# CVE-2021-3902: Improper Restriction of XML External Entity Reference in dompdf/dompdf

> Attackers can exploit an XXE flaw in the SVG parser to perform SSRF, disclose internal files, or trigger PHAR deserialization, even with remote features disabled.

- **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-2021-3902, GHSA-3vjh-xrhf-v9xh

## What is CVE-2021-3902?

CVE-2021-3902 is a critical 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

An improper restriction of external entities (XXE) vulnerability in dompdf/dompdf's SVG parser allows for Server-Side Request Forgery (SSRF) and deserialization attacks. This issue affects all versions prior to 2.0.0. The vulnerability can be exploited even if the isRemoteEnabled option is set to false. It allows attackers to perform SSRF, disclose internal image files, and cause PHAR deserialization attacks.

Weakness: CWE-611 (Improper Restriction of XML External Entity Reference)

## Which versions are affected by CVE-2021-3902?

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-2021-3902?

Upgrade dompdf/dompdf to 2.0.0 or later.

## Is CVE-2021-3902 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2021-3902 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-2021-3838](https://insights.sbomify.com/CVE-2021-3838/): PHAR Deserialization 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-2021-3902 and fix it if it is affected.

What it is: CVE-2021-3902 is a critical 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-2021-3902 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-2021-3902/ (Markdown: https://insights.sbomify.com/CVE-2021-3902/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-3902
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-3902
- OSV: https://osv.dev/vulnerability/CVE-2021-3902

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-3902/
Summaries are generated and may contain mistakes; the official description above is the record.