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CVE-2025-40071: tty: n_gsm: Don't block input queue by waiting MSC

• Severity: unknown
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.2% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2025-10-28 · updated 2026-10-30

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.

Affected products

• Linux: from 5.15.54 before 5.16; from 5.17.6 before 5.18 — fixed in 5.16, 5.18

How to fix

Upgrade to a fixed version: Linux 5.16, 5.18. Check the vendor advisory for mitigations.

References

• https://git.kernel.org/stable/c/3cf0b3c243e56bc43be560617416c1d9f301f44c
• https://git.kernel.org/stable/c/5416e89b81b00443cb03c88df8da097ae091a141
• https://git.kernel.org/stable/c/8fcc22d6b90304d8b7436e101562218ea3faf73b
• https://git.kernel.org/stable/c/c36785f9de03df56ff9b8eca30fa681a12b2310d
• https://git.kernel.org/stable/c/c5a2791a7f11939f05f95c01f0aec0c55bbf28d5

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