CVE-2021-27736Network attack vector

File disclosure and SSRF via external entities

Published Apr 22, 2021 · Updated Aug 3, 2024

XXE in FusionAuth fusionauth-samlv2 before 0.5.4 allows remote attackers to read local files or send server-side network requests. The parseFromBytes function creates a DocumentBuilderFactory without disabling document type definitions, so forged AuthnRequest or LogoutRequest XML resolves external entities. An exposed SAML endpoint accepts these messages without a signature and reflects resolved entity content on an error page.

CVSS severity6.5
Medium
EPSS probability1.28%
Next 30 days · Sep 17, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

XXE in FusionAuth fusionauth-samlv2 before 0.5.4 allows remote attackers to read local files or send server-side network requests. The parseFromBytes function creates a DocumentBuilderFactory without disabling document type definitions, so forged AuthnRequest or LogoutRequest XML resolves external entities. An exposed SAML endpoint accepts these messages without a signature and reflects resolved entity content on an error page.

The record

CVE
CVE-2021-27736
Published
Apr 22, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-611, T1190, T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 22, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:P/I:N/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

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-611Improper Restriction of XML External Entity Reference
T1190Exploit Public-Facing Application
T1005Data from Local System

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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