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Medium severity5.5NVD Advisory· Published Mar 12, 2025· Updated May 12, 2026

CVE-2025-21862

CVE-2025-21862

Description

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

drop_monitor: fix incorrect initialization order

Syzkaller reports the following bug:

BUG: spinlock bad magic on CPU#1, syz-executor.0/7995 lock: 0xffff88805303f3e0, .magic: 00000000, .owner: /-1, .owner_cpu: 0 CPU: 1 PID: 7995 Comm: syz-executor.0 Tainted: G E 5.10.209+ #1 Hardware name: VMware, Inc. VMware Virtual Platform/440BX Desktop Reference Platform, BIOS 6.00 11/12/2020 Call Trace: __dump_stack lib/dump_stack.c:77 [inline] dump_stack+0x119/0x179 lib/dump_stack.c:118 debug_spin_lock_before kernel/locking/spinlock_debug.c:83 [inline] do_raw_spin_lock+0x1f6/0x270 kernel/locking/spinlock_debug.c:112 __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:117 [inline] _raw_spin_lock_irqsave+0x50/0x70 kernel/locking/spinlock.c:159 reset_per_cpu_data+0xe6/0x240 [drop_monitor] net_dm_cmd_trace+0x43d/0x17a0 [drop_monitor] genl_family_rcv_msg_doit+0x22f/0x330 net/netlink/genetlink.c:739 genl_family_rcv_msg net/netlink/genetlink.c:783 [inline] genl_rcv_msg+0x341/0x5a0 net/netlink/genetlink.c:800 netlink_rcv_skb+0x14d/0x440 net/netlink/af_netlink.c:2497 genl_rcv+0x29/0x40 net/netlink/genetlink.c:811 netlink_unicast_kernel net/netlink/af_netlink.c:1322 [inline] netlink_unicast+0x54b/0x800 net/netlink/af_netlink.c:1348 netlink_sendmsg+0x914/0xe00 net/netlink/af_netlink.c:1916 sock_sendmsg_nosec net/socket.c:651 [inline] __sock_sendmsg+0x157/0x190 net/socket.c:663 ____sys_sendmsg+0x712/0x870 net/socket.c:2378 ___sys_sendmsg+0xf8/0x170 net/socket.c:2432 __sys_sendmsg+0xea/0x1b0 net/socket.c:2461 do_syscall_64+0x30/0x40 arch/x86/entry/common.c:46 entry_SYSCALL_64_after_hwframe+0x62/0xc7 RIP: 0033:0x7f3f9815aee9 Code: ff ff c3 66 2e 0f 1f 84 00 00 00 00 00 0f 1f 40 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 b0 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007f3f972bf0c8 EFLAGS: 00000246 ORIG_RAX: 000000000000002e RAX: ffffffffffffffda RBX: 00007f3f9826d050 RCX: 00007f3f9815aee9 RDX: 0000000020000000 RSI: 0000000020001300 RDI: 0000000000000007 RBP: 00007f3f981b63bd R08: 0000000000000000 R09: 0000000000000000 R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000 R13: 000000000000006e R14: 00007f3f9826d050 R15: 00007ffe01ee6768

If drop_monitor is built as a kernel module, syzkaller may have time to send a netlink NET_DM_CMD_START message during the module loading. This will call the net_dm_monitor_start() function that uses a spinlock that has not yet been initialized.

To fix this, let's place resource initialization above the registration of a generic netlink family.

Found by InfoTeCS on behalf of Linux Verification Center (linuxtesting.org) with Syzkaller.

AI Insight

LLM-synthesized narrative grounded in this CVE's description and references.

The Linux kernel's drop_monitor has an incorrect initialization order causing a spinlock bug, allowing local denial of service via unprivileged netlink messages.

Vulnerability

Description

The Linux kernel's drop_monitor module suffers from an incorrect initialization order vulnerability. A spinlock used within the reset_per_cpu_data function is accessed before proper initialization, leading to a 'spinlock bad magic' BUG. This issue is triggered when a user sends a netlink command via net_dm_cmd_trace, which calls reset_per_cpu_data and attempts to lock an uninitialized spinlock, causing a kernel crash [1][2].

Attack

Vector

An unprivileged local attacker can exploit this by sending a crafted netlink message to the drop_monitor generic netlink family. The attacker does not require any special capabilities beyond the ability to create a netlink socket. The kernel panics with a spinlock debug assertion, leading to a denial of service condition on the affected system.

Impact

Successful exploitation results in a local denial of service due to a kernel BUG, crashing the system. This can be leveraged to disrupt services or as part of a larger attack chain. The vulnerability is rated with a CVSS v3 base score of 5.5 (Medium) and has been confirmed to affect various Siemens industrial products, including the SIMATIC S7-1500 CPU family and the TM MFP GNU/Linux subsystem, across all versions [1][2].

Mitigation

The issue is fixed in later Linux kernel versions. The fix is committed in the stable kernel trees (commits 0efa6c42f81c and b7859e8643e9), but the referenced kernel.org pages are behind a proof-of-work challenge [3][4]. Administrators should apply the latest kernel updates from their distribution or vendor. For affected Siemens devices, refer to the security advisories SSA-265688 and SSA-082556 for specific remediation guidance [1][2].

References
  1. SSA-265688
  2. SSA-082556
  3. Making sure you're not a bot!
  4. Making sure you're not a bot!

AI Insight generated on May 20, 2026. Synthesized from this CVE's description and the cited reference URLs; citations are validated against the source bundle.

Affected products

89

Patches

0

No patches discovered yet.

Vulnerability mechanics

AI mechanics synthesis has not run for this CVE yet.

References

12

News mentions

0

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