Buffer Over-Read in Fortinet FortiOS and FortiProxy

Executive Summary

CVE-2026-59840 is a buffer over-read vulnerability affecting Fortinet FortiOS and FortiProxy products. A buffer over-read occurs when a program reads more data from a buffer than what is allocated, potentially exposing sensitive information.

This vulnerability exists in multiple versions of Fortinet FortiOS (7.6.0 through 7.6.2, 7.4.0 through 7.4.8, and all 7.2 versions) and FortiProxy (7.6.0 through 7.6.5, 7.4.0 through 7.4.13, and all 7.2 versions). An attacker may exploit this flaw to disclose information, though the specific attack vector is not detailed in the provided context.

The CVSS v3.1 base score for this vulnerability is 4.3, indicating a medium severity. The vector (AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N) means it can be exploited over a network with low attack complexity, requires low privileges, and does not need user interaction. The impact is limited to confidentiality, with no integrity or availability impact.

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Detection Guidance

The provided CVE data does not include specific detection methods or commands for identifying the buffer over-read vulnerability in Fortinet FortiOS and FortiProxy. Detection typically involves checking the installed versions of FortiOS or FortiProxy against the affected versions listed in the CVE description.

• Verify the version of FortiOS or FortiProxy running on your devices. The affected versions are:
• FortiOS: 7.6.0 through 7.6.2, 7.4.0 through 7.4.8, and all versions of 7.2.
• FortiProxy: 7.6.0 through 7.6.5, 7.4.0 through 7.4.13, and all versions of 7.2.

You can check the version by logging into the Fortinet device's CLI and running the following command:

• For FortiOS: get system status | grep Version
• For FortiProxy: get system status | grep Version

If the installed version matches any of the affected versions, the system may be vulnerable.

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Impact Analysis

If you are using an affected version of Fortinet FortiOS or FortiProxy, this vulnerability could impact you in the following ways:

• Information disclosure: An attacker may exploit the buffer over-read to access sensitive data stored or processed by the affected system. This could include configuration details, credentials, or other confidential information.
• Unauthorized access: If the disclosed information includes authentication details or session tokens, an attacker might use it to gain unauthorized access to your network or systems.
• Potential for further attacks: The information obtained could be used as a stepping stone for more severe attacks, such as lateral movement within your network or targeted exploitation of other vulnerabilities.

The vulnerability requires low privileges to exploit, meaning even users with limited access could potentially trigger it. However, the impact is primarily on confidentiality, so the risk of system crashes or data corruption is low.

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Compliance Impact

This vulnerability could affect compliance with several common standards and regulations, depending on the nature of the data processed or stored by the affected systems:

• GDPR (General Data Protection Regulation): If the disclosed information includes personal data of EU citizens, this vulnerability could lead to a data breach. GDPR requires organizations to implement appropriate security measures to protect personal data. Failure to patch or mitigate this vulnerability could result in non-compliance, potentially leading to fines or legal action.
• HIPAA (Health Insurance Portability and Accountability Act): If the affected system processes or stores protected health information (PHI), this vulnerability could result in unauthorized disclosure of PHI. HIPAA mandates safeguards to protect PHI, and a breach could lead to penalties for non-compliance.
• PCI DSS (Payment Card Industry Data Security Standard): If the system handles payment card data, this vulnerability could expose sensitive cardholder information. PCI DSS requires organizations to maintain a secure environment for processing payment data, and a breach could result in non-compliance and potential fines.

Organizations should assess whether the affected systems process regulated data and take appropriate steps to mitigate the vulnerability to maintain compliance. This may include applying patches, implementing compensating controls, or isolating affected systems until a fix is available.

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Mitigation Strategies

The provided CVE data does not include specific mitigation steps, but general best practices for addressing such vulnerabilities in Fortinet products include the following:

• Upgrade to the latest patched version of FortiOS or FortiProxy as soon as it is available from Fortinet. This is the most effective way to mitigate the vulnerability.
• If upgrading is not immediately possible, apply any available workarounds or interim fixes provided by Fortinet in their security advisories.
• Restrict network access to the Fortinet management interface to trusted IP addresses only, reducing the attack surface.
• Monitor network traffic for unusual activity that may indicate exploitation attempts, such as unexpected data exfiltration.
• Review Fortinet's official security advisories for this CVE (when available) for additional guidance or patches.

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