jenkins任意文件读取漏洞复现与分析 -CVE-2018-1999002

jenkins任意文件读取漏洞复现与分析 -CVE-2018-1999002

0x00 漏洞影响版本

Jenkins weekly up to and including 2.132
Jenkins LTS up to and including 2.121.1

0x01 漏洞原理分析

在没有登陆（未授权，cookie清空）的情况下，只有当管理员开启了allow anonymous read access的时候，才能实现任意文件读取，否则仍需登陆。



以payload为例，请求的url为/plugin/credentials/.ini。而在hudson/Plugin.java:227

/**
* This method serves static resources in the plugin under <tt>hudson/plugin/SHORTNAME</tt>.
**/
public void doDynamic(StaplerRequest req, StaplerResponse rsp) throws IOException, ServletException {
String path = req.getRestOfPath();

String pathUC = path.toUpperCase(Locale.ENGLISH);
if (path.isEmpty() || path.contains("..") || path.startsWith(".") || path.contains("%") || pathUC.contains("META-INF") || pathUC.contains("WEB-INF")) {
LOGGER.warning("rejecting possibly malicious " + req.getRequestURIWithQueryString());
rsp.sendError(HttpServletResponse.SC_BAD_REQUEST);
return;
}

// Stapler routes requests like the "/static/.../foo/bar/zot" to be treated like "/foo/bar/zot"
// and this is used to serve long expiration header, by using Jenkins.VERSION_HASH as "..."
// to create unique URLs. Recognize that and set a long expiration header.
String requestPath = req.getRequestURI().substring(req.getContextPath().length());
boolean staticLink = requestPath.startsWith("/static/");

long expires = staticLink ? TimeUnit2.DAYS.toMillis(365) : -1;

// use serveLocalizedFile to support automatic locale selection

rsp.serveLocalizedFile(req, new URL(wrapper.baseResourceURL, '.' + path), expires);
}

doDynamic函数用于处理类似/plugin/xx的请求，serveLocalizedFile在stapler-1.250-sources.jar!/org/kohsuke/stapler/ResponseImpl.java第209行左右：

public void serveLocalizedFile(StaplerRequest request, URL res, long expiration) throws ServletException, IOException {
if(!stapler.serveStaticResource(request, this, stapler.selectResourceByLocale(res,request.getLocale()), expiration))
sendError(SC_NOT_FOUND);
}

先看最里面的request.getLocale()，然后再来分析stapler.selectResourceByLocale()。
跟入request.getLocale()，至jetty-server-9.2.15.v20160210-sources.jar!/org/eclipse/jetty/server/Request.java:692:

@Override
public Locale getLocale()
{
...

if (size > 0)
{
String language = (String)acceptLanguage.get(0);
language = HttpFields.valueParameters(language,null);
String country = "";
int dash = language.indexOf('-');
if (dash > -1)
{
country = language.substring(dash + 1).trim();
language = language.substring(0,dash).trim();
}
return new Locale(language,country);
}

return Locale.getDefault();
}

这里用于处理HTTP请求中的Accept-Language头部。比如zh-cn，则会根据-的位置被分为两部分，language为zh，country为cn，然后返回Locale(language,country)对象。倘若不存在-，则country为空，language即对应我们的payload:../../../../../../../../../../../../windows/win，则此时返回一个Locale(language,"")

返回后即进入selectResourceByLocale(URL url, Locale locale),这里的locale参数即上一步返回的locale对象。

OpenConnection selectResourceByLocale(URL url, Locale locale) throws IOException {
// hopefully HotSpot would be able to inline all the virtual calls in here
return urlLocaleSelector.open(url.toString(),locale,url);
}

urlLocaleSelector对象的声明见stapler-1.250-sources.jar!/org/kohsuke/stapler/Stapler.java:390:

private final LocaleDrivenResourceSelector urlLocaleSelector = new LocaleDrivenResourceSelector() {
@Override
URL map(String url) throws IOException {
return new URL(url);
}
};

在stapler-1.250-sources.jar!/org/kohsuke/stapler/Stapler.java:324实现了LocaleDrivenResourceSelector类的open方法：

private abstract class LocaleDrivenResourceSelector {
/**
* The 'path' is divided into the base part and the extension, and the locale-specific
* suffix is inserted to the base portion. {@link #map(String)} is used to convert
* the combined path into {@link URL}, until we find one that works.
*
* <p>
* The syntax of the locale specific resource is the same as property file localization.
* So Japanese resource for <tt>foo.html</tt> would be named <tt>foo_ja.html</tt>.
*
* @param path
*      path/URL-like string that represents the path of the base resource,
*      say "foo/bar/index.html" or "file:///a/b/c/d/efg.png"
* @param locale
*      The preferred locale
* @param fallback
*      The {@link URL} representation of the {@code path} parameter
*      Used as a fallback.
*/
OpenConnection open(String path, Locale locale, URL fallback) throws IOException {
String s = path;
int idx = s.lastIndexOf('.');
if(idx<0)   // no file extension, so no locale switch available
return openURL(fallback);
String base = s.substring(0,idx);
String ext = s.substring(idx);
if(ext.indexOf('/')>=0) // the '.' we found was not an extension separator
return openURL(fallback);

OpenConnection con;

// try locale specific resources first.
con = openURL(map(base + '_' + locale.getLanguage() + '_' + locale.getCountry() + '_' + locale.getVariant() + ext));
if(con!=null)   return con;
con = openURL(map(base+'_'+ locale.getLanguage()+'_'+ locale.getCountry()+ext));
if(con!=null)   return con;
con = openURL(map(base+'_'+ locale.getLanguage()+ext));
if(con!=null)   return con;
// default
return openURL(fallback);
}

/**
* Maps the 'path' into {@link URL}.
*/
abstract URL map(String path) throws IOException;
}

先看看开头的注释，这段代码本意是想根据对应的语言（Accept-Language）来返回不同的文件，比如在ja的条件下请求foo.html，则相当于去请求foo_ja.html，这个过程会先把foo.html分成两部分：文件名foo和扩展名.html，然后根据具体的语言/国家来组合成最终的文件名。

结合payload来看，我们请求的url为/plugin/credentials/.ini，则base为空，扩展名（ext变量）即为.ini，然后通过一系列的尝试openURL，在此例中即最后一个情形con = openURL(map(base+''+ locale.getLanguage()+ext));，会去请求../../../../../../../../../../../../windows/win.ini ，尽管目录_..并不存在，但在win下可以直接通过路径穿越来绕过。但在linux，则需要一个带有_的目录来想办法绕过。

0x02 限制

对windows系统： 没有限制
对linux系统： 目录中需要存在 '_'

参考链接：https://xz.aliyun.com/t/2486