作者:[email protected]知道创宇404实验室
时间:2019年4月8日
看到官方发布了预警,于是开始了漏洞应急。漏洞描述中指出Confluence Server与Confluence Data Center中的Widget Connector存在服务端模板注入漏洞,***者能利用此漏洞能够实现目录穿越与远程代码执行。
确认漏洞点是Widget Connector,下载最新版的比对补丁,发现在com\atlassian\confluence\extra\widgetconnector\WidgetMacro.java里面多了一个过滤,这个应该就是这个漏洞最关键的地方。
可以看到
this.sanitizeFields = Collections.unmodifiableList(Arrays.asList(VelocityRenderService.TEMPLATE_PARAM));
而TEMPLATE_PARAM的值就是_template,所以这个补丁就是过滤了外部传入的_template参数。
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<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">interface</span> <span class="hljs-title">VelocityRenderService</span> </span>{ <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String WIDTH_PARAM = <span class="hljs-string">"width"</span>; <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String HEIGHT_PARAM = <span class="hljs-string">"height"</span>; <span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String TEMPLATE_PARAM = <span class="hljs-string">"_template"</span>; |
翻了一下Widget Connector里面的文件,发现TEMPLATE_PARAM就是模板文件的路径。
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<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">FriendFeedRenderer</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WidgetRenderer</span> </span>{ <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String MATCH_URL = <span class="hljs-string">"friendfeed.com"</span>; <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String PATTERN = <span class="hljs-string">"friendfeed.com/(\\w+)/?"</span>; <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> String VELOCITY_TEMPLATE = <span class="hljs-string">"com/atlassian/confluence/extra/widgetconnector/templates/simplejscript.vm"</span>; <span class="hljs-keyword">private</span> VelocityRenderService velocityRenderService; ...... <span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">getEmbeddedHtml</span><span class="hljs-params">(String url, Map<String, String> params)</span> </span>{ params.put(VelocityRenderService.TEMPLATE_PARAM, VELOCITY_TEMPLATE); <span class="hljs-keyword">return</span> velocityRenderService.render(getEmbedUrl(url), params); } |
加载外部的链接时,会调用相对的模板去渲染,如上,模板的路径一般是写死的,但是也有例外,补丁的作用也说明有人突破了限制,调用了意料之外的模板,从而造成了模板注入。
在了解了补丁和有了一些大概的猜测之后,开始尝试。
首先先找到这个功能,翻了一下官方的文档,找到了这个功能,可以在文档中嵌入一些视频,文档之类的。
看到这个,有点激动了,因为在翻补丁的过程中,发现了几个参数,url,width,height正好对应着这里,那_template是不是也从这里传递进去的?
随便找个Youtube视频插入试试,点击预览,抓包。
在params中尝试插入_template参数,好吧,没啥反应。。
开始debug模式,因为测试插入的是Youtube视频,所以调用的是com/atlassian/confluence/extra/widgetconnector/video/YoutubeRenderer.class
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<span class="hljs-keyword">public</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">YoutubeRenderer</span> <span class="hljs-keyword">implements</span> <span class="hljs-title">WidgetRenderer</span>, <span class="hljs-title">WidgetImagePlaceholder</span> </span>{ <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> Pattern YOUTUBE_URL_PATTERN = Pattern.compile(<span class="hljs-string">"https?://(.+\\.)?youtube.com.*(\\?v=([^&]+)).*$"</span>); <span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> PlaceholderService placeholderService; <span class="hljs-keyword">private</span> <span class="hljs-keyword">final</span> String DEFAULT_YOUTUBE_TEMPLATE = <span class="hljs-string">"com/atlassian/confluence/extra/widgetconnector/templates/youtube.vm"</span>; ...... <span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">getEmbedUrl</span><span class="hljs-params">(String url)</span> </span>{ Matcher youtubeUrlMatcher = YOUTUBE_URL_PATTERN.matcher(<span class="hljs-keyword">this</span>.verifyEmbeddedPlayerString(url)); <span class="hljs-keyword">return</span> youtubeUrlMatcher.matches() ? String.format(<span class="hljs-string">"//www.youtube.com/embed/%s?wmode=opaque"</span>, youtubeUrlMatcher.group(<span class="hljs-number">3</span>)) : <span class="hljs-keyword">null</span>; } <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">matches</span><span class="hljs-params">(String url)</span> </span>{ <span class="hljs-keyword">return</span> YOUTUBE_URL_PATTERN.matcher(<span class="hljs-keyword">this</span>.verifyEmbeddedPlayerString(url)).matches(); } <span class="hljs-function"><span class="hljs-keyword">private</span> String <span class="hljs-title">verifyEmbeddedPlayerString</span><span class="hljs-params">(String url)</span> </span>{ <span class="hljs-keyword">return</span> !url.contains(<span class="hljs-string">"feature=player_embedded&"</span>) ? url : url.replace(<span class="hljs-string">"feature=player_embedded&"</span>, <span class="hljs-string">""</span>); } <span class="hljs-function"><span class="hljs-keyword">public</span> String <span class="hljs-title">getEmbeddedHtml</span><span class="hljs-params">(String url, Map<String, String> params)</span> </span>{ <span class="hljs-keyword">return</span> <span class="hljs-keyword">this</span>.velocityRenderService.render(<span class="hljs-keyword">this</span>.getEmbedUrl(url), <span class="hljs-keyword">this</span>.setDefaultParam(params)); } |
在getEmbeddedHtml下断点,先会调用getEmbedUrl对用户传入的url进行正则匹配,因为我们传入的是个正常的Youtube视频,所以这里是没有问题的,然后调用setDefaultParam函数对传入的其他参数进行处理。
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<span class="hljs-function"><span class="hljs-keyword">private</span> Map<String, String> <span class="hljs-title">setDefaultParam</span>(<span class="hljs-params">Map<String, String> <span class="hljs-keyword">params</span></span>) </span>{ String width = (String)<span class="hljs-keyword">params</span>.<span class="hljs-keyword">get</span>(<span class="hljs-string">"width"</span>); String height = (String)<span class="hljs-keyword">params</span>.<span class="hljs-keyword">get</span>(<span class="hljs-string">"height"</span>); <span class="hljs-keyword">if</span> (!<span class="hljs-keyword">params</span>.containsKey(<span class="hljs-string">"_template"</span>)) { <span class="hljs-keyword">params</span>.put(<span class="hljs-string">"_template"</span>, <span class="hljs-string">"com/atlassian/confluence/extra/widgetconnector/templates/youtube.vm"</span>); } <span class="hljs-keyword">if</span> (StringUtils.isEmpty(width)) { <span class="hljs-keyword">params</span>.put(<span class="hljs-string">"width"</span>, <span class="hljs-string">"400px"</span>); } <span class="hljs-function"><span class="hljs-keyword">else</span> <span class="hljs-title">if</span> (<span class="hljs-params">StringUtils.isNumeric(width</span>)) </span>{ <span class="hljs-keyword">params</span>.put(<span class="hljs-string">"width"</span>, width.concat(<span class="hljs-string">"px"</span>)); } <span class="hljs-keyword">if</span> (StringUtils.isEmpty(height)) { <span class="hljs-keyword">params</span>.put(<span class="hljs-string">"height"</span>, <span class="hljs-string">"300px"</span>); } <span class="hljs-function"><span class="hljs-keyword">else</span> <span class="hljs-title">if</span> (<span class="hljs-params">StringUtils.isNumeric(height</span>)) </span>{ <span class="hljs-keyword">params</span>.put(<span class="hljs-string">"height"</span>, height.concat(<span class="hljs-string">"px"</span>)); } <span class="hljs-keyword">return</span> <span class="hljs-keyword">params</span>; } |
取出width和height来判断是否为空,为空则设置默认值。关键的_template参数来了,如果外部传入的参数没有_template,则设置默认的Youtube模板。如果传入了,就使用传入的,也就是说,aaaa是成功的传进来了。
大概翻了一下Widget Connector里面的Renderer,大部分是不能设置_template的,是直接写死了,也有一些例外,如Youtube,Viddler,DailyMotion等,是可以从外部传入_template的。
能传递_template了,接下来看下是如何取模板和渲染模板的。
跟进this.velocityRenderService.render,也就是com/atlassian/confluence/extra/widgetconnector/services/DefaultVelocityRenderService.class里面的render方法。
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public <span class="hljs-built_in">String</span> render(<span class="hljs-built_in">String</span> url, <span class="hljs-built_in">Map</span><<span class="hljs-built_in">String</span>, <span class="hljs-built_in">String</span>> params) { <span class="hljs-built_in">String</span> width = (<span class="hljs-built_in">String</span>)params.get(<span class="hljs-string">"width"</span>); <span class="hljs-built_in">String</span> height = (<span class="hljs-built_in">String</span>)params.get(<span class="hljs-string">"height"</span>); <span class="hljs-built_in">String</span> template = (<span class="hljs-built_in">String</span>)params.get(<span class="hljs-string">"_template"</span>); <span class="hljs-keyword">if</span> (StringUtils.isEmpty(template)) { template = <span class="hljs-string">"com/atlassian/confluence/extra/widgetconnector/templates/embed.vm"</span>; } <span class="hljs-keyword">if</span> (StringUtils.isEmpty(url)) { <span class="hljs-keyword">return</span> <span class="hljs-literal">null</span>; } <span class="hljs-keyword">else</span> { <span class="hljs-built_in">Map</span><<span class="hljs-built_in">String</span>, <span class="hljs-built_in">Object</span>> contextMap = <span class="hljs-keyword">this</span>.getDefaultVelocityContext(); Iterator var7 = params.entrySet().iterator(); <span class="hljs-keyword">while</span>(var7.hasNext()) { Entry<<span class="hljs-built_in">String</span>, <span class="hljs-built_in">String</span>> entry = (Entry)var7.next(); <span class="hljs-keyword">if</span> (((<span class="hljs-built_in">String</span>)entry.getKey()).contentEquals(<span class="hljs-string">"tweetHtml"</span>)) { contextMap.put(entry.getKey(), entry.getValue()); } <span class="hljs-keyword">else</span> { contextMap.put(entry.getKey(), GeneralUtil.htmlEncode((<span class="hljs-built_in">String</span>)entry.getValue())); } } contextMap.put(<span class="hljs-string">"urlHtml"</span>, GeneralUtil.htmlEncode(url)); <span class="hljs-keyword">if</span> (StringUtils.isNotEmpty(width)) { contextMap.put(<span class="hljs-string">"width"</span>, GeneralUtil.htmlEncode(width)); } <span class="hljs-keyword">else</span> { contextMap.put(<span class="hljs-string">"width"</span>, <span class="hljs-string">"400"</span>); } <span class="hljs-keyword">if</span> (StringUtils.isNotEmpty(height)) { contextMap.put(<span class="hljs-string">"height"</span>, GeneralUtil.htmlEncode(height)); } <span class="hljs-keyword">else</span> { contextMap.put(<span class="hljs-string">"height"</span>, <span class="hljs-string">"300"</span>); } <span class="hljs-keyword">return</span> <span class="hljs-keyword">this</span>.getRenderedTemplate(template, contextMap); } } |
_template取出来赋值给template,其他传递进来的参数取出来经过判断之后放入到contextMap,调用getRenderedTemplate函数,也就是调用VelocityUtils.getRenderedTemplate。
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protected <span class="hljs-built_in">String</span> getRenderedTemplate(<span class="hljs-built_in">String</span> template, <span class="hljs-built_in">Map</span><<span class="hljs-built_in">String</span>, <span class="hljs-built_in">Object</span>> contextMap){ <span class="hljs-keyword">return</span> VelocityUtils.getRenderedTemplate(template, contextMap); } |
一路调用,调用链如下图,最后来到/com/atlassian/confluence/util/velocity/ConfigurableResourceManager.class的loadResource函数,来获取模板。
这里调用了4个ResourceLoader去取模板。
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<span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.atlassian</span><span class="hljs-selector-class">.confluence</span><span class="hljs-selector-class">.setup</span><span class="hljs-selector-class">.velocity</span><span class="hljs-selector-class">.HibernateResourceLoader</span> <span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.velocity</span><span class="hljs-selector-class">.runtime</span><span class="hljs-selector-class">.resource</span><span class="hljs-selector-class">.loader</span><span class="hljs-selector-class">.FileResourceLoader</span> <span class="hljs-selector-tag">org</span><span class="hljs-selector-class">.apache</span><span class="hljs-selector-class">.velocity</span><span class="hljs-selector-class">.runtime</span><span class="hljs-selector-class">.resource</span><span class="hljs-selector-class">.loader</span><span class="hljs-selector-class">.ClasspathResourceLoader</span> <span class="hljs-selector-tag">com</span><span class="hljs-selector-class">.atlassian</span><span class="hljs-selector-class">.confluence</span><span class="hljs-selector-class">.setup</span><span class="hljs-selector-class">.velocity</span><span class="hljs-selector-class">.DynamicPluginResourceLoader</span> |
这里主要看下Velocity自带的FileResourceLoader和ClasspathResourceLoader
FileResourceLoader会对用户传入的模板路径使用normalizePath函数进行校验
可以看到,过滤了/../,这样就导致没有办法跳目录了。
路径过滤后调用findTemplate查找模板,可看到,会拼接一个固定的path,这是Confluence的安装路径。
也就是说现在可以利用FileResourceLoader来读取Confluence目录下面的文件了。
尝试读取/WEB-INF/web.xml文件,可以看到,是成功的加载到了该文件。
但是这个无法跳出Confluence的目录,因为不能用/../。
再来看下ClasspathResourceLoader
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<span class="hljs-function"><span class="hljs-keyword">public</span> InputStream <span class="hljs-title">getResourceStream</span><span class="hljs-params">(String name)</span> <span class="hljs-keyword">throws</span> ResourceNotFoundException </span>{ InputStream result = <span class="hljs-keyword">null</span>; <span class="hljs-keyword">if</span> (StringUtils.isEmpty(name)) { <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> ResourceNotFoundException(<span class="hljs-string">"No template name provided"</span>); } <span class="hljs-keyword">else</span> { <span class="hljs-keyword">try</span> { result = ClassUtils.getResourceAsStream(<span class="hljs-keyword">this</span>.getClass(), name); ...... } |
跟进ClassUtils.getResourceAsStream
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<span class="hljs-keyword">public</span> <span class="hljs-keyword">static</span> InputStream getResourceAsStream(<span class="hljs-class"><span class="hljs-keyword">Class</span> <span class="hljs-title">claz</span>, <span class="hljs-title">String</span> <span class="hljs-title">name</span>) </span>{ <span class="hljs-keyword">while</span>(name.startsWith(<span class="hljs-string">"/"</span>)) { name = name.substring(<span class="hljs-number">1</span>); } ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); InputStream result; <span class="hljs-keyword">if</span> (classLoader == <span class="hljs-keyword">null</span>) { classLoader = claz.getClassLoader(); result = classLoader.getResourceAsStream(name); } <span class="hljs-keyword">else</span> { result = classLoader.getResourceAsStream(name); <span class="hljs-keyword">if</span> (result == <span class="hljs-keyword">null</span>) { classLoader = claz.getClassLoader(); <span class="hljs-keyword">if</span> (classLoader != <span class="hljs-keyword">null</span>) { result = classLoader.getResourceAsStream(name); } } } <span class="hljs-keyword">return</span> result; } |
会跳到/org/apache/catalina/loader/WebappClassLoaderBase.class
跟进,发现会拼接/WEB-INF/classes,而且其中也是调用了normalize对传入的路径进行过滤。。
这里还是可以用../跳一级目录。
尝试读取一下../web.xml,可以看到,也是可以读取成功的,但是仍然无法跳出目录。
我这里测试用的版本是6.14.1,而后尝试了file://,http://,https:// 都没有成功。后来我尝试把Cookie删掉,发现还是可以读取文件,确认了这个漏洞不需要权限,但是跳不出目录。应急就在这里卡住了。
而后的几天,有大佬说用file:// 协议可以跳出目录限制,我惊了,我确定当时是已经试过了,没有成功的。看了大佬的截图,发现用的是6.9.0的版本,我下载了,尝试了一下,发现真的可以。
问题还是在ClasspathResourceLoader上面,步骤和之前的是一样的,断到/org/apache/catalina/loader/WebappClassLoaderBase.class的getResourceAsStream方法
前面拼接/WEB-INF/classes获取失败后,继续往下进行。
跟进findResource,函数前面仍然获取失败
关键的地方就在这里,会调用super.findResource(name),这里返回了URL,也就是能获取到对象。
不仅如此,这里还可以使用其他协议(https,ftp等)获取远程的对象,意味着可以加载远程的对象。
获取到URL对象之后,继续回到之前的getResourceAsStream,可以看到,当返回的url不为null时,
会调用url.openStream()获取数据。
最终获取到数据给Velocity渲染。
尝试一下
至于6.14.1为啥不行,赶着应急,后续会跟,如果有新的发现,会同步上来,目前只看到ClassLoader不一样。
6.14.1
6.9.0
这两个loader的关系如下
现在可以加载本地和远程模板了,可以尝试进行RCE。
关于Velocity的RCE,基本上payload都来源于15年blackhat的服务端模板注入的议题,但是在Confluence上用不了,因为在调用方法的时候会经过velocity-htmlsafe-1.5.1.jar,里面多了一些过滤和限制。但是仍然可以利用反射来执行命令。
用python -m pyftpdlib -p 2121开启一个简单的ftp服务器,将payload保存成rce.vm,保存在当前目录。
将_template设置成ftp://localhost:2121/rce.vm, 发送,成功执行命令。
对于命令回显,同样可以使用反射构造出payload,执行ipconfig的结果。
漏洞影响
根据 ZoomEye 网络空间搜索引擎对关键字 “X-Confluence” 进行搜索,共得到 61,856 条结果,主要分布美国、德国、中国等国家。
全球分布(非漏洞影响范围)
中国分布(非漏洞影响范围)
漏洞检测
2019年4月4日,404实验室公布了该漏洞的检测PoC,可以利用这个PoC检测Confluence是否受该漏洞影响。
参 考 链 接
[2] Remote code execution via Widget Connector macro – CVE-2019-3396
[3] 漏洞预警 | Confluence Server 远程代码执行漏洞
拓展阅读(点评/知识):
Confluence安装
https://www.cnblogs.com/vcdx/p/9490606.html
安装包下载
链接: https://pan.baidu.com/s/1zfkTubVFXcPOZP2dHMIQrg 密码: vhn3
本文标题: | Confluence 未授权 RCE (CVE-2019-3396) 漏洞分析 |
本文链接: (转载请附上本文链接) | http://vulsee.com/archives/vulsee_2019/0412_7433.html |