CVE-2023-53805 in Linux
Summary
by MITRE • 12/09/2025
In the Linux kernel, the following vulnerability has been resolved:
tty: n_gsm: fix UAF in gsm_cleanup_mux
In gsm_cleanup_mux() the 'gsm->dlci' pointer was not cleaned properly, leaving it a dangling pointer after gsm_dlci_release. This leads to use-after-free where 'gsm->dlci[0]' are freed and accessed
by the subsequent gsm_cleanup_mux().
Such is the case in the following call trace:
<TASK> __dump_stack lib/dump_stack.c:88 [inline]
dump_stack_lvl+0x1e3/0x2cb lib/dump_stack.c:106 print_address_description+0x63/0x3b0 mm/kasan/report.c:248 __kasan_report mm/kasan/report.c:434 [inline]
kasan_report+0x16b/0x1c0 mm/kasan/report.c:451 gsm_cleanup_mux+0x76a/0x850 drivers/tty/n_gsm.c:2397 gsm_config drivers/tty/n_gsm.c:2653 [inline]
gsmld_ioctl+0xaae/0x15b0 drivers/tty/n_gsm.c:2986 tty_ioctl+0x8ff/0xc50 drivers/tty/tty_io.c:2816 vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x61/0xcb </TASK>
Allocated by task 3501: kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track mm/kasan/common.c:46 [inline]
set_alloc_info mm/kasan/common.c:434 [inline]
____kasan_kmalloc+0xba/0xf0 mm/kasan/common.c:513 kasan_kmalloc include/linux/kasan.h:264 [inline]
kmem_cache_alloc_trace+0x143/0x290 mm/slub.c:3247 kmalloc include/linux/slab.h:591 [inline]
kzalloc include/linux/slab.h:721 [inline]
gsm_dlci_alloc+0x53/0x3a0 drivers/tty/n_gsm.c:1932 gsm_activate_mux+0x1c/0x330 drivers/tty/n_gsm.c:2438 gsm_config drivers/tty/n_gsm.c:2677 [inline]
gsmld_ioctl+0xd46/0x15b0 drivers/tty/n_gsm.c:2986 tty_ioctl+0x8ff/0xc50 drivers/tty/tty_io.c:2816 vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x61/0xcb
Freed by task 3501: kasan_save_stack mm/kasan/common.c:38 [inline]
kasan_set_track+0x4b/0x80 mm/kasan/common.c:46 kasan_set_free_info+0x1f/0x40 mm/kasan/generic.c:360 ____kasan_slab_free+0xd8/0x120 mm/kasan/common.c:366 kasan_slab_free include/linux/kasan.h:230 [inline]
slab_free_hook mm/slub.c:1705 [inline]
slab_free_freelist_hook+0xdd/0x160 mm/slub.c:1731 slab_free mm/slub.c:3499 [inline]
kfree+0xf1/0x270 mm/slub.c:4559 dlci_put drivers/tty/n_gsm.c:1988 [inline]
gsm_dlci_release drivers/tty/n_gsm.c:2021 [inline]
gsm_cleanup_mux+0x574/0x850 drivers/tty/n_gsm.c:2415 gsm_config drivers/tty/n_gsm.c:2653 [inline]
gsmld_ioctl+0xaae/0x15b0 drivers/tty/n_gsm.c:2986 tty_ioctl+0x8ff/0xc50 drivers/tty/tty_io.c:2816 vfs_ioctl fs/ioctl.c:51 [inline]
__do_sys_ioctl fs/ioctl.c:874 [inline]
__se_sys_ioctl+0xf1/0x160 fs/ioctl.c:860 do_syscall_x64 arch/x86/entry/common.c:50 [inline]
do_syscall_64+0x3d/0xb0 arch/x86/entry/common.c:80 entry_SYSCALL_64_after_hwframe+0x61/0xcb
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Analysis
by VulDB Data Team • 06/28/2026
The vulnerability described in the Linux kernel represents a use-after-free condition within the tty n_gsm driver, specifically in the gsm_cleanup_mux function. This flaw occurs when the gsm->dlci pointer is not properly cleared after the gsm_dlci_release operation, leaving it as a dangling pointer that can be accessed even after the memory has been freed. The issue manifests through a call trace showing memory access violations during ioctl operations on GSM line discipline devices, where the kernel's kasan (kernel address sanitizer) detects attempts to access freed memory locations.
The technical root cause stems from improper memory management in the GSM multiplexer cleanup routine. When gsm_dlci_release is called, it frees memory associated with dlci structures but fails to nullify the gsm->dlci pointer reference. Subsequently, when gsm_cleanup_mux executes, it attempts to access gsm->dlci[0] which points to already freed memory, triggering a use-after-free condition. This pattern violates fundamental memory safety principles and creates potential attack vectors for privilege escalation or system instability.
The operational impact of this vulnerability extends beyond simple memory corruption, as it can lead to system crashes, data corruption, or potentially arbitrary code execution in scenarios where attackers can control the ioctl operations on GSM devices. The vulnerability affects systems using the n_gsm tty driver for GSM modem communications and can be exploited through crafted ioctl calls that trigger the faulty cleanup path. This aligns with CWE-416, which describes use-after-free conditions, and represents a critical security concern within kernel space memory management.
Mitigation strategies include patching the kernel to ensure proper pointer nullification after memory release operations, implementing additional validation checks in the gsm_cleanup_mux function, and potentially applying runtime protections such as stack canaries or enhanced memory sanitization. The fix should specifically address the dangling pointer issue by ensuring that gsm->dlci is set to NULL immediately after gsm_dlci_release completes. System administrators should prioritize kernel updates to prevent exploitation while monitoring for potential denial-of-service conditions or unexpected behavior in GSM communication systems. This vulnerability demonstrates the importance of careful memory management in kernel drivers and aligns with ATT&CK technique T1068, which covers local privilege escalation through kernel vulnerabilities.