Jenkins Groovy scripts for red teamers and penetration testers

Hello folks! It is has been a while since we posted in this blog. After the summer relaxation we are ready to come back! Let’s start with this whitepaper on Jenkins Groovy scripting.

OAMBuster – Multithreaded exploit for CVE-2018-2879

Oracle OAM is a widely used component that handles authentication for many web applications. Any request to a protected resource on the web application redirects to OAM, acting as middleware to perform user authentication.

Last year, a vulnerability was found in the login process which contains a serious cryptographic flaw. It can be exploited to:

  • Steal a session token
  • Create a session token for any user

Basically it allows to login to the website and impersonate any user. Bad stuff.

Technical Details

During login, Oracle OAM will send a value called encquery as part of the URL. This parameter contains some values like a salt and a timestamp, and is encrypted with AES-CBC. However:

  • There is no HMAC attached, to verify that the encrypted string wasn’t tampered with
  • The website responds with an error message when there is a padding error during decryption

This makes it vulnerable to a classic Padding Oracle Attack.

With AES-CBC, blocks of ciphertext are chained and dependent on each other. By adding blocks at the end and tampering with the second-to-last block, we can learn if the plain text is valid.

However, there is one extra challenge: We can not just add blocks of data to the end of the string because the decrypted value contains a validation hash at the end. When adding a block (that turns into gibberish when decrypted), the hash won’t be valid and we will not be able to use the oracle – it simply will always provide an error.

The fix to this problem is simple: we first have to search for the character that turns into a space (0x20) when decrypted. Now the hash will be untouched, and the gibberish we place behind it is interpreted as a new value.

For more in depth information, please read these excellent blog posts by SEC Consult:

Exploit

There have been exploits in the wild for some time, but they are single threaded. Because this attack requires to guess byte values one by one, it can take about 4 hours to complete (without rate limiting).

With RedTimmy, we have developed a multithreaded version of the exploit called OAMBuster. Source code is available on GitHub.

The first two stages of the attack, showing the verification of a target being vulnerable to CVE-2018-2879.

OAMBuster is able to perform the following actions:

  • Verify if the target is vulnerable to the attack (<30 seconds)
  • Decrypt the encquery string, using POA
  • Decrypt any given string, using POA
  • Encrypt any given string, using POA

The final two functions can be used for example to decrypt the OAMAuthnCookie containing the session token, and then re-encrypt it.

Benefits of the multithreaded implementation

Because OAMBuster has multiple threads running, it can decrypt multiple blocks at the same time. So for example, when there are 16 blocks in total, the tool can run 16 threads on the last byte of each block. When a thread is finished, it continues to work on the second-to-last byte of the block, and so forth, working from back to front. Bytes within a block can not be parallelized, as they are dependent on each other.

Worthless to say, you can subscribe our blackhat course if you want to play with it more:

Links

https://github.com/redtimmy/OAMBuster

JMX RMI – Multiple Applications (RCE)

After achieving a foothold inside the targeted organization, an attacker surely will search for vulnerabilities giving him/her the ability to compromise other machines and move laterally into the network. Especially for companies adopting Java-based software solutions, one of the most abused services to achieve Remote Command Execution is JMX/RMI. It has revealed to be very pervasive in the business LAN/DMZ contexts. Indeed around one year ago we performed a random analysis of both open source and business tools, checking for the presence of JMX/RMI ports. We ended up discovering (and sometimes directly reporting) some new vulnerabilities. Few CVE(s) were registered as well. This whitepaper includes main highlights of our findings.


WHAT IS JMX

JMX (Java Management Extension) is a documental specification for remote management and monitoring of Java applications. Its main unit is the MBean (management bean), a java object exposing some attributes that can be read/written through the network, and most importantly a series of functions or operations invokable from remote. A so-called “MBeanServer” (or more simply JMX Server) keeps track of all registered MBeans inside a kind of searchable register/archive. It is the component puts in charge of managing the communication between clients that want access to one or more exposed functions/attributes of an MBean and the MBean itself.

JMX was not built with the security principle in mind. Therefore, whoever is able to reach the network port it is listening to can also invoke the exposed methods anonymously, without going through a formal authentication process.

WHAT IS RMI

The RMI (Remote Method Invocation) protocol is the most common mechanism (as well as the only one that the JMX standard expressly requires to be supported by default) through which the methods and functions the MBeans remotely expose (made available by means of JMX server) are invoked by clients.

WHERE IS THE PROBLEM WITH JMX/RMI?

By default no authentication is enabled for JMX/RMI. Furthermore the authentication, when rarely adopted, is only restricted to a couple of options:

  • File-based: insecure as passwords are left in clear-text in the filesystem (also transmitted in clear-text over the network);
  • TLS mutual authentication: difficult to set up and maintain with the growth of the numbers of clients and nodes, as it requires the generation of digital keys and certificates for each of them.

The Oracle Java documentation is self-explanatory when it comes to determine where the problem stems from: (https://docs.oracle.com/javase/8/docs/technotes/guides/management/agent.html)

Caution – […] any remote user who knows (or guesses) your port number and host name will be able to monitor and control your Java applications and platform. Furthermore, possible harm is not limited to the operations you define in your MBeans. A remote client could create a “javax.management.loading.MLet” MBean and use it to create new MBeans from arbitrary URLs, at least if there is no security manager. In other words, a rogue remote client could make your Java application execute arbitrary code”.

AFFECTED SOFTWARE

Below follows the list of components and software solutions that we found affected by this specific issue during an analysis conducted in the period February-March 2018.

CISCO UNIFIED CUSTOMER VOICE PORTAL <= 11.x

Cisco Unified CVP is an intelligent IVR (Interactive Voice Response) and call control solution. In its default configuration, until version <= 11.x and potentially above, an unauthenticated JMX/RMI interface is bound to a wildcard address on TCP ports 2098 and 2099. An attacker establishing a network connection to one of these affected ports and sending the malicious payload could easily trigger the RCE.

The vulnerability was first discovered on February 2018. The vendor was made aware almost immediately. After multiple meetings and discussions occurred between April and July 2018, Cisco agreed to document two new security procedures in to its CVP configuration guide:

  • Secure JMX Communication between CVP Components
  • Secure JMX Communication between OAMP and Call Server using Mutual Authentication.

We reopen the dialogue with Cisco on February 2019 when a CVE has been asked but not assigned, as the vendor considers the flaw as a configuration issue.

Anyway Cisco has published a security bulletin for the flaw we reported at the URL https://quickview.cloudapps.cisco.com/quickview/bug/CSCvi31075

NASDAQ BWISE <= 5.x

This is a commercial GRC (Governance, Risk and Compliance Management) solution for risk handling and management. Branch 5.x of Nasdaq BWise is vulnerable because by default the SAP BO Component enables JMX/RMI on TCP port 81 without authentication.

We discovered the vulnerability and contacted the vendor on March 2018. After discussing with them, the release of Service Pack (SP02) has been announced to solve the problem.

A CVE number has not been requested until February 2019, when we realized that in the meantime another security researcher had registered CVE-2018-11247 for the same issue. As indicated in their published security bulletin https://packetstormsecurity.com/files/148918/Nasdaq-BWise-5.0-JMX-RMI-Interface-Remote-Code-Execution.html, the researcher had discovered the vulnerability 2 months after us (May 2018).

However as a CVE already existed, we did not requested a new one.

NICE ENGAGE PLATFORM <= 6.5

NICE Engage is an interaction recording platform. Versions <= 6.5 (and potentially above) open up the TCP port 6338 where a JMX/RMI service listens to without authentication. Of course this may be abused to launch remote commands by deploying a malicious MBean.

On March 4th 2018 we contacted the vendor and on 7th same month they have recognized the vulnerability. They also declared that no specific fix would have been released because enabling the JMX file-based authentication was considered enough to mitigate the finding. Anyway, this change is not reflected in the default configuration and must be applied manually, leaving at risk the companies using the product and are not aware of the problem. Only very recently, February 2019, we have registered CVE-2019-7727 for this vulnerability

APACHE CASSANDRA 3.8 through 3.11.1 and CLOUDERA ZOOKEEPER/CDH 5.X/6.X

On February 2018 we discovered that the Apache Software Foundation project dubbed Cassandra (release between 3.8 and 3.11) exposed the TCP port 7199 on which JMX/RMI was running. We did not report the finding immediately. Soon after someone else did it and registered CVE-2018-8016. All details are perfectly explain here:

https://lists.apache.org/thread.html/bafb9060bbdf958a1c15ba66c68531116fba4a83858a2796254da066@%3Cuser.cassandra.apache.org%3E

During a contextual security investigation on March 2018 we also managed to spot multiple instances of Cloudera Zookeeper/CDH (versions 5.x and 6.x) affected. In this case the TCP port 9010 was exposing a JMX/RMI service. The vendor is aware of the problem at least since June 2018. In one of their release notes they wrote:

A successful attack may leak data, cause denial of service, or even allow arbitrary code execution on the Java process that exposes a JMX port. Beginning in Cloudera Manager 6.1.0, it is possible to configure mutual TLS authentication on ZooKeeper’s JMX port”.

The possibility to configure mutual TLS authentication for previous product versions is unknown instead. We did not register a CVE for this vulnerability.

EXPLOIT CODE

Working tools to exploit JMX/RMI vulnerabilities exist out there. Some good examples are sjet and mjet. When we have started our first investigations in this field did not manage to find one fitting all requirements (we have had problems to target specific contexts and configurations) and have decided to develop our own. This tool is not going to be publicly shared for now. It probably will in future, so visit our blog (https://redtimmysec.wordpress.com).

Moreover, if you want to know more about JMX/RMI exploitation and mitigation, check out our Blackhat Las Vegas courses on 3-4 and 5-6 August 2019, because this will be one of the topics covered there.

Stay tuned!

FlexPaper <= 2.3.6 RCE

Around one year ago we discovered a Remote Command Execution vulnerability on FlexPaper (https://www.flowpaper.com). The vendor was immediately contacted and a CVE registered (2018-11686). However the vulnerability itself has remained undisclosed until now, regardless the fact that a patch has been issued with the release 2.3.7 of the project.

What is Flexpaper

FlexPaper is an open source project, released under GPL license, quite widespread over the internet.  It provides document viewing functionalities to web clients, mobile and tablet devices. At least until 2014 the component has been actively used by WikiLeaks, when it was discovered to be affected by a XSS vulnerability subsequently patched. The remote command execution vulnerability hereby descripted has remained 0day until being reported to vendor in April 2018.

Setup.php

The “php/setup.php” script is used to initialize the Flexpaper configuration file in the “config/” folder. The function “pdf2swfEnabled()” passes the user input unsafely to “exec()” that leads straight to arbitrary command execution.

However, this entry point can be only reached in case Flexpaper has not been initialized (i.e. there is no configuration file in the “config/” folder) which is the main reason to have the software downloaded and installed.

Therefore, after the configuration process is completed, the “exec()” function cannot be hit with arbitrary user input.

File removal via change_config.php

FlexPaper <= 2.3.6 also suffers from an unrestricted file overwrite vulnerability in “php/change_config.php“. The component exposes a functionality to update the configuration file. However, access to this file is improperly guarded, as can be seen in the code snippet below

The “SAVE_CONFIG” is done before the “FLEXPAPER_AUTH” authorization check is performed. Therefore, a not authenticated user can send a POST request and have the configuration file updated. Even more interesting is the fact that after the configuration file is updated, the script will remove all files in the directory that is configured under “path.swf”. As this path was just updated by the attacker, he is in full control of the directory in which he wants to delete files. 

An example of a HTTP request, which results in deletion of the configuration file, is depicted below.

Back to Setup.php

Once the Flexpaper configuration file is deleted, the vulnerable entry point at “setup.php” becomes reachable again. Now the attacker is one GET request far from triggering RCE. The malicious payload is provided to the “PDF2SWF_PATH” parameter. The command is injected just prepending a semicolon “;” character as shown below

In the example above the server was forced to base64 decode a PHP web shell (see following image) and write that in to a file named “tiger_shell.php” in the webserver’s document root.

The web shell

The web shell adopted in this case takes as an input a key and an arbitrary base64 encoded command submitted via GET request. It base64 decode and execute the command only if the key matches with the hardcoded one. From now on, the attacker can launch any arbitrary command like this:

The command injected through “cmd” parameter, for this specific example, is the base64 encoded representation of “id;uname -a;pwd”. Needless to say it can be whatever command the attacker wants to run.

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Some additional notes

During last year we have reported this vulnerability to several broadcasting and media companies that were using the affected component. Some government websites as well.

Exploit code

The exploit has been published here.