VulnerabilityPublished 23 Oct 2026

CVE-2026-99040: Linux kernel · KEYS: Fix add_key() race with keyring restriction

Affects Linux kernelSource CVE Database V5

Not known to be exploited · fixed in f99399b48e3edd6851fac34cd329bab9f1f33baf : patch Linux kernel soon.

Data as of 26 Oct 2026, 14:18 UTC

Severity

High

Rated High by Threat Radar's AI analysis · CVSS not yet scored by NVD

EPSS: 0.1% chance of exploitation in 30 days – higher than 7% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in f99399b48e3edd6851fac34cd329bab9f1f33baf, dd3ea3fcba7c75493760cdbccd35f029597e8d5e, da0b595d8e6e2dd798f6e34e09dc51a13b888514 +2

Exploitation evidence

Disclosed: evidence found.
CVE published 23 Oct 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponised: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 26 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponised: Public exploit code exists in Metasploit or Exploit-DB, or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade to a fixed release listed under Affected software.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < f99399b48e3edd6851fac34cd329bab9f1f33baf	Fixed in f99399b48e3edd6851fac34cd329bab9f1f33baf
LinuxLinux	Affected ≥ 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < dd3ea3fcba7c75493760cdbccd35f029597e8d5e	Fixed in dd3ea3fcba7c75493760cdbccd35f029597e8d5e
LinuxLinux	Affected ≥ 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < da0b595d8e6e2dd798f6e34e09dc51a13b888514	Fixed in da0b595d8e6e2dd798f6e34e09dc51a13b888514
LinuxLinux	Affected ≥ 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 11516a0c402a6c1fa52254aa70d8d65fb921e59e	Fixed in 11516a0c402a6c1fa52254aa70d8d65fb921e59e
LinuxLinux	Affected ≥ 5ac7eace2d00eab5ae0e9fdee63e38aee6001f7c, < 305f1828b871dd46bf41addeb6f11d2c162dcb25	Fixed in 305f1828b871dd46bf41addeb6f11d2c162dcb25
LinuxLinux	Affected =4.7	Fixed in–

AI-suggested

The vulnerability has been fixed in the Linux kernel. Users should apply the official patches or upgrade to a fixed kernel version containing the commits identified (e.g., f99399b48e3e and others). No additional mitigation is required once the fix is applied.

Description

A race condition vulnerability in the Linux kernel's key management subsystem was fixed. The flaw allowed a writer with write permission on a destination keyring to bypass keyring restrictions by exploiting a timing issue in add_key() operations. This could result in keys being linked despite a reject-all restriction. The issue was confirmed through extensive testing and was resolved by reordering the restriction check to ensure proper synchronization.

Impact

An attacker with write permission on a destination keyring could bypass keyring restrictions and link keys despite a reject-all restriction being in place. This undermines the intended access control and could lead to unauthorized key associations within the kernel's key management system. There is no indication of known exploitation in the wild.

Summary

CVE-2026-99040 addresses a race condition in the Linux kernel's key management system where __key_create_or_update() took a snapshot of keyring->restrict_link before acquiring the destination keyring's semaphore. This allowed a writer to observe no restriction, wait for the keyring owner to install a reject-all restriction, and then link a key using a stale NULL snapshot, bypassing the restriction. The vulnerability requires only write permission on the destination keyring. The fix moves the restrict_link read after __key_link_lock() and __key_link_begin(), ensuring serialization with restriction installation via the keyring semaphore. The race was reproducible on version 4.7, with tests showing successful unauthorized key linking before the fix and consistent failure after the fix.

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 26 Oct 2026, 09:58 UTC

Technical details

References

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