CVE-2021-21239

MEDIUM LAB

PySAML2 <6.5.0 - Improper Signature Verification

Title source: llm
STIX 2.1

Exploitation Summary

EIP tracks 4 public exploits for CVE-2021-21239. PoCs published by Crims-on, illera88, GrantBirki.

AI-analyzed exploit summary This repository contains a functional PoC for CVE-2021-21239, an XML signature validation bypass vulnerability in xmlsec. The script manipulates XML input to exploit the flaw and signs it using a provided RSA key.

Description

PySAML2 is a pure python implementation of SAML Version 2 Standard. PySAML2 before 6.5.0 has an improper verification of cryptographic signature vulnerability. Users of pysaml2 that use the default CryptoBackendXmlSec1 backend and need to verify signed SAML documents are impacted. PySAML2 does not ensure that a signed SAML document is correctly signed. The default CryptoBackendXmlSec1 backend is using the xmlsec1 binary to verify the signature of signed SAML documents, but by default xmlsec1 accepts any type of key found within the given document. xmlsec1 needs to be configured explicitly to only use only _x509 certificates_ for the verification process of the SAML document signature. This is fixed in PySAML2 6.5.0.

Exploits (4)

nomisec WORKING POC
by Crims-on · poc
https://github.com/Crims-on/CVE-2021-21239

This repository contains a functional PoC for CVE-2021-21239, an XML signature validation bypass vulnerability in xmlsec. The script manipulates XML input to exploit the flaw and signs it using a provided RSA key.

Classification
Working Poc 90%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: xmlsec 1.2.25
No auth needed
Prerequisites: xmlsec installed · RSA private key
devstral-2 · analyzed Feb 27, 2026 Full analysis →
nomisec WORKING POC
by illera88 · poc
https://github.com/illera88/CVE-2021-21239

The repository contains a functional exploit for CVE-2021-21239, a SAML signature validation bypass in Redash <=10.1.0. The exploit forges a SAML response with an embedded public key to impersonate users and escalate privileges via JIT provisioning.

Classification
Working Poc 95%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: Redash <=10.1.0 (using pysaml2 <6.5.0)
No auth needed
Prerequisites: Access to Redash SAML callback endpoint · RSA key pair generation · Valid SAML template
devstral-2 · analyzed Feb 18, 2026 Full analysis →
nomisec WORKING POC
by GrantBirki · poc
https://github.com/GrantBirki/redash-vulnerable

This repository contains a functional exploit for CVE-2021-21239, an authentication bypass vulnerability in Redash due to improper SAML signature validation in pysaml2. The PoC includes a Dockerized vulnerable Redash instance and a Python script to forge SAML responses with embedded RSA keys.

Classification
Working Poc 95%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: Redash (using pysaml2 <= 6.4.1)
No auth needed
Prerequisites: Docker environment · Python 3.x · cryptography library · lxml library
devstral-2 · analyzed Feb 18, 2026 Full analysis →
nomisec WORKING POC
by RyanBoomer30 · poc
https://github.com/RyanBoomer30/CVE-2021-21239-Exploit

This repository contains a functional exploit for CVE-2021-21239, which manipulates SAML assertions by replacing attribute values and signature blocks to bypass authentication. The script automates the process of generating a malicious SAML response file.

Classification
Working Poc 90%
Attack Type
Auth Bypass
Complexity
Moderate
Reliability
Reliable
Target: VMware vRealize Operations Manager (vROps) 8.x
No auth needed
Prerequisites: Intercepted SAML XML file · OpenSSL and xmlsec1 installed
devstral-2 · analyzed Feb 18, 2026 Full analysis →

References (6)

Core 6
Core References
Product, Third Party Advisory x_refsource_misc
https://pypi.org/project/pysaml2
Exploit, Mailing List, Third Party Advisory x_refsource_misc
https://www.aleksey.com/pipermail/xmlsec/2013/009717.html
Mailing List, Third Party Advisory mailing-list x_refsource_mlist
https://lists.debian.org/debian-lts-announce/2021/02/msg00038.html

Scores

CVSS v3 6.5
EPSS 0.0068
EPSS Percentile 72.2%
Attack Vector NETWORK
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N

Details

CWE
CWE-347
Status published
Products (3)
debian/debian_linux 9.0
pypi/pysaml2 0 - 6.5.0PyPI
pysaml2_project/pysaml2 < 6.5.0
Published Jan 21, 2021
Tracked Since Feb 18, 2026