VulnerabilityPublished 1 Apr 2025Updated 31 Oct 2025

CVE-2025-21902: Linux kernel · acpi: typec: ucsi: Introduce a ->poll_cci method

Source GCVE Database

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Not known to be exploited · CVSS 5.5 Medium.

Data as of 29 Oct 2026, 23:34 UTC

CVSS 3.1 base score

5.5Medium

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

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

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

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: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 1 Apr 2025
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: 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 29 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.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), 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.

ghsa-w69j-ppp7-83pp

What to do

AI-suggested

A fix has been implemented in the Linux kernel by introducing the ->poll_cci() method to handle register synchronization correctly when notifications are disabled. Users should update to the Linux kernel version that includes this fix. Since the advisory does not provide explicit patch versions, check the vendor or kernel release notes for the fixed version. No additional mitigations are required beyond applying the official fix.

Description

CVE-2025-21902 addresses a vulnerability in the Linux kernel's ACPI backend for UCSI (USB Type-C Connector System Software Interface). The issue involves improper handling of register synchronization between the embedded controller and the ACPI opregion, which can cause spurious kernel warnings and potential instability when polling the CCI register with notifications disabled. The vulnerability is mitigated by introducing a new ->poll_cci() method that forces synchronization safely under these conditions.

Impact

The vulnerability can cause kernel warnings and assertion failures leading to potential denial of service through kernel instability or crashes. The CVSS score of 5.5 (medium severity) reflects that the impact is limited to availability (A:H) without confidentiality or integrity loss. There is no indication of exploitation in the wild or direct compromise of data.

Summary

This vulnerability in the Linux kernel's ACPI backend for UCSI arises because the UCSI registers are memory copies of register values in an ACPI opregion. The BIOS ensures synchronization between the embedded controller and the opregion, but forcing a sync from the embedded controller when notifications are disabled can cause kernel assertion failures and warnings. The fix introduces a dedicated ->poll_cci() method that performs a forced sync only when necessary, avoiding the spurious assertion splats and improving stability. This method is used specifically when polling with notifications disabled, while other backends continue using the same implementation for both polling and reading CCI.

References

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