CVE-2025-40071 tty: n_gsm: Don't block input queue by waiting MSC
A local attacker can cause a denial of service in the Linux kernel by blocking the input queue during GSM modem status updates.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2025-40071?
CVE-2025-40071 is a denial of service vulnerability in Linux, published on 28 Oct 2025. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
tty: n_gsm: Don't block input queue by waiting MSC
Currently gsm_queue() processes incoming frames and when opening a DLC channel it calls gsm_dlci_open() which calls gsm_modem_update(). If basic mode is used it calls gsm_modem_upd_via_msc() and it cannot block the input queue by waiting the response to come into the same input queue.
Instead allow sending Modem Status Command without waiting for remote end to respond. Define a new function gsm_modem_send_initial_msc() for this purpose. As MSC is only valid for basic encoding, it does not do anything for advanced or when convergence layer type 2 is used.
Which versions are affected by CVE-2025-40071?
How do I fix CVE-2025-40071?
Apply the vendor's patch.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2025-40071 being exploited?
There is no known exploitation of CVE-2025-40071 in the wild and no public exploit code.
Sources
Also known as AZL-68942, BELL-CVE-2025-40071, DEBIAN-CVE-2025-40071, GHSA-xj3g-qjx7-6cfm, ROOT-OS-DEBIAN-12-CVE-2025-40071, ROOT-OS-DEBIAN-13-CVE-2025-40071 and 3 more.