How severe is CVE-2021-3902?

CVE-2021-3902 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3902?

CVE-2021-3902 affects the following packages: dompdf/dompdf (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-3902?

Update dompdf/dompdf to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3902 is resolved across your whole dependency graph.

How do I detect CVE-2021-3902 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompdf/dompdf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.

How do I mitigate CVE-2021-3902 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2021-3902?

O3 pinpoints whether CVE-2021-3902 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Is CVE-2021-3902 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-3902, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-3902?

CVE-2021-3902 has an EPSS (Exploit Prediction Scoring System) score of 0.9%, placing it in the 56th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

When was CVE-2021-3902 published, and has it been updated?

CVE-2021-3902 was published on November 15, 2024 and was last updated on April 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2021-3902: dompdf/dompdf Server-Side Request Forgery (Criti…

EPSS Exploitation Probability

via FIRST.org ↗

0.9%probability of exploitation in next 30 days

Lower Risk56th percentile-4.17%

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

Blast Radius

1 pkg affected

🐘dompdf/dompdf

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

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.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`dompdf/dompdf`	all versions	2.0.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for dompdf/dompdf. O3's reachability analysis confirms whether the vulnerable code path is actually invoked in your application, so you act on real exposure instead of every transitive match.
Fix
Update dompdf/dompdf to 2.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3902 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 pinpoints whether CVE-2021-3902 is reachable in your code and exactly where to fix it, then blocks exploitation in production at runtime until the patched version is deployed.

Tailored to CVE-2021-3902. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2021-3902 in your dependencies?

O3 detects CVE-2021-3902 across Packagist dependencies and uses function-level reachability to confirm whether the vulnerable code path is actually reachable — not just present. No false positives.

Scan my dependencies How O3 SCA works

CVE-2021-3902