How severe is CVE-2021-39171?

CVE-2021-39171 has a CVSS score of 7.5/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-39171?

CVE-2021-39171 affects the following packages: passport-saml (npm). Ecosystems affected: npm.

How do I fix CVE-2021-39171?

Update passport-saml to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39171 is resolved across your whole dependency graph.

How do I detect CVE-2021-39171 in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for passport-saml. 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-2021-39171 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-2021-39171?

O3 pinpoints whether CVE-2021-39171 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-2021-39171 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-39171 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-39171?

CVE-2021-39171 has an EPSS (Exploit Prediction Scoring System) score of 1.3%, placing it in the 67th 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.

What type of vulnerability is CVE-2021-39171?

CVE-2021-39171 is classified as Uncontrolled Resource Consumption (CWE-400). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-39171 published, and has it been updated?

CVE-2021-39171 was published on August 27, 2021 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-2021-39171: Unlimited transforms allowed for signed nodes…

EPSS Exploitation Probability

via FIRST.org ↗

1.3%probability of exploitation in next 30 days

Lower Risk67th percentile+0.86%

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

Weekly download volume for affected packages — a proxy for how broadly this vulnerability is deployed.

passport-samlnpm

145Kdownloads / week

Description

Passport-SAML is a SAML 2.0 authentication provider for Passport, the Node.js authentication library. Prior to version 3.1.0, a malicious SAML payload can require transforms that consume significant system resources to process, thereby resulting in reduced or denied service. This would be an effective way to perform a denial-of-service attack. This has been resolved in version 3.1.0. The resolution is to limit the number of allowable transforms to 2.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`passport-saml`	all versions	3.1.0

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for passport-saml. 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 passport-saml to 3.1.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-39171 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-2021-39171 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-2021-39171. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

Passport-SAML is a SAML 2.0 authentication provider for Passport, the Node.js authentication library. Prior to version 3.1.0, a malicious SAML payload can require transforms that consume significant system resources to process, thereby resulting in reduced or denied service. This would be an effective way to perform a denial-of-service attack. This has been resolved in version 3.1.0. The resolution is to limit the number of allowable transforms to 2.

O3 Security · Impact-Aware SCA

Is CVE-2021-39171 in your dependencies?

O3 detects CVE-2021-39171 across npm 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-2021-39171