EUVD-2026-59404
GHSA-9q9r-2g23-7q72
Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local access with low privileges suffices to trigger the race; once sockmap is configured AC:L is appropriate given syzbot's reliable reproduction; full C/I/A from kernel heap UAF.
Primary rating from Vendor (Linux).
CVSS VectorVendor: Linux
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Lifecycle Timeline
5DescriptionCVE.org
In the Linux kernel, the following vulnerability has been resolved:
sockmap: Fix use-after-free in udp_bpf_recvmsg()
syzbot reported use-after-free of struct sk_msg in sk_msg_recvmsg(). [0]
sk_msg_recvmsg() peeks sk_msg from psock->ingress_msg under a lock, but its processing is lockless.
Thus, sk_msg_recvmsg() must be serialised by callers, otherwise multiple threads could touch the same sk_msg.
For example, TCP uses lock_sock(), and AF_UNIX uses unix_sk(sk)->iolock.
Initially, udp_bpf_recvmsg() had used lock_sock(), but the cited commit removed it.
Let's serialise sk_msg_recvmsg() with lock_sock() in udp_bpf_recvmsg().
Note that holding spin_lock_bh(&sk->sk_receive_queue.lock) is not an option due to copy_page_to_iter() in sk_msg_recvmsg().
[0]: BUG: KASAN: slab-use-after-free in sk_msg_recvmsg+0xb54/0xc30 net/core/skmsg.c:428 Read of size 4 at addr ffff88814cdcf000 by task syz.0.24/6020
CPU: 1 UID: 0 PID: 6020 Comm: syz.0.24 Not tainted syzkaller #0 PREEMPT(full) Hardware name: Google Compute Engine/Google Compute Engine, BIOS Google 01/13/2026 Call Trace: <TASK> dump_stack_lvl+0xe8/0x150 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xba/0x230 mm/kasan/report.c:482 kasan_report+0x117/0x150 mm/kasan/report.c:595 sk_msg_recvmsg+0xb54/0xc30 net/core/skmsg.c:428 udp_bpf_recvmsg+0x4bd/0xe00 net/ipv4/udp_bpf.c:84 inet_recvmsg+0x260/0x270 net/ipv4/af_inet.c:891 sock_recvmsg_nosec net/socket.c:1078 [inline] sock_recvmsg+0x1a8/0x270 net/socket.c:1100 ____sys_recvmsg+0x1e6/0x4a0 net/socket.c:2812 ___sys_recvmsg+0x215/0x590 net/socket.c:2854 do_recvmmsg+0x334/0x800 net/socket.c:2949 __sys_recvmmsg net/socket.c:3023 [inline] __do_sys_recvmmsg net/socket.c:3046 [inline] __se_sys_recvmmsg net/socket.c:3039 [inline] __x64_sys_recvmmsg+0x198/0x250 net/socket.c:3039 do_syscall_x64 arch/x86/entry/syscall_64.c:63 [inline] do_syscall_64+0xe2/0xf80 arch/x86/entry/syscall_64.c:94 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7fb319f9aeb9 Code: ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 44 00 00 48 89 f8 48 89 f7 48 89 d6 48 89 ca 4d 89 c2 4d 89 c8 4c 8b 4c 24 08 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007fb31ad97028 EFLAGS: 00000246 ORIG_RAX: 000000000000012b RAX: ffffffffffffffda RBX: 00007fb31a216090 RCX: 00007fb319f9aeb9 RDX: 0000000000000001 RSI: 0000200000000400 RDI: 0000000000000004 RBP: 00007fb31a008c1f R08: 0000000000000000 R09: 0000000000000000 R10: 0000000040000021 R11: 0000000000000246 R12: 0000000000000000 R13: 00007fb31a216128 R14: 00007fb31a216090 R15: 00007ffe21dd0a98 </TASK>
Allocated by task 6019: kasan_save_stack mm/kasan/common.c:57 [inline] kasan_save_track+0x3e/0x80 mm/kasan/common.c:78 poison_kmalloc_redzone mm/kasan/common.c:398 [inline] __kasan_kmalloc+0x93/0xb0 mm/kasan/common.c:415 kasan_kmalloc include/linux/kasan.h:263 [inline] __kmalloc_cache_noprof+0x3d1/0x6e0 mm/slub.c:5780 kmalloc_noprof include/linux/slab.h:957 [inline] kzalloc_noprof include/linux/slab.h:1094 [inline] alloc_sk_msg net/core/skmsg.c:510 [inline] sk_psock_skb_ingress_self+0x60/0x350 net/core/skmsg.c:612 sk_psock_verdict_apply net/core/skmsg.c:1038 [inline] sk_psock_verdict_recv+0x7d9/0x8d0 net/core/skmsg.c:1236 udp_read_skb+0x73e/0x7e0 net/ipv4/udp.c:2045 sk_psock_verdict_data_ready+0x12d/0x550 net/core/skmsg.c:1257 __udp_enqueue_schedule_skb+0xc54/0x10b0 net/ipv4/udp.c:1789 __udp_queue_rcv_skb net/ipv4/udp.c:2346 [inline] udp_queue_rcv_one_skb+0xac5/0x19c0 net/ipv4/udp.c:2475 __udp4_lib_mcast_deliver+0xc06/0xcf0 net/ipv4/udp.c:2585 __udp4_lib_rcv+0x10f6/0x2620 net/ipv4/udp.c:2724 ip_protocol_deliver_rcu+0x282/0x440 net/ipv4/ip_input.c:207 ip_local_deliver_finish+0x3bb/0x6f0 net/ipv4/ip_input.c:241 NF_HOOK+0x336/0x3c0 include/linux/netfilter.h:318 dst_input include/net/dst.h:474 [inline] ip_sublist_rcv_finish+0x221/0x2a0 net/ipv4/ip_input.c:584 ip_list_rcv_finish net/ipv4/ip_inp ---truncated---
AnalysisAI
Use-after-free in the Linux kernel's BPF sockmap UDP receive path allows a local low-privileged attacker to corrupt kernel heap memory, enabling potential privilege escalation, kernel memory disclosure, or system crash. The race condition in udp_bpf_recvmsg() allows concurrent threads to access a sk_msg structure after it has been freed, because a prior refactor removed the lock_sock() serialization that TCP and AF_UNIX sockets retain. …
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Vulnerability AssessmentAI
| Exploitation | Exploitation requires all of the following: (1) local system access with at minimum low-privilege credentials, consistent with CVSS PR:L; (2) a UDP socket with an active BPF sockmap program attached via psock - this setup is non-default and typically requires CAP_NET_ADMIN or CAP_BPF privileges to configure, meaning a privileged process must have already established the sockmap context; (3) the ability to spawn multiple concurrent threads calling recvmsg() on that socket to win the race between sk_msg peek and free. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | CVSS 7.8 (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) correctly characterizes this as a high-severity local vulnerability, but real-world exploitability is significantly constrained by several factors. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | A local attacker on a Linux host where a privileged service has attached a BPF sockmap program to a UDP socket spawns multiple threads simultaneously issuing recvmsg() system calls on that socket. Two threads concurrently peek the same sk_msg from the psock ingress queue; thread A processes and frees the structure while thread B continues reading fields within the freed slab object at net/core/skmsg.c:428. … |
| Remediation | Upgrade to a patched kernel version: Linux 6.18.40, 7.1.5, or 7.2-rc1 per EUVD-confirmed fix data. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, conduct an asset inventory of all Linux systems in production and determine which enable BPF functionality, prioritizing servers hosting critical applications or multi-tenant workloads. …
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