VulnerabilityPublished 17 Sep 2026Updated 21 Oct 2026

CVE-2026-90231: Linux kernel · apparmor: fix unconfined user namespace restriction forced stack

Affects Linux kernelSource CVE Database V5

Not known to be exploited · CVSS 8.4 High · fixed in fdd341654471cae4fbd9635d32b848cd0c8bc437 : patch Linux kernel soon.

Data as of 26 Oct 2026, 13:47 UTC

CVSS 3.1 base score

8.4High

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.1% chance of exploitation in 30 days – higher than 6% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in fdd341654471cae4fbd9635d32b848cd0c8bc437, 08c2f7c8d4b1434cfae006f3daf4d1bce330b57b, 7da0bdf0610f6d35bbb061536a47fc41646306f0 +1

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

Attack Vector: Local
Attack Complexity: Low
Privileges Required: Low
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Local: The vulnerable component is not bound to the network stack and the attacker’s path is via read/write/execute capabilities. Either: the attacker exploits the vulnerability by accessing the target system locally (e.g., keyboard, console), or remotely (e.g., SSH); or the attacker relies on User Interaction by another person to perform actions required to exploit the vulnerability (e.g., tricking a legitimate user into opening a malicious document).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: Low: The attacker is authorized with (i.e., requires) privileges that provide basic user capabilities that could normally affect only settings and files owned by a user. Alternatively, an attacker with Low privileges may have the ability to cause an impact only to non-sensitive resources.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 17 Sep 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 Linux kernel to fdd341654471cae4fbd9635d32b848cd0c8bc437, 08c2f7c8d4b1434cfae006f3daf4d1bce330b57b, 7da0bdf0610f6d35bbb061536a47fc41646306f0 or 7d1099b86356df81c379159bfb8a598aaf83ce81.

Affected software

Product	Affected	Fixed in
LinuxLinux	Affected ≥ 2d9da9b188b8cd3b579d7ef5ba5d334be9dd38fc, < fdd341654471cae4fbd9635d32b848cd0c8bc437	Fixed in fdd341654471cae4fbd9635d32b848cd0c8bc437
LinuxLinux	Affected ≥ 2d9da9b188b8cd3b579d7ef5ba5d334be9dd38fc, < 08c2f7c8d4b1434cfae006f3daf4d1bce330b57b	Fixed in 08c2f7c8d4b1434cfae006f3daf4d1bce330b57b
LinuxLinux	Affected ≥ 2d9da9b188b8cd3b579d7ef5ba5d334be9dd38fc, < 7da0bdf0610f6d35bbb061536a47fc41646306f0	Fixed in 7da0bdf0610f6d35bbb061536a47fc41646306f0
LinuxLinux	Affected ≥ 2d9da9b188b8cd3b579d7ef5ba5d334be9dd38fc, < 7d1099b86356df81c379159bfb8a598aaf83ce81	Fixed in 7d1099b86356df81c379159bfb8a598aaf83ce81
LinuxLinux	Affected =6.7	Fixed in–

Description

In the Linux kernel, the following vulnerability has been resolved: apparmor: fix unconfined user namespace restriction forced stack If a task is already confined by a stack the unprivileged transition restriction on unconfined is not correctly, applied. This results in an escape if two transitions through an unconfined profile can be executed. Fix this by pushing the check into the per profile label build. The check will always be done against unconfined and result in a stack of just the unconfined component when necessary.

References

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