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CVE Record

CVE-2025-39860: Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen()

In the Linux kernel, the following vulnerability has been resolved: Bluetooth: Fix use-after-free in l2cap_sock_cleanup_listen() syzbot reported the splat below without a repro. In the splat, a single thread calling bt_accept_dequeue() freed sk and touched it after that. The root cause would be the racy l2cap_sock_cleanup_listen() call added by the cited commit. bt_accept_dequeue() is called under lock_sock() except for l2cap_sock_release(). Two threads could see the same socket during the list iteration in bt_accept_dequeue(): CPU1 CPU2 (close()) ---- ---- sock_hold(sk) sock_hold(sk); lock_sock(sk) <-- block close() sock_put(sk) bt_accept_unlink(sk) sock_put(sk) <-- refcnt by bt_accept_enqueue() release_sock(sk) lock_sock(sk) sock_put(sk) bt_accept_unlink(sk) sock_put(sk) <-- last refcnt bt_accept_unlink(sk) <-- UAF Depending on the timing, the other thread could show up in the "Freed by task" part. Let's call l2cap_sock_cleanup_listen() under lock_sock() in l2cap_sock_release(). [0]: BUG: KASAN: slab-use-after-free in debug_spin_lock_before kernel/locking/spinlock_debug.c:86 [inline] BUG: KASAN: slab-use-after-free in do_raw_spin_lock+0x26f/0x2b0 kernel/locking/spinlock_debug.c:115 Read of size 4 at addr ffff88803b7eb1c4 by task syz.5.3276/16995 CPU: 3 UID: 0 PID: 16995 Comm: syz.5.3276 Not tainted syzkaller #0 PREEMPT(full) Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.16.3-debian-1.16.3-2~bpo12+1 04/01/2014 Call Trace: <TASK> __dump_stack lib/dump_stack.c:94 [inline] dump_stack_lvl+0x116/0x1f0 lib/dump_stack.c:120 print_address_description mm/kasan/report.c:378 [inline] print_report+0xcd/0x630 mm/kasan/report.c:482 kasan_report+0xe0/0x110 mm/kasan/report.c:595 debug_spin_lock_before kernel/locking/spinlock_debug.c:86 [inline] do_raw_spin_lock+0x26f/0x2b0 kernel/locking/spinlock_debug.c:115 spin_lock_bh include/linux/spinlock.h:356 [inline] release_sock+0x21/0x220 net/core/sock.c:3746 bt_accept_dequeue+0x505/0x600 net/bluetooth/af_bluetooth.c:312 l2cap_sock_cleanup_listen+0x5c/0x2a0 net/bluetooth/l2cap_sock.c:1451 l2cap_sock_release+0x5c/0x210 net/bluetooth/l2cap_sock.c:1425 __sock_release+0xb3/0x270 net/socket.c:649 sock_close+0x1c/0x30 net/socket.c:1439 __fput+0x3ff/0xb70 fs/file_table.c:468 task_work_run+0x14d/0x240 kernel/task_work.c:227 resume_user_mode_work include/linux/resume_user_mode.h:50 [inline] exit_to_user_mode_loop+0xeb/0x110 kernel/entry/common.c:43 exit_to_user_mode_prepare include/linux/irq-entry-common.h:225 [inline] syscall_exit_to_user_mode_work include/linux/entry-common.h:175 [inline] syscall_exit_to_user_mode include/linux/entry-common.h:210 [inline] do_syscall_64+0x3f6/0x4c0 arch/x86/entry/syscall_64.c:100 entry_SYSCALL_64_after_hwframe+0x77/0x7f RIP: 0033:0x7f2accf8ebe9 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 a8 ff ff ff f7 d8 64 89 01 48 RSP: 002b:00007ffdb6cb1378 EFLAGS: 00000246 ORIG_RAX: 00000000000001b4 RAX: 0000000000000000 RBX: 00000000000426fb RCX: 00007f2accf8ebe9 RDX: 0000000000000000 RSI: 000000000000001e RDI: 0000000000000003 RBP: 00007f2acd1b7da0 R08: 0000000000000001 R09: 00000012b6cb166f R10: 0000001b30e20000 R11: 0000000000000246 R12: 00007f2acd1b609c R13: 00007f2acd1b6090 R14: ffffffffffffffff R15: 00007ffdb6cb1490 </TASK> Allocated by task 5326: kasan_save_stack+0x33/0x60 mm/kasan/common.c:47 kasan_save_track+0x14/0x30 mm/kasan/common.c:68 poison_kmalloc_redzone mm/kasan/common.c:388 [inline] __kasan_kmalloc+0xaa/0xb0 mm/kasan/common.c:405 kasan_kmalloc include/linux/kasan.h:260 [inline] __do_kmalloc_node mm/slub.c:4365 [inline] __kmalloc_nopro ---truncated---

UnknownCVSS not scoredNot KEV-listedUpdated
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Glexia's TakeAutomated analysisunknown

Security readout for executives and security teams

Plain-English summary

CVE-2025-39860 is a Linux kernel Bluetooth flaw. A race condition can cause the kernel to use memory after it has been freed during L2CAP socket cleanup. The public record shows a syzbot crash report and kernel fixes, but no CVSS score or confirmed exploitation.

Executive priority

Treat this as a tracked kernel maintenance issue, not an emergency based on current evidence. Patch affected systems through normal kernel update channels, accelerating where Bluetooth is enabled on exposed or high-value assets.

Technical view

The issue is a use-after-free in l2cap_sock_cleanup_listen() involving bt_accept_dequeue() during concurrent Bluetooth socket release paths. The fix moves l2cap_sock_cleanup_listen() under lock_sock() in l2cap_sock_release() to prevent two threads from handling the same socket unsafely.

Likely exposure

Exposure is limited to systems running affected Linux kernel versions with the Bluetooth L2CAP code present. The source bundle lists multiple affected stable kernel lines and Debian LTS references. It does not identify specific application packages, cloud services, or remote attack prerequisites.

Exploitation context

The public source states syzbot reported the crash without a reproducer. KEV status is false, and the bundle provides no evidence of active exploitation, public exploit code, or weaponized use. Attacker prerequisites and practical impact are not fully documented in the provided sources.

Researcher notes

The source record indicates a race in Bluetooth socket cleanup found by syzbot/KASAN, with no reproducer. Practical exploitability, privilege requirements, and impact beyond kernel memory safety are not established in the provided bundle.

Mitigation direction

  • Prioritize kernel updates from your Linux distribution or device vendor.
  • Track the referenced stable kernel commits for fixed kernel availability.
  • Review Debian LTS notices if operating affected Debian systems.
  • Check Siemens advisories if managing referenced Siemens products.
  • If patching is delayed, review vendor guidance for Bluetooth exposure reduction.

Validation and detection

  • Inventory Linux kernel versions across servers, endpoints, appliances, and embedded systems.
  • Compare running kernels against the affected and fixed versions in the CVE record.
  • Confirm whether Bluetooth and L2CAP functionality are enabled where not required.
  • Verify vendor advisories for backported fixes, not just upstream version numbers.
  • Check vulnerability scanners for CVE-2025-39860 coverage and false negatives.
Prepared
Confidence
medium
Sources
12

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

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CVE-2025-39860 mapping review

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Vulnerability profileCVE Program record
Severity
Unknown
CVSS
Not scored
Known Exploited
No
Published
Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

0CVSS vectors
3Timeline events
2ADP providers
13Source links

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. CVE publishedCVE Program

    The CVE record was published.

  3. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CVECVE Program Container
siemens-SADPADP container

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
LinuxLinuxa2da00d1ea1abfb04f846638e210b5b5166e3c9c, 06f87c96216bc5cd1094c23492274f77f1d5dd3b, fbe5a2fed8156cc19eb3b956602b0a1dd46a302d, 29fac18499332211b2615ade356e2bd8b3269f98, 1728137b33c00d5a2b5110ed7aafb42e7c32e4a1, 1728137b33c00d5a2b5110ed7aafb42e7c32e4a1, 1728137b33c00d5a2b5110ed7aafb42e7c32e4a1, 1728137b33c00d5a2b5110ed7aafb42e7c32e4a1, 51822644a047eac2310fab0799b64e3430b5a111, 82cdb2ccbe43337798393369f0ceb98699fe6037, 10426afe65c8bf7b24dd0c7be4dcc65f86fc99f9, 5.4.253, 5.10.190, 5.15.126, 6.1.45, 4.14.322, 4.19.291, 6.4.10unaffected
LinuxLinux6.5, 0, 5.4.299, 5.10.243, 5.15.192, 6.1.151, 6.6.105, 6.12.46, 6.16.6, 6.17affected
Weakness

CWE details

No CWE listed

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