CVE-2026-49289
Received Received - Intake

XPath DoS in SimpleSAMLphp SAML2 Library

Publication date: 2026-08-19

Last updated on: 2026-08-19

Assigner: GitHub, Inc.

Description
The SimpleSAMLphp SAML2 library is a PHP library for SAML2 related functionality. In 4.19.2 and 4.20.2, the library permits attacker-controlled XPath transforms while processing XML signatures in specially crafted SAML messages. XPath evaluation can consume uncontrolled processing resources, allowing a remote unauthenticated attacker to deny service to any entity relying on SimpleSAMLphp or directly on the SAML2 library. The mitigation limits the number of transforms, permits only transform algorithms identified by the SAML 2.0 Core specification, and specifically rejects XPath transforms. This issue is fixed in versions 4.19.3 and 4.20.3.

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Meta Information

Published
2026-08-19
Last Modified
2026-08-19
Generated
2026-08-19
AI Q&A
2026-08-19
EPSS Evaluated
N/A
NVD
CVE-2026-49289
EUVD
EUVD-2026-62505

Affected Vendors & Products

Showing 6 associated CPEs
Vendor Product Version / Range
simplesamlphp saml2 4.19.2
simplesamlphp saml2 4.20.2
simplesamlphp saml2 to 4.19.3 (inc)
simplesamlphp saml2 to 4.20.3 (inc)
simplesamlphp saml2 From 4.20.2 (exc)
simplesamlphp saml2 From 4.19.2 (exc)

Helpful Resources

Exploitability

CWE
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KEV
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CWE ID Description
CWE-400 The product does not properly control the allocation and maintenance of a limited resource.

Attack-Flow Graph

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Executive Summary

This vulnerability is a Denial of Service (DoS) issue in the SimpleSAMLphp SAML2 library. It allows attackers to send specially crafted SAML messages with uncontrolled XPath transforms, consuming excessive processing resources. The library permits these transforms in versions 4.19.2 and 4.20.2, leading to system slowdowns or crashes. The issue is fixed in versions 4.19.3 and 4.20.3.

Detection Guidance

To detect this vulnerability, inspect SAML messages for excessive XPath transforms or unsupported transform algorithms in ds:Reference elements. Check logs for failed signature validations or exceptions related to transform limits. Use tools like Wireshark to analyze SAML traffic for malformed assertions.

Impact Analysis

If you use SimpleSAMLphp or the SAML2 library in versions 4.19.2 or 4.20.2, an attacker could exploit this to cause a DoS. This means your systems may become unresponsive or crash, disrupting services for users relying on SAML authentication. The impact is remote and does not require authentication.

Compliance Impact

This vulnerability primarily causes Denial of Service (DoS) conditions by consuming excessive processing resources through XPath transforms in SAML messages. While it does not directly expose or leak data, it can disrupt services relying on SimpleSAMLphp or the SAML2 library, potentially impacting availability of systems handling sensitive data.

Mitigation Strategies

Upgrade to patched versions 4.19.3 or 4.20.3 of the simplesamlphp/saml2 library. Apply input validation to reject SAML messages with more than two transforms or prohibited algorithms. Monitor for DoS attempts and block malicious IPs.

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