# CVE-2025-53843 — Fortinet FortiOS

> As of 2026-09-13, CVE-2025-53843 is a MEDIUM-severity vulnerability in Fortinet FortiOS, CVSS v3.1 6.9, EPSS 0.5% (46.5th percentile). Threadlinqs Intelligence links 1 tracked threat campaign to CVE-2025-53843, 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-2025-53843?

A stack-based buffer overflow 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 allows attacker to execute unauthorized code or commands via specially crafted packets

The record classifies CVE-2025-53843 under weakness class [CWE-121](https://intel.threadlinqs.com/cwe/CWE-121). Its CVSS v3 base vector states that the flaw is reachable remotely over the network, needs low-privilege credentials, needs no user interaction, and has high impact on confidentiality, integrity, availability. 1 affected-product entry is recorded, across 1 vendor, listed below. The identifier was first published 353 days ago.

## Severity and exploitation probability

- **CVSS v3.1 base score:** 6.9 — MEDIUM (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:P/RL:W/RC:C`)
- **EPSS (FIRST):** 0.5% probability of exploitation in the next 30 days, higher than 46.5% of all scored CVEs
- **CISA KEV:** Not listed in the CISA Known Exploited Vulnerabilities catalog
- **Threadlinqs priority:** 5.3/10 — a Threadlinqs composite of the CVSS base score, the EPSS percentile and public exploit availability
- **Published:** 2025-11-18, last modified 2026-08-11

## Is CVE-2025-53843 being exploited?

It currently carries a trending score of 17 in the Threadlinqs vulnerability feed.

## Affected products and versions

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

## How to fix CVE-2025-53843

No vendor patch reference has been recorded for CVE-2025-53843 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-2025-53843

1 tracked threat in the Threadlinqs corpus references CVE-2025-53843, 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-25-358)

Canonical: https://intel.threadlinqs.com/cve/CVE-2025-53843
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