LightSAML up to 4.7.0/5.0.0 Signature Validation validateReference improper authentication

Summaryinfo

A vulnerability was found in LightSAML up to 4.7.0/5.0.0. It has been classified as critical. This impacts the function XMLSecurityDSig::validateReference of the component Signature Validation. This manipulation causes improper authentication. This vulnerability is tracked as CVE-2026-63182. The attack is possible to be carried out remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability classified as critical was found in LightSAML up to 4.7.0/5.0.0. Affected by this vulnerability is the function XMLSecurityDSig::validateReference of the component Signature Validation. The manipulation with an unknown input leads to a improper authentication vulnerability. The CWE definition for the vulnerability is CWE-287. When an actor claims to have a given identity, the product does not prove or insufficiently proves that the claim is correct. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

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.

It is possible to read the advisory at github.com. This vulnerability is known as CVE-2026-63182 since 07/16/2026. The exploitation appears to be easy. The attack can be launched remotely. Technical details of the vulnerability are known, but there is no available exploit.

Upgrading to version 4.7.1 or 5.0.1 eliminates this vulnerability.

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Productinfo

Name

• LightSAML

Version

• 4.0
• 4.1
• 4.2
• 4.3
• 4.4
• 4.5
• 4.6
• 4.7.0
• 5.0

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