What’s Vulnerable › Vulnerabilities

CVE-2021-42756

• Severity: critical (CVSS 9.8 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 35.0% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2023-02-16 · updated 2026-06-17
• Weakness: CWE-121

Description

Multiple stack-based buffer overflow vulnerabilities [CWE-121] in the proxy daemon of FortiWeb 5.x all versions, 6.0.7 and below, 6.1.2 and below, 6.2.6 and below, 6.3.16 and below, 6.4 all versions may allow an unauthenticated remote attacker to achieve arbitrary code execution via specifically crafted HTTP requests.

Affected products

• Fortinet FortiWeb: from 5.6.0 before 6.0.8; from 6.1.0 before 6.1.3; from 6.2.0 before 6.2.7; from 6.3.0 before 6.3.17; from 6.4.0 through 6.4.2 — fixed in 6.0.8, 6.1.3, 6.2.7, 6.3.17

How to fix

Upgrade to a fixed version: Fortinet FortiWeb 6.0.8, 6.1.3, 6.2.7, 6.3.17. Check the vendor advisory for mitigations.

References

• https://fortiguard.com/psirt/FG-IR-21-186
• https://fortiguard.com/psirt/FG-IR-21-186

Get alerted when CVE-2021-42756 or the next vulnerability affects your stack