CVE-2021-39171Network attack vector

Unauthenticated denial of service via unlimited XML transforms

Published Aug 27, 2021 · Updated Aug 4, 2024

Denial of service in Passport-SAML before 3.1.0 allows remote attackers to consume significant resources via malicious SAML transforms. During signed-node processing, the library accepts an unbounded number of XML transforms, causing excessive CPU work on attacker-supplied SAML payloads. No authentication or user interaction is required; repeated network requests can reduce or deny service availability without data disclosure or modification.

CVSS severity5.3
Medium
EPSS probability1.32%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Denial of service in Passport-SAML before 3.1.0 allows remote attackers to consume significant resources via malicious SAML transforms. During signed-node processing, the library accepts an unbounded number of XML transforms, causing excessive CPU work on attacker-supplied SAML payloads. No authentication or user interaction is required; repeated network requests can reduce or deny service availability without data disclosure or modification.

The record

CVE
CVE-2021-39171
Published
Aug 27, 2021
Updated
Aug 4, 2024
Vendor
node-saml
Product
Passport-SAML
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 27, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=< 3.1.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

node-saml · Passport-SAMLversion=< 3.1.0

Published CVSS scores

7.5NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
5.3GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L
5.0NVDAV:N/AC:L/Au:N/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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