CVE-2025-38666

In the Linux kernel, the following vulnerability has been resolved:

net: appletalk: Fix use-after-free in AARP proxy probe

The AARP proxy‐probe routine (aarp_proxy_probe_network) sends a probe, releases the aarp_lock, sleeps, then re-acquires the lock. During that window an expire timer thread (__aarp_expire_timer) can remove and kfree() the same entry, leading to a use-after-free.

race condition:

     cpu 0                          |            cpu 1
atalk_sendmsg()                     |   atif_proxy_probe_device()
aarp_send_ddp()                     |   aarp_proxy_probe_network()
mod_timer()                         |   lock(aarp_lock) // LOCK!!
timeout around 200ms                |   alloc(aarp_entry)
and then call                       |   proxies[hash] = aarp_entry
aarp_expire_timeout()               |   aarp_send_probe()
                                    |   unlock(aarp_lock) // UNLOCK!!
lock(aarp_lock) // LOCK!!           |   msleep(100);
__aarp_expire_timer(&proxies[ct])   |
free(aarp_entry)                    |
unlock(aarp_lock) // UNLOCK!!       |
                                    |   lock(aarp_lock) // LOCK!!
                                    |   UAF aarp_entry !!

================================================================== BUG: KASAN: slab-use-after-free in aarp_proxy_probe_network+0x560/0x630 net/appletalk/aarp.c:493 Read of size 4 at addr ffff8880123aa360 by task repro/13278

CPU: 3 UID: 0 PID: 13278 Comm: repro Not tainted 6.15.2 #3 PREEMPT(full) Call Trace: __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1b0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:408 [inline] print_report+0xc1/0x630 mm/kasan/report.c:521 kasan_report+0xca/0x100 mm/kasan/report.c:634 aarp_proxy_probe_network+0x560/0x630 net/appletalk/aarp.c:493 atif_proxy_probe_device net/appletalk/ddp.c:332 [inline] atif_ioctl+0xb58/0x16c0 net/appletalk/ddp.c:857 atalk_ioctl+0x198/0x2f0 net/appletalk/ddp.c:1818 sock_do_ioctl+0xdc/0x260 net/socket.c:1190 sock_ioctl+0x239/0x6a0 net/socket.c:1311 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl fs/ioctl.c:892 [inline] __x64_sys_ioctl+0x194/0x200 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xcb/0x250 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f

Allocated: aarp_alloc net/appletalk/aarp.c:382 [inline] aarp_proxy_probe_network+0xd8/0x630 net/appletalk/aarp.c:468 atif_proxy_probe_device net/appletalk/ddp.c:332 [inline] atif_ioctl+0xb58/0x16c0 net/appletalk/ddp.c:857 atalk_ioctl+0x198/0x2f0 net/appletalk/ddp.c:1818

Freed: kfree+0x148/0x4d0 mm/slub.c:4841 __aarp_expire net/appletalk/aarp.c:90 [inline] __aarp_expire_timer net/appletalk/aarp.c:261 [inline] aarp_expire_timeout+0x480/0x6e0 net/appletalk/aarp.c:317

The buggy address belongs to the object at ffff8880123aa300 which belongs to the cache kmalloc-192 of size 192 The buggy address is located 96 bytes inside of freed 192-byte region [ffff8880123aa300, ffff8880123aa3c0)

Memory state around the buggy address: ffff8880123aa200: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ffff8880123aa280: 00 00 00 00 fc fc fc fc fc fc fc fc fc fc fc fc

ffff8880123aa300: fa fb fb fb fb fb fb fb fb fb fb fb fb fb fb fb ^ ffff8880123aa380: fb fb fb fb fb fb fb fb fc fc fc fc fc fc fc fc ffff8880123aa400: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ==================================================================

Weakness

The product reuses or references memory after it has been freed. At some point afterward, the memory may be allocated again and saved in another pointer, while the original pointer references a location somewhere within the new allocation. Any operations using the original pointer are no longer valid because the memory “belongs” to the code that operates on the new pointer.

Affected Software

Potential Mitigations

References

• https://git.kernel.org/stable/c/186942d19c0222617ef61f50e1dba91e269a5963
• https://git.kernel.org/stable/c/2a6209e4649d45fd85d4193abc481911858ffc6f
• https://git.kernel.org/stable/c/5f02ea0f63dd38c41539ea290fcc1693c73aa8e5
• https://git.kernel.org/stable/c/6c4a92d07b0850342d3becf2e608f805e972467c
• https://git.kernel.org/stable/c/82d19a70ced28b17a38ebf1b6978c6c7db894979
• https://git.kernel.org/stable/c/b35694ffabb2af308a1f725d70f60fd8a47d1f3e
• https://git.kernel.org/stable/c/e4f1564c5b699eb89b3040688fd6b4e57922f1f6
• https://git.kernel.org/stable/c/f90b6bb203f3f38bf2b3d976113d51571df9a482
• https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html
• https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html