# CVE-2021-23980: Cross-site scripting in Bleach

> Mutation XSS in Bleach allows code execution when specific non-default tags and settings are used for HTML sanitization.

- **Severity:** Medium 6.1 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N`)
- **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:** Yes
- **Published:** 16 Feb 2023
- **Updated:** 19 Mar 2025
- **Also known as:** DEBIAN-CVE-2021-23980, DLA-2620-1, DSA-4892-1, GHSA-vv2x-vrpj-qqpq, MGASA-2021-0260, OESA-2022-1861, PYSEC-2021-865, UBUNTU-CVE-2021-23980

## What is CVE-2021-23980?

CVE-2021-23980 is a medium-severity cross-site scripting vulnerability in Mozilla Bleach, published on 16 Feb 2023. 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

A mutation XSS affects users calling bleach.clean with all of: svg or math in the allowed tags p or br in allowed tags style, title, noscript, script, textarea, noframes, iframe, or xmp in allowed tags the keyword argument strip_comments=False Note: none of the above tags are in the default allowed tags and strip_comments defaults to True.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation)

## Which versions are affected by CVE-2021-23980?

3 open source packages ship an affected version, including bleach. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `bleach` | PyPI | All versions | 3.3.0 |
| `bleach` | PyPI | All versions | 3.3.0 |
| `bleach` | PyPI | All versions | 3.3.0 |

Products: Mozilla Bleach.

## How do I fix CVE-2021-23980?

Upgrade bleach to 3.3.0 or later.

## Is CVE-2021-23980 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-23980 exists.

## Other vulnerabilities in Mozilla Bleach

- [CVE-2018-7753](https://insights.sbomify.com/CVE-2018-7753/): Bleach URI Scheme Restriction Bypass (critical 9.8)
- [CVE-2020-6817](https://insights.sbomify.com/CVE-2020-6817/): regular expression denial-of-service (ReDoS) in Bleach (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-23980 and fix it if it is affected.

What it is: CVE-2021-23980 is a medium-severity cross-site scripting vulnerability in Mozilla Bleach, published on 16 Feb 2023. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-23980 exists.

Affected packages and fixed versions:
- bleach (PyPI): affected all versions; fixed in 3.3.0
- bleach (PyPI): affected all versions; fixed in 3.3.0
- bleach (PyPI): affected all versions; fixed in 3.3.0

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-2021-23980/ (Markdown: https://insights.sbomify.com/CVE-2021-23980/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-23980
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-23980
- OSV: https://osv.dev/vulnerability/CVE-2021-23980

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-23980/
Summaries are generated and may contain mistakes; the official description above is the record.