CVE-2026-63182

Received Received - Intake

Authentication Bypass in LightSAML via SAML Signature Spoofing

Publication date: 2026-10-30

Last updated on: 2026-10-30

Assigner: GitHub, Inc.

Description

LightSAML implements SAML 2.0 data model classes, XML serialization and deserialization, XML security, certificate support, and message bindings. Prior to 4.7.1 and 5.0.1, LightSAML and xmlseclibs disagree about which assertion an inbound SAML signature covers. `Response::deserialize` uses `manyElementsFromXml` to collect only direct-child `saml:Assertion` elements of `samlp:Response`, and `AssertionSignatureValidatorAction` validates their `ds:Signature` using an out-of-band trusted IdP credential resolved by Issuer, not a key from the document. `XMLSecurityDSig::validateReference()` removes the enveloped signature from the shared DOM, but `processRefNode()` resolves `Reference URI="#id"` document-wide through an XPath of the form `//*[@Id]` and takes `item(0)`, which need not be the assertion whose claims LightSAML consumes. An attacker who has captured one genuinely signed assertion, such as an earlier login response, can place its signature-stripped bytes earlier in `samlp:Extensions` and present a forged direct-child assertion with the same ID and copied genuine signature. Validation then covers the hidden genuine bytes while LightSAML surfaces unsigned attacker-controlled `Subject/NameID`, `Conditions`, and `Attributes`, enabling authentication bypass or privilege escalation even when signature validation is required. The behavior was confirmed in versions 5.0.0 and 4.6.1. This issue is fixed in versions 4.7.1 and 5.0.1.

CVSS Scores

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Meta Information

Published

2026-10-30

Last Modified

2026-10-30

Generated

2026-10-31

AI Q&A

2026-10-31

EPSS Evaluated

N/A

NVD

CVE-2026-63182

Affected Vendors & Products

Vendor	Product	Version / Range
litesaml	lightsaml	< 4.7.1
litesaml	lightsaml	>= 5.0.0, < 5.0.1

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-347	The product does not verify, or incorrectly verifies, the cryptographic signature for data.

Attack-Flow Graph

Executive Summary

LightSAML versions before 4.7.1 and 5.0.1 have a flaw in how they validate SAML signatures. The system incorrectly checks signatures against the wrong assertion in a SAML response, allowing an attacker to bypass authentication by injecting a forged assertion with a copied valid signature from a previous session.

Detection Guidance

Detecting this vulnerability requires checking the installed version of LightSAML. Use commands like 'composer show lightsaml/lightsaml' for PHP-based systems or inspect package managers for the version. Compare the output against versions 4.7.1, 5.0.1, or later to determine exposure.

Impact Analysis

This vulnerability could allow an attacker to impersonate a legitimate user, gain unauthorized access to systems, or escalate privileges. It undermines the security of SAML-based authentication, potentially leading to data breaches or unauthorized actions within affected applications.

Mitigation Strategies

Upgrade LightSAML to versions 4.7.1 or 5.0.1 immediately. If upgrading is not possible, review SAML responses for unexpected assertions in samlp:Extensions and validate all assertions strictly using in-document keys rather than out-of-band trusted IdP credentials.

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