been demonstrated, the vulnerability could be exploited in targeted attacks involving malicious USB devices crafted to trigger the improper endpoint handling, potentially as part of a multi-stage attack. European organizations with strict uptime requirements or those operating critical infrastructure should be particularly cautious. Additionally, the vulnerability could complicate forensic analysis or incident response due to kernel warnings and instability. However, the lack of known exploits and the nature of the issue suggest the immediate risk is moderate but warrants timely patching to prevent potential escalation.

1. Apply the official Linux kernel patch that enables basic endpoint checking in the rtl8150 USB network driver as soon as it is available and verified on production hardware. 2. Conduct thorough testing of the patched kernel on representative hardware to ensure stability and compatibility before wide deployment. 3. Restrict the use of USB Ethernet adapters that rely on the rtl8150 driver in sensitive or critical environments until patches are applied. 4. Implement USB device control policies using endpoint security solutions or Linux USBGuard to limit unauthorized or untrusted USB devices, reducing the attack surface. 5. Monitor kernel logs for usb_submit_urb warnings or related messages that may indicate attempts to exploit this vulnerability or related USB endpoint issues. 6. Educate system administrators about the risks of connecting untrusted USB devices and enforce policies to prevent unauthorized device usage. 7. Maintain up-to-date Linux kernel versions and subscribe to security advisories to receive timely updates on this and related vulnerabilities.