TIRESIS/Forecast/CVE-2021-26091
MEDIUM RISK

CVE-2021-26091

A use of a cryptographically weak pseudo-random number generator vulnerability in the authenticator of the Identity Based Encryption service of FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to infer parts of users authentication toke…

SMB Attack Probability Score
24/100medium
Weighted: EPSS · CISA KEV · SMB stack prevalence · exploit maturity · CVSS vector
CVSS v3
7.5
EPSS (30d)
0.15%
SMB Exposure
46/100
Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
🔓
SMB Impact
How this vulnerability affects a real small business
1
How this breaks an SMB

Firewall or VPN compromise gives attackers full internal network access — no further credentials needed. All connected systems are immediately at risk.

2
Typical real-world scenario

Automated scanner identifies the exposed appliance. Within hours, lateral movement begins: file servers, domain controller, and backup systems are reached.

3
Estimated downtime & cost
Est. downtime
3–7 days
Business cost range
€15K–€80K
4
What IT should check this week
Is this appliance directly internet-facing?
Is firmware/OS version patched to latest?
Are admin consoles accessible without MFA?
Is network segmentation between IT and OT/servers active?
Scenarios are generated based on software category and CVE characteristics. Cost ranges reflect SMB incidents in TIRESIS incident database.
Threat Evolution Timeline
From disclosure to predicted exploitation — 3 events
◈ 1 predicted
📋
24 Mar 2025
Vulnerability disclosed
CVE published by NVD with CVSS 7.5 (HIGH)
📍
TODAY
Today
EPSS: 0.1% probability of exploitation in next 30 days. SMB Risk Score: 24/100
Forecast →
✅
29 Jun 2026◈ predicted · in 60 days
Predicted: widespread patch adoption
Low EPSS suggests limited active exploitation. Most organizations expected to patch in routine maintenance cycle.
◈ Predicted eventsare estimates based on EPSS score, exploit maturity, and historical CVE progression patterns. They are not guaranteed outcomes.
Affected Products
fortimail
Remediation & References
What to do
🌐No authentication required — restrict external access nowhigh

This vulnerability can be exploited remotely without credentials or user interaction. Until patched: block access to the affected service from the internet using firewall rules or ACLs. Only allow access from trusted IPs.

NVD Full Entry ↗Official vulnerability detail, CVSS vectors, CPE listEPSS Score ↗Exploit Prediction Scoring System — FIRST.orgMitre CVE ↗MITRE CVE Program official entry
Vendor & Exploit References
Scoring Methodology

SMB Attack Probability Score weights: EPSS exploit likelihood (35%), CISA KEV active exploitation (25%), SMB stack prevalence (20%), exploit maturity (10%), CVSS network vector complexity (10%). Impact scenarios are derived from software category and historical SMB incident patterns. Scores recompute daily.