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Linux KernelOperating system · Linux

CVE-2025-21812

HIGH · 7.8 CVSS v3.1 Published 2025-02-27
Fix available
A fix is available. Upgrade to 3.19 / 4.5 or later.
See remediation →
80/100
Remediation priority · High
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
In the Linux kernel, the following vulnerability has been resolved: ax25: rcu protect dev->ax25_ptr syzbot found a lockdep issue [1]. We should remove ax25 RTNL dependency in ax25_setsockopt() This should also fix a variety of possible UAF in ax25. [1] WARNING: possible circular locking dependency detected 6.13.0-rc3-syzkaller-00762-g9268abe611b0 #0 Not tainted ------------------------------------------------------ syz.5.1818/12806 is trying to acquire lock: ffffffff8fcb3988 (rtnl_mutex){+.+.}-{4:4}, at: ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680 but task is already holding lock: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1618 [inline] ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x209/0xe90 net/ax25/af_ax25.c:574 which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (sk_lock-AF_AX25){+.+.}-{0:0}: lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 lock_sock_nested+0x48/0x100 net/core/sock.c:3642 lock_sock include/net/sock.h:1618 [inline] ax25_kill_by_device net/ax25/af_ax25.c:101 [inline] ax25_device_event+0x24d/0x580 net/ax25/af_ax25.c:146 notifier_call_chain+0x1a5/0x3f0 kernel/notifier.c:85 __dev_notify_flags+0x207/0x400 dev_change_flags+0xf0/0x1a0 net/core/dev.c:9026 dev_ifsioc+0x7c8/0xe70 net/core/dev_ioctl.c:563 dev_ioctl+0x719/0x1340 net/core/dev_ioctl.c:820 sock_do_ioctl+0x240/0x460 net/socket.c:1234 sock_ioctl+0x626/0x8e0 net/socket.c:1339 vfs_ioctl fs/ioctl.c:51 [inline] __do_sys_ioctl fs/ioctl.c:906 [inline] __se_sys_ioctl+0xf5/0x170 fs/ioctl.c:892 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f -> #0 (rtnl_mutex){+.+.}-{4:4}: check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/locking/lockdep.c:3280 [inline] validate_chain+0x18ef/0x5920 kernel/locking/lockdep.c:3904 __lock_acquire+0x1397/0x2100 kernel/locking/lockdep.c:5226 lock_acquire+0x1ed/0x550 kernel/locking/lockdep.c:5849 __mutex_lock_common kernel/locking/mutex.c:585 [inline] __mutex_lock+0x1ac/0xee0 kernel/locking/mutex.c:735 ax25_setsockopt+0xa55/0xe90 net/ax25/af_ax25.c:680 do_sock_setsockopt+0x3af/0x720 net/socket.c:2324 __sys_setsockopt net/socket.c:2349 [inline] __do_sys_setsockopt net/socket.c:2355 [inline] __se_sys_setsockopt net/socket.c:2352 [inline] __x64_sys_setsockopt+0x1ee/0x280 net/socket.c:2352 do_syscall_x64 arch/x86/entry/common.c:52 [inline] do_syscall_64+0xf3/0x230 arch/x86/entry/common.c:83 entry_SYSCALL_64_after_hwframe+0x77/0x7f other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sk_lock-AF_AX25); lock(rtnl_mutex); lock(sk_lock-AF_AX25); lock(rtnl_mutex); *** DEADLOCK *** 1 lock held by syz.5.1818/12806: #0: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: lock_sock include/net/sock.h:1618 [inline] #0: ffff8880617ac258 (sk_lock-AF_AX25){+.+.}-{0:0}, at: ax25_setsockopt+0x209/0xe90 net/ax25/af_ax25.c:574 stack backtrace: CPU: 1 UID: 0 PID: 12806 Comm: syz.5.1818 Not tainted 6.13.0-rc3-syzkaller-00762-g9268abe611b0 #0 Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 09/13/2024 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x241/0x360 lib/dump_stack.c:120 print_circular_bug+0x13a/0x1b0 kernel/locking/lockdep.c:2074 check_noncircular+0x36a/0x4a0 kernel/locking/lockdep.c:2206 check_prev_add kernel/locking/lockdep.c:3161 [inline] check_prevs_add kernel/lockin ---truncated---

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis
How this class of weakness works · CWE-416

Memory is used after it has been freed, so its contents — now potentially attacker-controlled — drive the program's behaviour. With careful heap grooming this becomes code execution. The fix requires disciplined ownership of memory and often a targeted rework of the object lifecycle.

General guidance for the use after free class — the official description and references above are authoritative for this specific CVE. Want a bespoke review and a reviewed fix? Ask our team →

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 3.18.132, < 3.19>= 4.4.170, < 4.5>= 4.9.149, < 4.10>= 4.14.92, < 4.15>= 4.19.14, < 4.20>= 4.20.1, < 6.1.129>= 6.2, < 6.6.76>= 6.7, < 6.12.13>= 6.13, < 6.13.2

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
High
Availability
High

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.19 / 4.5 / 4.10 or later
Fixed in 3.194.54.10
Vendor patch git.kernel.org →
Recommended fix High confidence

Kernel version 3.19 or later, 4.5 or later, 4.10 or later, or 4.15 or later (depending on which major branch is in use)

  1. 1. Identify the current running kernel version using `uname -r`
  2. 2. Check if the current kernel version falls within the affected range: 3.18.132-3.19, 4.4.170-4.5, 4.9.149-4.10, or 4.14.92-4.15
  3. 3. If affected, upgrade to a kernel version that includes the fix commit 2802ed4ced27ebd474828fc67ffd7d66f11e3605
  4. 4. For Debian systems, apply the Debian kernel security update that addresses this CVE
  5. 5. Reboot the system to load the patched kernel

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $3,200. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-21812 in production — separate from our analysis above.

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