# CVE-2021-24020: Weak cryptography in Fortinet FortiMail

> An unauthenticated attacker can bypass signature verification on signed URLs in FortiMail due to a missing cryptographic step, allowing data tampering.

- **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 9 Jul 2021
- **Updated:** 25 Oct 2024
- **Also known as:** GHSA-8wr8-gr7j-v6cg

## What is CVE-2021-24020?

CVE-2021-24020 is a high-severity vulnerability in Fortinet FortiMail, published on 9 Jul 2021. Any signed-in user can exploit it over the network, with no action from the victim.

### Official description

A missing cryptographic step in the implementation of the hash digest algorithm in FortiMail 6.4.0 through 6.4.4, and 6.2.0 through 6.2.7 may allow an unauthenticated attacker to tamper with signed URLs by appending further data which allows bypass of signature verification.

Weakness: CWE-347 (Improper Verification of Cryptographic Signature)

## Which versions are affected by CVE-2021-24020?

It affects 1 product.


Products: Fortinet Fortimail.

## How do I fix CVE-2021-24020?

No fix has been published for CVE-2021-24020 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-24020 being exploited?

There is no known exploitation of CVE-2021-24020 in the wild and no public exploit code.

## Other vulnerabilities in Fortinet FortiMail

- [CVE-2026-104286](https://insights.sbomify.com/CVE-2026-104286/): Fortinet FortiMail Path Traversal (critical 9.8, exploited in the wild)
- [CVE-2021-36166](https://insights.sbomify.com/CVE-2021-36166/): Auth bypass in Fortinet FortiMail (critical 9.8)
- [CVE-2021-24007](https://insights.sbomify.com/CVE-2021-24007/): SQL injection in Fortinet FortiMail (critical 9.8)
- [CVE-2020-9294](https://insights.sbomify.com/CVE-2020-9294/): Auth bypass in FortiMail (critical 9.8)
- [CVE-2023-47539](https://insights.sbomify.com/CVE-2023-47539/): Auth bypass in FortiMail (critical 9.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-24020 and fix it if it is affected.

What it is: CVE-2021-24020 is a high-severity vulnerability in Fortinet FortiMail, published on 9 Jul 2021. Any signed-in user can exploit it over the network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-24020 in the wild and no public exploit code.

Affected product: Fortinet FortiMail. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-24020/ (Markdown: https://insights.sbomify.com/CVE-2021-24020/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-24020
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-24020
- OSV: https://osv.dev/vulnerability/CVE-2021-24020

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-24020/
Summaries are generated and may contain mistakes; the official description above is the record.