# CVE-2021-3838: PHAR Deserialization in dompdf/dompdf

> An attacker can achieve remote code execution by uploading a malicious PHAR file and triggering deserialization via the phar:// protocol in dompdf.

- **Severity:** Critical 9.8 (`CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 15 Nov 2024
- **Updated:** 18 Nov 2024
- **Also known as:** DEBIAN-CVE-2021-3838, DLA-3495-2, GHSA-577p-7j7h-2jgf, UBUNTU-CVE-2021-3838

## What is CVE-2021-3838?

CVE-2021-3838 is a critical unsafe deserialization vulnerability in dompdf/dompdf, published on 15 Nov 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

DomPDF before version 2.0.0 is vulnerable to PHAR deserialization due to a lack of checking on the protocol before passing it into the file_get_contents() function. An attacker who can upload files of any type to the server can pass in the phar:// protocol to unserialize the uploaded file and instantiate arbitrary PHP objects. This can lead to remote code execution, especially when DOMPdf is used with frameworks with documented POP chains like Laravel or vulnerable developer code.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2021-3838?

2 open source packages ship an affected version, including dompdf/dompdf. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `dompdf/dompdf` | Packagist | All versions | 2.0.0 |
| `dompdf/dompdf` | Packagist | All versions | 2.0.0 |

Products: Dompdf Project Dompdf.

## How do I fix CVE-2021-3838?

Upgrade dompdf/dompdf to 2.0.0 or later.

## Is CVE-2021-3838 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-3838 exists.

## Other vulnerabilities in dompdf/dompdf

- [CVE-2023-24813](https://insights.sbomify.com/CVE-2023-24813/): URI validation failure on SVG parsing. Bypass of CVE-2023-23924 (critical 10.0)
- [CVE-2023-23924](https://insights.sbomify.com/CVE-2023-23924/): URI validation failure on SVG parsing in Dompdf (critical 10.0)
- [CVE-2021-3902](https://insights.sbomify.com/CVE-2021-3902/): Improper Restriction of XML External Entity Reference in dompdf/dompdf (critical 9.8)
- [CVE-2022-28368](https://insights.sbomify.com/CVE-2022-28368/): Remote code injection in dompdf/dompdf (critical 9.8)
- [CVE-2014-5013](https://insights.sbomify.com/CVE-2014-5013/): DOMPDF Remote Code Execution (high 8.8)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-3838 and fix it if it is affected.

What it is: CVE-2021-3838 is a critical unsafe deserialization vulnerability in dompdf/dompdf, published on 15 Nov 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-3838 exists.

Affected packages and fixed versions:
- dompdf/dompdf (Packagist): affected all versions; fixed in 2.0.0
- dompdf/dompdf (Packagist): affected all versions; fixed in 2.0.0

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-2021-3838/ (Markdown: https://insights.sbomify.com/CVE-2021-3838/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3838
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3838
- OSV: https://osv.dev/vulnerability/CVE-2021-3838

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3838/
Summaries are generated and may contain mistakes; the official description above is the record.