CVE-2025-21704usb: cdc-acm: Check control transfer buffer size before access

Official description

In the Linux kernel, the following vulnerability has been resolved: usb: cdc-acm: Check control transfer buffer size before access If the first fragment is shorter than struct usb_cdc_notification, we can't calculate an expected_size. Log an error and discard the notification instead of reading lengths from memory outside the received data, which can lead to memory corruption when the expected_size decreases between fragments, causing `expected_size - acm->nb_index` to wrap. This issue has been present since the beginning of git history; however, it only leads to memory corruption since commit ea2583529cd1 ("cdc-acm: reassemble fragmented notifications"). A mitigating factor is that acm_ctrl_irq() can only execute after userspace has opened /dev/ttyACM*; but if ModemManager is running, ModemManager will do that automatically depending on the USB device's vendor/product IDs and its other interfaces.

Affected packages & fixed versions

Affected products (as reported)

References

• https://git.kernel.org/stable/c/a4e1ae5c0533964170197e4fb4f33bc8c1db5cd2
• https://git.kernel.org/stable/c/90dd2f1b7342b9a671a5ea4160f408037b92b118
• https://git.kernel.org/stable/c/871619c2b78fdfe05afb4e8ba548678687beb812
• https://git.kernel.org/stable/c/7828e9363ac4d23b02419bf2a45b9f1d9fb35646
• https://git.kernel.org/stable/c/6abb510251e75f875797d8983a830e6731fa281c
• https://git.kernel.org/stable/c/f64079bef6a8a7823358c3f352ea29a617844636
• https://git.kernel.org/stable/c/383d516a0ebc8641372b521c8cb717f0f1834831
• https://git.kernel.org/stable/c/e563b01208f4d1f609bcab13333b6c0e24ce6a01
• https://project-zero.issues.chromium.org/issues/395107243
• https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
• https://lists.debian.org/debian-lts-announce/2025/03/msg00028.html
• https://cert-portal.siemens.com/productcert/html/ssa-265688.html
• https://cert-portal.siemens.com/productcert/html/ssa-784472.html