CVE-2025-40206

Host crash via unvalidated synproxy OUTPUT reference

Published Nov 12, 2025 · Updated Aug 23, 2026

Denial of service in Linux nft_objref allows local users to crash the host by attaching a synproxy object to an nftables OUTPUT hook. nft_objref and objrefmap accept the SYNPROXY reference without validating hook compatibility, so a locally generated SYN recursively re-enters IPv6 output routing until the kernel stack is exhausted. A local user with low privileges can obtain namespace-scoped CAP_NET_ADMIN, install the rule, and cause a host-wide panic without interaction from another user.

CVSS severity7.8
High
EPSS probability0.14%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Linux nft_objref allows local users to crash the host by attaching a synproxy object to an nftables OUTPUT hook. nft_objref and objrefmap accept the SYNPROXY reference without validating hook compatibility, so a locally generated SYN recursively re-enters IPv6 output routing until the kernel stack is exhausted. A local user with low privileges can obtain namespace-scoped CAP_NET_ADMIN, install the rule, and cause a host-wide panic without interaction from another user.

The record

CVE
CVE-2025-40206
Published
Nov 12, 2025
Updated
Aug 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
T1499
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Nov 12, 2025CVE publishedPublication date reported by the CVE source.
  2. Aug 23, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

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

  1. Affected versionversion=5.4
  2. Affected versionversion=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <0028e0134c64d9ed21728341a74fcfc59cd0f944
  3. Affected versionversion=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <4c1cf72ec10be5a9ad264650cadffa1fbce6fabd
  4. Affected versionversion=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0
  5. Affected versionversion=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <f31bcea12222a26d6f151df9c4a6d21f2eec1724
  6. Affected versionversion=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <f359b809d54c6e3dd1d039b97e0b68390b0e53e4

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=5.4; version=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <0028e0134c64d9ed21728341a74fcfc59cd0f944; version=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <4c1cf72ec10be5a9ad264650cadffa1fbce6fabd; version=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <7ea55a44493a5a36c3b3293b88bbe4841f9dbaf0; version=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <f31bcea12222a26d6f151df9c4a6d21f2eec1724; version=ee394f96ad7517fbc0de9106dcc7ce9efb14f264 <f359b809d54c6e3dd1d039b97e0b68390b0e53e4

Published CVSS scores

7.8LinuxCVSS: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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

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

Weakness, pattern, technique

T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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