CVE-2025-4421VulnerabilityPublished 30 Jul 2025Updated 14 Aug 2025

CVE-2025-4421: Insyde Software InsydeH2O · Out-of-bounds Write

Affects Insyde Software InsydeH2OSource CVE Database V5

Not known to be exploited · CVSS 8.2 High.

Data as of 25 Oct 2026, 19:02 UTC

CVSS 3.1 base score

8.2High

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

EPSS: 0.2% chance of exploitation in 30 days – higher than 14% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.

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

Attack Vector: Local
Attack Complexity: Low
Privileges Required: High
User Interaction: None
Scope: Changed
Confidentiality: High
Integrity: High
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: High: The attacker is authorized with (i.e., requires) privileges that provide significant (e.g., administrative) control over the vulnerable component that could affect component-wide settings and files.
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: 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 30 Jul 2025
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 2026-10-25.

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 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

AI-suggested

European organizations should take proactive and specific steps beyond generic patching advice: 1) Inventory all Lenovo devices using InsydeH2O firmware to identify potentially affected systems. 2) Monitor Lenovo’s official Product Security Advisories closely for the release of patches or firmware updates addressing CVE-2025-4421. 3) Until patches are available, restrict local administrative access to trusted personnel only and implement strict access controls to minimize the risk of privilege escalation. 4) Employ endpoint detection and response (EDR) solutions capable of monitoring unusual firmware or kernel-level activity indicative of exploitation attempts. 5) Conduct firmware integrity checks and consider using hardware-based security features such as TPM and Secure Boot to detect unauthorized firmware modifications. 6) Educate IT staff and security teams about the vulnerability specifics to enhance incident response readiness. 7) For critical systems, consider temporary isolation or enhanced monitoring to reduce attack surface exposure. 8) Collaborate with Lenovo support for guidance and early access to mitigations if available.

Description

The vulnerability was identified in the code developed specifically for Lenovo. Please visit "Lenovo Product Security Advisories and Announcements" webpage for more information about the vulnerability. https://support.lenovo.com/us/en/product_security/home

Impact

For European organizations, this vulnerability poses a substantial risk due to the widespread use of Lenovo laptops and desktops in corporate, governmental, and critical infrastructure environments. Exploitation could allow attackers to gain kernel-level code execution or escalate privileges, leading to unauthorized access to sensitive data, disruption of business operations, or persistent footholds within networks. The confidentiality impact is high as attackers could access protected information; integrity is compromised through potential unauthorized code execution or firmware manipulation; availability could be affected by system crashes or denial-of-service conditions. Given the vulnerability requires local high privileges, insider threats or attackers who have already compromised user accounts could leverage this flaw to deepen their control. This is particularly concerning for sectors with strict data protection regulations like GDPR, where breaches can result in severe penalties. Additionally, the firmware-level nature of the vulnerability complicates detection and remediation, increasing the risk of prolonged exposure.

Summary

CVE-2025-4421 is a high-severity vulnerability classified as CWE-787, indicating an out-of-bounds write issue within Insyde Software's InsydeH2O firmware, specifically in a feature developed for Lenovo devices. InsydeH2O is a widely used UEFI BIOS firmware solution that initializes hardware and loads the operating system on many laptops and desktops. The vulnerability arises from improper bounds checking during memory operations, allowing an attacker with high privileges (PR:H) and local access (AV:L) to write data outside the intended memory buffer. This can lead to corruption of adjacent memory, potentially enabling privilege escalation, arbitrary code execution, or system instability. The CVSS 3.1 score of 8.2 reflects the critical impact on confidentiality, integrity, and availability, with a scope change (S:C) indicating that the vulnerability can affect components beyond the initially compromised privilege boundary. No user interaction is required (UI:N), but the attacker must have elevated privileges to exploit it. Although no known exploits are currently in the wild, the vulnerability's nature and impact make it a significant risk, especially for Lenovo devices using this specific InsydeH2O feature. The lack of publicly available patches at the time of publication necessitates urgent attention from affected organizations to monitor vendor advisories and prepare for remediation.

CWE-787Out-of-bounds Write (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #5
The product writes data past the end, or before the beginning, of the intended buffer.
Requirements · Language Selection
Use a language that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Architecture and Design · Libraries or Frameworks
Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
Operation · Build and Compilation · Environment Hardening
Use automatic buffer overflow detection mechanisms that are offered by certain compilers or compiler extensions. Examples include: the Microsoft Visual Studio /GS flag, Fedora/Red Hat FORTIFY_SOURCE GCC flag, StackGuard, and ProPolice, which provide various mechanisms including canary-based detection and range/index…
OWASP Cheat Sheets
XML Security (opens in a new tab)
Mass Assignment (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.1 (opens in a new tab)
V5.1.4 (opens in a new tab)
V5.1.3 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Description

AI analysisMachine-generated, updated 15 Aug 2025, 00:46 UTC

WeaknessesCWE-787

Technical details

References

Community reviews

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