CVE-2025-21796Network attack vector

Kernel memory disclosure and crash via stale ACL

Published Feb 27, 2025 · Updated Sep 8, 2026

Use-after-free in Linux kernel nfsd allows remote attackers to disclose kernel memory or crash the host through NFSACL GETACL requests. An acl_default lookup failure releases both ACL objects but leaves acl_access pointing to freed posix_acl memory that nfs3svc_release_getacl later reuses and releases again. The path is reachable from a host permitted by an NFS export; panic-on-warning converts the refcount underflow into a kernel panic.

CVSS severity9.8
Critical
EPSS probability0.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in Linux kernel nfsd allows remote attackers to disclose kernel memory or crash the host through NFSACL GETACL requests. An acl_default lookup failure releases both ACL objects but leaves acl_access pointing to freed posix_acl memory that nfs3svc_release_getacl later reuses and releases again. The path is reachable from a host permitted by an NFS export; panic-on-warning converts the refcount underflow into a kernel panic.

The record

CVE
CVE-2025-21796
Published
Feb 27, 2025
Updated
Sep 8, 2026
Vendor
Siemens
Product
SIPLUS S7-1500 CPU 1518-4 PN/DP MFP
Classifications
CWE-416, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 27, 2025CVE publishedPublication date reported by the CVE source.
  2. Sep 8, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=V3.1.5 <*
  2. Affected versionversion=V3.1.6 <*

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Siemens · SIPLUS S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.5 <*; version=V3.1.6 <*
Siemens · SIMATIC S7-1500 TM MFP - GNU/Linux subsystemversion=0 <*
The Linux Kernel Organization · Linuxversion=2.6.13; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <1fd94884174bd20beb1773990fd3b1aa877688d9; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <2e59b2b68782519560b3d6a41dd66a3d01a01cd3; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <55d947315fb5f67a35e4e1d3e01bb886b9c6decf; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <6f7cfee1a316891890c505563aa54f3476db52fd; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <7faf14a7b0366f153284db0ad3347c457ea70136; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <8a1737ae42c928384ab6447f6ee1a882510e85fa; version=a257cdd0e2179630d3201c32ba14d7fcb3c3a055 <f8d871523142f7895f250a856f8c4a4181614510
Siemens · SIMATIC S7-1500 CPU 1518F-4 PN/DP MFPversion=V3.1.5 <*; version=V3.1.6 <*
Siemens · SIMATIC S7-1500 CPU 1518-4 PN/DP MFPversion=V3.1.5 <*; version=V3.1.6 <*

Published CVSS scores

9.8kernel.orgCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
7.8Siemens ProductCERTCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
7.8CISA-ADPCVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1499.004Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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