CVE-2025-21756
Linux Kernel Vsock Use-After-Free Vulnerability
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
INFO
Published Date :
Feb. 27, 2025, 3:15 a.m.
Last Modified :
April 30, 2025, 2:15 p.m.
Source :
416baaa9-dc9f-4396-8d5f-8c081fb06d67
Remotely Exploitable :
No
Impact Score :
5.9
Exploitability Score :
1.8
Public PoC/Exploit Available at Github
CVE-2025-21756 has a 6 public PoC/Exploit available at Github.
Go to the Public Exploits tab to see the list.
References to Advisories, Solutions, and Tools
Here, you will find a curated list of external links that provide in-depth
information, practical solutions, and valuable tools related to
CVE-2025-21756.
We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).
None
C
Exploit for CVE-2025-21756 for Linux kernel 6.6.75. My first linux kernel exploit!
Shell C
Latest CVEs with their Proof of Concept exploits.
Python
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Results are limited to the first 15 repositories due to potential performance issues.
The following list is the news that have been mention
CVE-2025-21756 vulnerability anywhere in the article.
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Daily CyberSecurity
Critical UAF Vulnerability Discovered in Ladybird Browser Engine (CVE-2025-47154)
The Ladybird browser engine, a relatively new entrant originating from the SerenityOS project, has been found to contain a critical security vulnerability. Security researcher Jess has identified a us ... Read more
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Cyber Security News
Critical Linux Kernel Vulnerability Exposes Systems to Privilege Escalation Attacks
A significant vulnerability in the Linux kernel’s Virtual Socket (vsock) implementation, designated as CVE-2025-21756, has been identified that could allow local attackers to escalate privileges to ro ... Read more
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Daily CyberSecurity
Apache Tomcat Security Update Fixes DoS and Rewrite Rule Bypass Flaws
The Apache Software Foundation has released important security updates to address two vulnerabilities affecting multiple versions of Apache Tomcat, the widely used open-source Java Servlet container. ... Read more
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Daily CyberSecurity
CVE-2025-21756: How a Tiny Linux Kernel Bug Led to a Full Root Exploit, PoC Releases
In a recently analysis, security researcher Michael Hoefler has exposed the full depth of CVE-2025-21756, a Use-After-Free (UAF) vulnerability affecting the Linux kernel’s vsock subsystem. What began ... Read more
The following table lists the changes that have been made to the
CVE-2025-21756 vulnerability over time.
Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.
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CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Apr. 30, 2025
Action Type Old Value New Value Added Reference https://github.com/hoefler02/CVE-2025-21756/blob/main/x.c -
Initial Analysis by [email protected]
Mar. 24, 2025
Action Type Old Value New Value Added CPE Configuration OR *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.13 up to (excluding) 6.13.4 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.2 up to (excluding) 6.6.79 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 6.7 up to (excluding) 6.12.16 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.11 up to (excluding) 5.15.179 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.5 up to (excluding) 5.10.235 *cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:* versions from (including) 5.16 up to (excluding) 6.1.131 Added Reference Type kernel.org: https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197 Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8 Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173 Types: Patch Added Reference Type kernel.org: https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a Types: Patch -
CVE Modified by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Mar. 13, 2025
Action Type Old Value New Value Added Reference https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197 Added Reference https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c Added Reference https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173 -
CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0
Feb. 27, 2025
Action Type Old Value New Value Added CVSS V3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H Added CWE CWE-416 -
New CVE Received by 416baaa9-dc9f-4396-8d5f-8c081fb06d67
Feb. 27, 2025
Action Type Old Value New Value Added 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 Added Reference https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b Added Reference https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8 Added Reference https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e Added Reference https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a
CWE - Common Weakness Enumeration
While CVE identifies
specific instances of vulnerabilities, CWE categorizes the common flaws or
weaknesses that can lead to vulnerabilities. CVE-2025-21756 is
associated with the following CWEs:
Common Attack Pattern Enumeration and Classification (CAPEC)
Common Attack Pattern Enumeration and Classification
(CAPEC)
stores attack patterns, which are descriptions of the common attributes and
approaches employed by adversaries to exploit the CVE-2025-21756
weaknesses.