CVE-2026-99040

Restriction bypass via stale keyring restriction snapshot

Published Oct 23, 2026 · Updated Oct 23, 2026

A race in Linux keyring creation allows local users to bypass reject-all restrictions via concurrent add_key() and restriction calls. __key_create_or_update() reads keyring->restrict_link before acquiring the destination semaphore, then links an attacker-supplied key using a stale NULL snapshot after restriction installation completes. Exploitation requires write permission on the destination keyring and winning the race; the demonstrated consequence is insertion of a prohibited key, not arbitrary code execution.

CVSS severityUnavailable
Unscored
EPSS probability0.19%
Next 30 days · Nov 1, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

A race in Linux keyring creation allows local users to bypass reject-all restrictions via concurrent add_key() and restriction calls. __key_create_or_update() reads keyring->restrict_link before acquiring the destination semaphore, then links an attacker-supplied key using a stale NULL snapshot after restriction installation completes. Exploitation requires write permission on the destination keyring and winning the race; the demonstrated consequence is insertion of a prohibited key, not arbitrary code execution.

The record

CVE
CVE-2026-99040
Published
Oct 23, 2026
Updated
Oct 23, 2026
Vendor
The Linux Kernel Organization
Product
Linux
Classifications
Unavailable
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Oct 23, 2026CVE publishedPublication date reported by the CVE source.
  2. Oct 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=4.7
  2. Affected versionversion=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <11516a0c402a6c1fa52254aa70d8d65fb921e59e
  3. Affected versionversion=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <305f1828b871dd46bf41addeb6f11d2c162dcb25
  4. Affected versionversion=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <da0b595d8e6e2dd798f6e34e09dc51a13b888514
  5. Affected versionversion=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <dd3ea3fcba7c75493760cdbccd35f029597e8d5e
  6. Affected versionversion=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <f99399b48e3edd6851fac34cd329bab9f1f33baf

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The Linux Kernel Organization · Linuxversion=4.7; version=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <11516a0c402a6c1fa52254aa70d8d65fb921e59e; version=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <305f1828b871dd46bf41addeb6f11d2c162dcb25; version=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <da0b595d8e6e2dd798f6e34e09dc51a13b888514; version=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <dd3ea3fcba7c75493760cdbccd35f029597e8d5e; version=5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c <f99399b48e3edd6851fac34cd329bab9f1f33baf

Published CVSS scores

No CVSS assessment is available in this record.

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.

Activity data is delayed. The latest report is Sep 28, 2026.

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

No observations available

Sep 22, 2026Sep 28, 2026
Latest reporting daySep 28, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

No sourced classifications are available.

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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