I found that security and privacy section of this company’s website was vulnerable to command execution. I informed them about this issue and their security team was able to confirm it. They added me to their hall of fame and were able to fix the issue quickly. My overall experience of working with them was very pleasant.
One fine evening, while exploring an organization’s Security and Privacy page, I don’t remember how I came across a java stack trace. The last paragraph, after the stack trace caught my attention. It said –
“You are seeing this page because development mode is enabled. To disable this mode, set struts.devmode=false”.
I googled the error message but could not find anything relevant. Then, I searched for “struts dev mode” and somehow, landed at Pwntester’s insightful blog on OGNL Injection via struts dev mode, (as well as a few other links on the command execution capability of the dev mode setting).
OGNL is an expression language for Java which allows getting and setting JavaBeans properties, on the fly (using java reflection). It also allows execution of methods of Java classes.
Struts2 comes with an inbuilt OGNL debug console named as dev mode, to help developers with more verbose logs. This can also be used in testing OGNL expressions. Dev mode is disabled by default. If enabled, this setting uses debugging interceptor and supports four types of debug parameters.
- debug = console
(non-intrusive way to confirm an enabled devmode setting. It will open a new window with a black background webconsole which can further be used for OGNL expression testing.)
- debug = browser
(non-intrusive way to confirm an enabled devmode setting. it will show the properties of the specified object value e.g. debug=browser&object=%23parameters)
- debug = xml
- debug = command
(this is used to execute the intended OGNL payload.)
By using parameter debug=command and passing the specially crafted OGNL payload as ‘expression‘ parameter, a command execution can be achieved. e.g. As shown in the below URL, debug and expression parameters are passed to a Struts Action, HelloWorld.action.
Mitigation and Remediation:
Always disable devMode in production. Apache also mentions this in their security tips. Best way is to ensure the following setting is applied to your
struts.xml in production:
<constant name ="struts.devMode" value="false" />
While by-default devMode is set to ‘False’, many applications enable this setting in their non-prod environment for verbose logs and forget to disable it when deploying to Prod.
8/26/2018 – Reported the issue to this organization
8/28/2018 – They acknowledged the report and confirmed that it was a valid issue and was not previously reported either internally or externally.
10/08/2018 – They fixed the issue and asked me to validate it.
10/08/2018 – They added me to their security hall of fame list.
05/02/2019 – Draft blog post shared with them
05/03/2019 – Organization said they need time to review it
06/20/2019 – Followed up with the them
06/25/2019 – They wrote that they were still reviewing the post
07/11/2019 – Followed up with the organization, received no response
07/22/2019 – Followed up with the organization, received no response
08/16/2019 – Followed up with the organization, received no response
08/22/2019 – Followed up with the organization, received no response
11/13/2019 – Followed up with the organization, no response from their side
11/16/2019 – Published this post but without any name.