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HIGH

CVE-2025-21756

CVSS v3

7.8

HIGH

EPSS Score

0.9 %

exploit probability, as of 2026-10-19

CISA KEV

No

known exploited

Exploitation

—

SSVC status

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Affected and fixed versions

Packages from OSV.dev and products from the vendors' CSAF advisories.

version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.

Packages

  • kernelAlmaLinux:9all versions · fixed in 5.14.0-570.17.1.el9_6and 75 other packages
  • kernelAlmaLinux:8all versions · fixed in 4.18.0-553.53.1.el8_10and 24 other packages
  • kernel-rtAlmaLinux:8all versions · fixed in 4.18.0-553.53.1.rt7.394.el8_10and 9 other packages

Vendor advisories

  • CVE-2025-21756 Red Hat Product Security2,308 products fixed

    kernel: vsock: Keep the binding until socket destruction

  • SSA-784472 Siemens ProductCERT1 known affected

    SSA-784472: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 TM MFP V1.1.1

    SIMATIC S7-1500 TM MFP - GNU/Linux subsystem

  • ICSA-25-162-05 CISA5 known affected

    Siemens SIMATIC S7-1500 CPU family

    SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) · SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0)

  • SSA-082556 Siemens ProductCERT5 known affected

    SSA-082556: Vulnerabilities in the additional GNU/Linux subsystem of the SIMATIC S7-1500 CPU 1518(F)-4 PN/DP MFP V3.1.5

    SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AB0) >= V3.1.5 · SIMATIC S7-1500 CPU 1518-4 PN/DP MFP (6ES7518-4AX00-1AC0) >= V3.1.5 · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFP (6ES7518-4FX00-1AB0) >= V3.1.5

  • RHSA-2025:8347 Red Hat Product Security28 products fixed

    Red Hat Security Advisory: kpatch-patch-4_18_0-372_118_1, kpatch-patch-4_18_0-372_131_1, kpatch-patch-4_18_0-372_137_1, and kpatch-patch-4_18_0-372_91_1 security update

  • RHSA-2025:8348 Red Hat Product Security28 products fixed

    Red Hat Security Advisory: kpatch-patch-4_18_0-305_120_1, kpatch-patch-4_18_0-305_138_1, kpatch-patch-4_18_0-305_145_1, and kpatch-patch-4_18_0-305_150_1 security update

21 more advisories

Full record on NVD

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. WA

Technical details

Published
2025-02-27

Frequently asked questions

What is CVE-2025-21756?

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. WA

Is CVE-2025-21756 actively exploited?

Active exploitation of CVE-2025-21756 has not been confirmed. Its EPSS score was 0.9% on 2026-10-19, the estimated probability of exploitation in the next 30 days.

What is the CVSS score for CVE-2025-21756?

CVE-2025-21756 has a CVSS v3 base score of 7.8 (HIGH severity).

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