Critical severity · published Feb 16, 2023
CVE-2021-42756
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…
9.8
CVSS
35%
EPSS
No
On KEV
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.
CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
Attack vector
Network
Complexity
Low
Privileges
None
User interaction
None
Confidentiality
High
Integrity
High
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)35.0% · higher than 98% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
FO
Fortiweb · Fortinet
5.6.0 before 6.0.8; 6.1.0 before 6.1.3; 6.2.0 before 6.2.7; 6.3.0 before 6.3.17; 6.4.0 through 6.4.2 · source: NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2021-42756
CVE.org
https://www.cve.org/CVERecord?id=CVE-2021-42756
Vendor Advisory
https://fortiguard.com/psirt/FG-IR-21-186
More from Fortiweb
9.8
CVE-2026-24858
Fortinet Multiple Products Authentication Bypass Using an Alternate Path or Channel Vulnerability
9.8
CVE-2025-64446
Fortinet FortiWeb Path Traversal Vulnerability
9.8
CVE-2025-25257
Fortinet FortiWeb SQL Injection Vulnerability
7.2
CVE-2025-58034
Fortinet FortiWeb OS Command Injection Vulnerability
9.8
CVE-2026-26035
An Improper Authentication vulnerability [CWE-287] vulnerability in Fortinet FortiWeb 8.0.0 through 8.0.2, FortiWeb 7.6.0 through 7.6.6, FortiWeb 7.4.0 through 7.4.11, FortiWeb…