CVE-2016-3081

Apache Struts is a web application framework. This flaw lets an outsider send a crafted web request that tricks the server into calling methods it shouldn’t—essentially allowing code to run on your server. Think of it like a receptionist that can be tricked into opening a door to an area it’s supposed to lock, without needing a key.

This matters if your business runs a website or web application built on Apache Struts (or software that embeds it). Your risk is specifically tied to running Apache Struts versions 2.3.19 through 2.3.28 with Dynamic Method Invocation enabled. It becomes a risk when the affected feature is enabled and the attacker can reach the web application over the network (no login is required).

This is urgent because it allows unauthenticated remote attackers to run arbitrary code, and an exploit module exists and is known to be weaponized. Even though there’s no KEV listing from CISA, the vulnerability’s exposure conditions (DMI enabled, network-reachable) make it a practical threat for exposed web apps, so you should address it now rather than later.

1. Confirm exposure

   • Identify which application(s) use Apache Struts and the exact Struts version (the vulnerable range is 2.3.19 to 2.3.28).
   • Verify whether Dynamic Method Invocation is enabled in your Struts configuration. The findings specifically say the issue is reachable when Dynamic Method Invocation is enabled.
   • If you use a dependency manager (Maven/Gradle), confirm the resolved org.apache.struts:struts2-core version at build/runtime.

2. Upgrade to the fixed versions

   • Update org.apache.struts:struts2-core to one of the fixed releases:
     • Upgrade to 2.3.20.3 if you are on/near the 2.3.20.x line.
     • Upgrade to 2.3.24.3 if you are on/near the 2.3.24.x line.
     • Upgrade to 2.3.28.1 if you are on/near the 2.3.28.x line.
   • After upgrading, run your application’s functional tests, especially any routing/action invocation paths, to ensure there are no configuration regressions.

3. Temporary workaround (if patching is delayed)

   • Disable Dynamic Method Invocation and verify that method:-style invocation is no longer accepted/processed as it was before.
   • Re-check configuration after any deployment or configuration reload.

4. Monitor and verify

   • Review web server and application logs for suspicious requests that resemble method: prefixed inputs.
   • If you find any suspicious activity, treat it as potentially serious compromise: assume attacker code execution may have occurred until verified otherwise.

5. Communication

   • Notify the business owner of status (affected/not affected), the chosen upgrade target version, and the ETA for completion.

CVE-2016-3081 is a high-severity issue (CWE-77) affecting Apache Struts 2.3.19 through 2.3.28 when Dynamic Method Invocation is enabled. Mechanism: a remote attacker can trigger arbitrary code execution by sending input starting with the method: prefix; the payload is processed through chained expression handling in a way that turns what should be controlled method invocation into attacker-controlled execution.

Exploit/exposure signals from the findings:

• Authentication is not required.
• No user interaction is required.
• The findings state it is reachable in the default configuration when Dynamic Method Invocation is enabled.
• Weaponization: a Metasploit module is known (7 known).
• KEV: not listed in CISA KEV.
• Patch guidance from findings: fixed versions are 2.3.20.3, 2.3.24.3, and 2.3.28.1 for org.apache.struts:struts2-core.

ETP/likelihood note: the findings include a predicted likelihood figure, but public guidance here focuses on the confirmed weaponization and straightforward exposure conditions rather than prediction.