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-2018-19990020x00 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 hudson/plugin/SHORTNAME.
**/
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>/** * 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.
*
*
* The syntax of the locale specific resource is the same as property file localization.
* So Japanese resource for foo.html would be named foo_ja.html.
*
* @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> if(idx=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
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