# CVE-2026-59840 — Fortinet FortiOS

> As of 2026-08-11, CVE-2026-59840 is a MEDIUM-severity vulnerability in Fortinet FortiOS, CVSS v3.1 4.1, EPSS 0.3% (22.2th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2026-59840, most recently “Multiple Vulnerabilities in Fortigate NGFW on RUGGEDCOM APE1808 Devices (SSA-864900) — Including Actively Exploited FortiCloud SSO Bypass (CVE-2025-59718/-59719) and FortiOS Heap Overflow (CVE-2025-25249)”.

**Last updated:** 2026-08-11

## What is CVE-2026-59840?

A buffer over-read vulnerability in Fortinet FortiOS 7.6.0 through 7.6.3, FortiOS 7.4.0 through 7.4.8, FortiOS 7.2 all versions, FortiOS 7.0 all versions, FortiOS 6.4 all versions, FortiProxy 7.6.0 through 7.6.5, FortiProxy 7.4.0 through 7.4.13, FortiProxy 7.2 all versions, FortiProxy 7.0 all versions may allow attacker to information disclosure via

The record classifies CVE-2026-59840 under weakness class [CWE-126](https://intel.threadlinqs.com/cwe/CWE-126). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction. 4 affected-product entries are recorded, across 1 vendor, listed below. The identifier was first published 89 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 4.1 — MEDIUM (`CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:L/I:N/A:N/E:P/RL:O/RC:C`)
- **EPSS (FIRST):** 0.3% probability of exploitation in the next 30 days, higher than 22.2% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 2.9/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2026-07-14, last modified 2026-08-11

## Is CVE-2026-59840 being exploited?

It currently carries a trending score of 19 in the Threadlinqs vulnerability feed.

## Affected products and versions

- [Fortinet](https://intel.threadlinqs.com/vendors/fortinet): FortiOS, FortiPAM, FortiSwitchManager, FortiProxy

## How to fix CVE-2026-59840

No vendor patch reference has been recorded for CVE-2026-59840 in the tracked sources. Follow the references below for a fix, and treat the products listed above as exposed until the vendor states otherwise.

## Threat activity tracking CVE-2026-59840

1 tracked threat in the Threadlinqs corpus references CVE-2026-59840, either in the campaign’s CVE list or as an indicator on the campaign record.

- [Multiple Vulnerabilities in Fortigate NGFW on RUGGEDCOM APE1808 Devices (SSA-864900) — Including Actively Exploited FortiCloud SSO Bypass (CVE-2025-59718/-59719) and FortiOS Heap Overflow (CVE-2025-25249)](https://intel.threadlinqs.com/threat/TL-2026-2486) — CRITICAL · 2026-09-13

## Sources

Enriched from CVE.org, FIRST EPSS. Last verified by Threadlinqs on 2026-10-10.

**Other references**

- [fortiguard.fortinet.com](https://fortiguard.fortinet.com/psirt/FG-IR-26-154)

Canonical: https://intel.threadlinqs.com/cve/CVE-2026-59840
Full detection coverage and IOCs for threats exploiting CVE-2026-59840 via the Threadlinqs MCP server (Purple tier): https://intel.threadlinqs.com/mcp