CVE-2025-38509: 
Linux Ubuntu vulnerability analysis and mitigation

A vulnerability in the Linux kernel's WiFi implementation (mac80211) has been identified where VHT operating mode notifications for unsupported channel widths are not properly handled. The vulnerability was discovered and reported by syzbot, with initial disclosure on August 16, 2025 (NVD).

The vulnerability relates to VHT operating mode notifications for channel widths below 20 MHz, specifically 5 MHz and 10 MHz, which are not valid under the VHT specification. Without proper validation, malformed notifications using these unsupported widths could reach the ieee80211chanwidthtorxbw() function, triggering a WARNON condition due to invalid input (NVD, Debian Tracker).

The vulnerability could lead to system warnings and potential stability issues when processing invalid VHT operating mode notifications in the Linux kernel's WiFi stack. The accepted channel widths should include only 20, 40, 80, 160, and 80+80 MHz, which are valid for VHT operations (NVD).

The issue has been resolved by implementing early rejection of unsupported widths in the stalinkapplyparameters() function when opmodenotif is used. Fixed versions are available in various Linux distributions including Debian Bullseye (5.10.237-1), Bookworm (6.1.147-1), and Trixie (6.12.41-1) (Debian Tracker).