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NVD / CVE Program· CNA Linux

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

Noroxi assessment

Priority: Monitor (action score 31/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 0.89% (FIRST EPSS); higher than 59.6% of all records.
  • Someone with local access to the system can trigger it. A low-privileged account is enough. No user action is required. No special conditions are required; it is repeatable.
  • Fixed version: Linux Linux 3f43540166128951cc1be7ab1ce6b7f05c670d8b, 42b33381e5e1f2b967dc4fb4221ddb9aaf10d197, 645ce25aa0e67895b11d89f27bb86c9d444c40f8; azl3 kernel 6.6.78.1-3 on Azure Linux 3.0 6.6.82.1-1; azl3 kernel 6.6.82.1-1 on Azure Linux 3.0 6.6.82.1-1.

Low priority for now. Upgrade to Linux Linux 3f43540166128951cc1be7ab1ce6b7f05c670d8b, 42b33381e5e1f2b967dc4fb4221ddb9aaf10d197, 645ce25aa0e67895b11d89f27bb86c9d444c40f8; azl3 kernel 6.6.78.1-3 on Azure Linux 3.0 6.6.82.1-1; azl3 kernel 6.6.82.1-1 on Azure Linux 3.0 6.6.82.1-1 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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

HighCVSS 7.8 · v3.1—Proof of concept Fix available
Published
Feb 27, 2025
Updated
Oct 15, 2026
EPSS
0.8% · 59th percentile

Report tools

JSON

Action score

31

Monitor

Low priority for now.

CVSS
31 / 40 · 7.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.8%

CISA SSVC decision

Exploitation
proof of concept
Automatable
no
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · Linux
7.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

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  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
linuxlinux kernel

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • linux linux kernel5.5 and later · before 5.10.235
  • linux linux kernel5.11 and later · before 5.15.179
  • linux linux kernel5.16 and later · before 6.1.131
  • linux linux kernel6.2 and later · before 6.6.79
  • linux linux kernel6.7 and later · before 6.12.16
  • linux linux kernel6.13 and later · before 6.13.4

Versions reported by the vendor

Affected version ranges reported by the assigning authority (Linux). Independent of NVD's CPE analysis and usually ahead of it.

  • Linux Linux

    • 5.5affected
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before e7754d564579a5db9c5c9f74228df5d6dd6f1173affected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before e48fcb403c2d0e574c19683f09399ab4cf67809caffected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before 42b33381e5e1f2b967dc4fb4221ddb9aaf10d197affected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before 3f43540166128951cc1be7ab1ce6b7f05c670d8baffected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before 645ce25aa0e67895b11d89f27bb86c9d444c40f8affected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before b1afd40321f1c243cffbcf40ea7ca41aca87fa5eaffected · git
    • c0cfa2d8a788fcf45df5bf4070ab2474c88d543a and later · before fcdd2242c0231032fc84e1404315c245ae56322aaffected · git
    • before 5.5not affected · semver
    • 5.10.235 and later · up to and including 5.10.*not affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
AlmaLinux:8bpftoolbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernelbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-abi-stablelistsbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-corebefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-cross-headersbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-debugbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-debug-corebefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-debug-develbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-debug-modulesbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-debug-modules-extrabefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-develbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-docbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-headersbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-modulesbefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-modules-extrabefore 4.18.0-553.53.1.el8_104.18.0-553.53.1.el8_10
AlmaLinux:8kernel-rtbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-corebefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-debugbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-debug-corebefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-debug-develbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-debug-modulesbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-debug-modules-extrabefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-develbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10
AlmaLinux:8kernel-rt-modulesbefore 4.18.0-553.53.1.rt7.394.el8_104.18.0-553.53.1.rt7.394.el8_10

+96

Same product

linux: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-31431crypto: algif_aead - Revert to operating out-of-placeKEV
    90Now
  • CVE-2022-0847A flaw was found in the way the "flags" member of the new pipe buffer structure was lacking proper initialization in copy_page_to_iter_pipe KEV
    89Now
  • CVE-2021-22555Heap Out-Of-Bounds Write in Netfilter IP6T_SO_SET_REPLACEKEV
    85Now

Published before and after this one in the same product

  • ← EarlierCVE-2025-21750Feb 27, 2025 · wifi: brcmfmac: Check the return value of of_property_read_string_index()
    22Monitor
  • ← EarlierCVE-2025-21753Feb 27, 2025 · btrfs: fix use-after-free when attempting to join an aborted transaction
    31Monitor
  • Later →CVE-2025-21758Feb 27, 2025 · ipv6: mcast: add RCU protection to mld_newpack()
    27Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
Linux Linux3f43540166128951cc1be7ab1ce6b7f05c670d8bVendor (CNA)
Linux Linux42b33381e5e1f2b967dc4fb4221ddb9aaf10d197Vendor (CNA)
Linux Linux645ce25aa0e67895b11d89f27bb86c9d444c40f8Vendor (CNA)
Linux Linuxb1afd40321f1c243cffbcf40ea7ca41aca87fa5eVendor (CNA)
Linux Linuxe48fcb403c2d0e574c19683f09399ab4cf67809cVendor (CNA)
Linux Linuxe7754d564579a5db9c5c9f74228df5d6dd6f1173Vendor (CNA)
Linux Linuxfcdd2242c0231032fc84e1404315c245ae56322aVendor (CNA)
azl3 kernel 6.6.78.1-3 on Azure Linux 3.06.6.82.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
azl3 kernel 6.6.82.1-1 on Azure Linux 3.06.6.82.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.176.3-3 on CBL Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.176.3-3 on CBL-Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
cbl2 kernel 5.15.180.1-1 on CBL Mariner 2.05.15.180.1-1 · CBL-Mariner ReleasesMicrosoft (MSRC)
almalinux:kernel5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-core5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-core5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-devel5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-devel-matched5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-modules5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-modules-core5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-debug-modules-extra5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-devel5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
almalinux:kernel-64k-devel-matched5.14.0-570.17.1.el9_6 · AlmaLinux:9Package registry (OSV)
debian:linux6.1.133-1 · Debian:12Package registry (OSV)
red hat:bpftool0:4.18.0-372.145.1.el8_6 · Red Hat:rhel_aus:8.6::baseosPackage registry (OSV)
red hat:bpftool-debuginfo0:4.18.0-372.145.1.el8_6 · Red Hat:rhel_aus:8.6::baseosPackage registry (OSV)
red hat:kernel0:4.18.0-372.145.1.el8_6 · Red Hat:rhel_aus:8.6::baseosPackage registry (OSV)
red hat:kernel-abi-stablelists0:4.18.0-372.145.1.el8_6 · Red Hat:rhel_aus:8.6::baseosPackage registry (OSV)
red hat:kernel-core0:4.18.0-372.145.1.el8_6 · Red Hat:rhel_aus:8.6::baseosPackage registry (OSV)

+21

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×4

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:1582025-04-18
Proof-of-concept repository on GitHubstars:02025-06-19
Proof-of-concept repository on GitHubstars:92025-06-26
Proof-of-concept repository on GitHubstars:12026-03-22

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+50 d
  3. TodayNov 8, 2026+620 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Someone with local access to the system can trigger it.
  • A low-privileged account is enough.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Local
Attack complexity
Low
Privileges required
Low
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-416 · Use After Free

CVSS vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Root cause

After a memory region is freed, another reference pointing to it is still used. By then, the same region may have been allocated for different data.

The bug in code

The whole CWE-416 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

c
free(dev->buf);/* ... another thread is still running ... */process(dev->buf);

Fixed

c
lock(&dev->lock);free(dev->buf);dev->buf = NULL;unlock(&dev->lock);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

MITRE has no CAPEC/ATT&CK mapping for this CWE.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (11 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records