CVE-2025-21756

HIGHPre-NVD 7.87.8—
EchelonGraph scoreMEDIUM confidence

Score 7.8 from GitHub Security Advisory (severity: HIGH) published 2025-02-27. the CNA's CVSS baseline 7.8; sources differ by 0.0.

Triggered by: GitHub Security Advisory CVSS
Sources: cna:linux, epss, ghsa
Elevated
7.8
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 1%CVSS: 7.8Exploit: NoneExposed: 0

A fix is available — apply it.

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:

  • vsock_create() (refcnt=1) calls vsock_insert_unbound() (refcnt=2)
  • transport->release() calls vsock_remove_bound() without checking if
sk was bound and moved to bound list (refcnt=1)
  • 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

CVSS v3
7.8
EG Score
7.8(medium)
EG Risk
51(Track*)
EG Risk 51/100SSVC: Track*

EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).

How it’s computed
Severity78% × 45%
Exploitation40% × 40%
Automatability0% × 15%
Action: Watch closely — could escalate to Attend.
EPSS
54.1%
KEV
Not listed

Published

February 27, 2025

Last Modified

July 14, 2026

Advisory Details (10)

Auto-updated May 12, 2026
⚠️ Active exploitation confirmed. Patch available.
generic🔴 Active Exploitation

SSA-082556

https://cert-portal.siemens.com/productcert/html/ssa-082556.html
generic Patch Available

[SECURITY] [DLA 4193-1] linux-6.1 security update

https://lists.debian.org/debian-lts-announce/2025/05/msg00045.html
generic Patch Available

[SECURITY] [DLA 4178-1] linux security update

https://lists.debian.org/debian-lts-announce/2025/05/msg00030.html
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/fcdd2242c0231032fc84e1404315c245ae56322a
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e7754d564579a5db9c5c9f74228df5d6dd6f1173
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/e48fcb403c2d0e574c19683f09399ab4cf67809c
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/b1afd40321f1c243cffbcf40ea7ca41aca87fa5e
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/645ce25aa0e67895b11d89f27bb86c9d444c40f8
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/42b33381e5e1f2b967dc4fb4221ddb9aaf10d197
generic

vsock: Keep the binding until socket destruction - kernel/git/stable/linux.git - Linux kernel stable tree

https://git.kernel.org/stable/c/3f43540166128951cc1be7ab1ce6b7f05c670d8b

Vendor Advisories for CVE-2025-21756(20)

These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.

Patch Availability(25)

Vendor / EcosystemFixed in / PatchReleasedSource
ubuntulinux-tools-raspi-realtime (6.8.0-2023.24) @ noble2026-05-21ubuntu
ubuntulinux-tools-gkeop-6.8 (6.8.0-1010.12) @ noble2026-05-21ubuntu
ubuntulinux-virtual (6.8.0-58.60) @ noble2026-05-21ubuntu
ubuntulinux-virtual-hwe-24.04-edge (6.11.0-24.24+1) @ oracular2026-05-21ubuntu
ubuntulinux-tools-aws-edge (6.8.0-1027.29~22.04.1) @ jammy2026-05-21ubuntu
ubuntulinux-tools-gcp-edge (6.8.0-1028.30~22.04.1) @ jammy2026-05-21ubuntu
ubuntulinux-tools-realtime-hwe-24.04 (6.8.1-1020.21) @ noble2026-05-21ubuntu
ubuntulinux-virtual-hwe-20.04-edge (5.15.0.138.134) @ jammy2026-05-21ubuntu
ubuntulinux-tools-gcp-fips (5.15.0.1081.71) @ jammy2026-05-21ubuntu
redhatkpatch-patch2025-06-02redhat
redhatkernel-0:5.14.0-427.70.1.el9_42025-05-28redhat
redhatkernel-0:6.12.0-55.13.1.el10_02025-05-26redhat
redhatkernel-0:5.14.0-427.68.2.el9_42025-05-21redhat
redhatkernel-rt-0:4.18.0-553.53.1.rt7.394.el8_102025-05-21redhat
redhatkernel-0:4.18.0-553.53.1.el8_102025-05-21redhat
redhatkernel-0:5.14.0-570.17.1.el9_62025-05-19redhat
redhatkernel-0:4.18.0-305.157.1.el8_42025-05-19redhat
redhatkernel-0:5.14.0-70.132.1.el9_02025-05-19redhat
redhatkernel-rt-0:5.14.0-70.132.1.rt21.204.el9_02025-05-19redhat
redhatkernel-rt-0:4.18.0-305.157.1.rt7.234.el8_42025-05-19redhat
redhatkernel-0:5.14.0-284.117.1.el9_22025-05-15redhat
redhatkernel-0:4.18.0-372.145.1.el8_62025-05-15redhat
redhatkernel-0:4.18.0-477.97.1.el8_82025-05-15redhat
redhatkernel-rt-0:5.14.0-284.117.1.rt14.402.el9_22025-05-15redhat
linuxKernel @ 5.10.235—osv

Patches are aggregated from vendor advisories (Red Hat, Microsoft, Cisco, GitHub) and package ecosystems (OSV, GHSA). Multiple rows for the same upstream release have been deduplicated.

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Additional Vendor Advisories

(5)

Vendors that published advisories for this CVE beyond the curated set above. Broader coverage but minimal per-row detail — click through for the original advisory.

Data Freshness Timeline

(refreshed 11× in last 7d / 47× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 126 total refreshes for this CVE.

  1. 2026-07-23 02:50 UTCEG score recompute
  2. 2026-07-22 14:07 UTCEPSS rescore
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Publicly available exploits

(2 references)

Working exploit code is in the public domain (2 GitHub PoCs). Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • GitHub PoCkhoatran107/cve-2025-21756
    First seen Jun 26, 2025
    Open source ↗
  • GitHub PoChoefler02/CVE-2025-21756
    First seen Apr 18, 2025

    Exploit for CVE-2025-21756 for Linux kernel 6.6.75. My first linux kernel exploit!

    Open source ↗

Frequently asked(5)

What is CVE-2025-21756?
CVE-2025-21756 is a high vulnerability published on February 27, 2025. 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…
When was CVE-2025-21756 disclosed?
CVE-2025-21756 was first published in the National Vulnerability Database on February 27, 2025, with the most recent update on July 14, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2025-21756 actively exploited?
CVE-2025-21756 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 54.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2025-21756?
CVE-2025-21756 has a CVSS v4.0 base score of 7.8 (CNA self-assessment; NVD's own analysis pending).
How do I remediate CVE-2025-21756?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2025-21756, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

Dependency Blast Radius

Explore the affected products and dependency analysis for CVE-2025-21756

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