# CVE-2021-32816: Regular expression Denial of Service in ProtonMail

> An attacker can cause a denial of service in the ProtonMail web client by exploiting a regular expression vulnerability.

- **Severity:** Medium 6.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** No
- **Published:** 14 May 2021
- **Updated:** 3 Aug 2024
- **Also known as:** GHSA-h97j-5ccr-wj2x

## What is CVE-2021-32816?

CVE-2021-32816 is a medium-severity denial of service vulnerability in ProtonMail WebClient, published on 14 May 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official description

ProtonMail Web Client is the official AngularJS web client for the ProtonMail secure email service. ProtonMail Web Client before version 3.16.60 has a regular expression denial-of-service vulnerability. This was fixed in commit 6687fb. There is a full report available in the referenced GHSL-2021-027.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-32816?

It affects 1 product.


Products: Protonmail Protonmail.

## How do I fix CVE-2021-32816?

No fix has been published for CVE-2021-32816 yet. Limit exposure of the affected software until one is available.

## Is CVE-2021-32816 being exploited?

There is no known exploitation of CVE-2021-32816 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-32816 and fix it if it is affected.

What it is: CVE-2021-32816 is a medium-severity denial of service vulnerability in ProtonMail WebClient, published on 14 May 2021. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2021-32816 in the wild and no public exploit code.

Affected product: ProtonMail WebClient. 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-2021-32816/ (Markdown: https://insights.sbomify.com/CVE-2021-32816/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-32816
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-32816
- OSV: https://osv.dev/vulnerability/CVE-2021-32816

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-32816/
Summaries are generated and may contain mistakes; the official description above is the record.