CVE-2021-42756 Memory corruption in FortiWeb

What is CVE-2021-42756?

CVE-2021-42756 is a critical memory corruption vulnerability in Fortinet Fortiweb, published on 16 Feb 2023. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official 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.

Weakness: CWE-787, CWE-121

Which versions are affected by CVE-2021-42756?

It affects 1 product.

Products include Fortinet Fortiweb.

How do I fix CVE-2021-42756?

No fix has been published for CVE-2021-42756 yet. Limit exposure of the affected software until one is available.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2021-42756 being exploited?

There is no known exploitation of CVE-2021-42756 in the wild and no public exploit code.

Public exploit code: 1 proofs of concept on GitHub.

Other vulnerabilities in Fortinet Fortiweb

• CVE-2025-25257 Fortinet FortiWeb SQL Injection Exploited Critical 9.6
• CVE-2025-64446 Fortinet FortiWeb Path Traversal Exploited Critical 9.4
• CVE-2025-58034 Fortinet FortiWeb OS Command Injection Exploited Medium 6.7
• CVE-2020-29015 SQL injection in Fortinet FortiWeb Critical 9.8
• CVE-2020-29016 Memory corruption in Fortinet FortiWeb Critical 9.8

All Fortinet Fortiweb vulnerabilities

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as GHSA-wqmg-f43p-5ccf.