CVE-2026-68169 mptcp: pm: userspace: fix use-after-free in get_local_id
A use-after-free race condition in the Linux kernel MPTCP userspace path manager allows local attackers to potentially execute code or escalate privileges.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-68169?
CVE-2026-68169 is an use after free vulnerability in Linux, published on 10 Aug 2026. 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:
mptcp: pm: userspace: fix use-after-free in get_local_id
In mptcp_pm_userspace_get_local_id(), the address entry is looked up under spinlock, but its id is read after dropping the lock. A concurrent deletion can free the entry between the unlock and the read, leading to UAF.
The race window is narrow. It was reproduced only with a locally constructed stress test that repeatedly overlaps an MP_JOIN SYN with a MPTCP_PM_CMD_SUBFLOW_DESTROY request.
However, the KASAN report below confirms that the race is reachable:
[ 666.319376] BUG: KASAN: slab-use-after-free in mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319386] Read of size 1 at addr ffff888124845610 by task swapper/0/0 ... [ 666.319401] Call Trace: [ 666.319405] <IRQ> [ 666.319408] dump_stack_lvl+0x53/0x70 [ 666.319412] print_address_description.constprop.0+0x2c/0x3b0 [ 666.319418] print_report+0xbe/0x2b0 [ 666.319421] ? mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319423] kasan_report+0xce/0x100 [ 666.319426] ? mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319429] mptcp_userspace_pm_get_local_id+0x1dc/0x1f0 [ 666.319433] mptcp_pm_get_local_id+0x371/0x440 ... [ 666.319821] Allocated by task 45539: [ 666.319844] kasan_save_stack+0x33/0x60 [ 666.319855] kasan_save_track+0x14/0x30 [ 666.319858] __kasan_kmalloc+0x8f/0xa0 [ 666.319863] __kmalloc_noprof+0x1e7/0x520 [ 666.319867] sock_kmalloc+0xdf/0x130 [ 666.319885] sock_kmemdup+0x1b/0x40 [ 666.319888] mptcp_userspace_pm_append_new_local_addr+0x261/0x500 [ 666.319910] mptcp_pm_nl_announce_doit+0x16a/0x610 ... [ 666.319967] Freed by task 45560: [ 666.319988] kasan_save_stack+0x33/0x60 [ 666.319991] kasan_save_track+0x14/0x30 [ 666.319994] kasan_save_free_info+0x3b/0x60 [ 666.319998] __kasan_slab_free+0x43/0x70 [ 666.320000] kfree+0x166/0x440 [ 666.320003] sock_kfree_s+0x1d/0x50 [ 666.320007] mptcp_userspace_pm_delete_local_addr.isra.0+0x157/0x200 [ 666.320011] mptcp_pm_nl_subflow_destroy_doit+0x51d/0xea0
Fix by copying the id into a local variable while still holding the lock, and use -1 as a "not found" sentinel.
Which versions are affected by CVE-2026-68169?
How do I fix CVE-2026-68169?
Apply the vendor's patch.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
Is CVE-2026-68169 being exploited?
There is no known exploitation of CVE-2026-68169 in the wild and no public exploit code.
Sources
Also known as AZL-94859, BELL-CVE-2026-68169, DEBIAN-CVE-2026-68169, GHSA-479w-3phx-jjxq, UBUNTU-CVE-2026-68169.