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Description

The following analytic identifies activity related to Text4Shell, or the critical vulnerability CVE-2022-42889 in Apache Commons Text Library. Apache Commons Text versions 1.5 through 1.9 are affected, but it has been patched in version 1.10. The analytic may need to be tuned for your environment before enabling as a TTP, or direct Notable. Apache Commons Text is a Java library described as a library focused on algorithms working on strings. We can see it as a general-purpose text manipulation toolkit. This vulnerability affects the StringSubstitutor interpolator class, which is included in the Commons Text library. A default interpolator allows for string lookups that can lead to Remote Code Execution. This is due to a logic flaw that makes the script, dns, and url lookup keys interpolated by default, as opposed to what it should be, according to the documentation of the StringLookupFactory class. Those keys allow an attacker to execute arbitrary code via lookups.

  • Type: Anomaly
  • Product: Splunk Enterprise, Splunk Enterprise Security, Splunk Cloud
  • Datamodel: Web
  • Last Updated: 2022-10-26
  • Author: Michael Haag, Splunk
  • ID: 19a481e0-c97c-4d14-b1db-75a708eb592e

Annotations

ATT&CK

ATT&CK

ID Technique Tactic
T1505.003 Web Shell Persistence
T1505 Server Software Component Persistence
T1190 Exploit Public-Facing Application Initial Access
Kill Chain Phase
  • Exploitation
NIST
  • DE.CM
CIS20
  • CIS 3
  • CIS 5
  • CIS 16
CVE
ID Summary CVSS
CVE-2022-42889 Apache Commons Text performs variable interpolation, allowing properties to be dynamically evaluated and expanded. The standard format for interpolation is "${prefix:name}", where "prefix" is used to locate an instance of org.apache.commons.text.lookup.StringLookup that performs the interpolation. Starting with version 1.5 and continuing through 1.9, the set of default Lookup instances included interpolators that could result in arbitrary code execution or contact with remote servers. These lookups are: - "script" - execute expressions using the JVM script execution engine (javax.script) - "dns" - resolve dns records - "url" - load values from urls, including from remote servers Applications using the interpolation defaults in the affected versions may be vulnerable to remote code execution or unintentional contact with remote servers if untrusted configuration values are used. Users are recommended to upgrade to Apache Commons Text 1.10.0, which disables the problematic interpolators by default. None
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| tstats `security_content_summariesonly` count min(_time) as firstTime max(_time) as lastTime from datamodel=Web where Web.http_method IN (POST, GET) by Web.src Web.status Web.uri_path Web.dest Web.http_method Web.uri_query Web.http_user_agent 
| `drop_dm_object_name("Web")` 
| eval utf=if(like(lower(uri_query),"%:utf-8:http%"),2,0) 
| eval lookup = if(like(lower(uri_query), "%url%") OR like(lower(uri_query), "%dns%") OR like(lower(uri_query), "%script%"),2,0) 
| eval other_lookups = if(like(lower(uri_query), "%env%") OR like(lower(uri_query), "%file%") OR like(lower(uri_query), "%java%") OR like(lower(uri_query), "%localhost%") OR like(lower(uri_query), "%properties%") OR like(lower(uri_query), "%resource%") OR like(lower(uri_query), "%sys%") OR like(lower(uri_query), "%xml%") OR like(lower(uri_query), "%base%"),1,0) 
| addtotals fieldname=Score utf lookup other_lookups 
| fields Score, src, dest, status, uri_query, uri_path, http_method, http_user_agent firstTime lastTime 
| `security_content_ctime(firstTime)` 
| `security_content_ctime(lastTime)` 
| where Score >= 4 
| `exploit_public_facing_application_via_apache_commons_text_filter`

Macros

The SPL above uses the following Macros:

:information_source: exploit_public_facing_application_via_apache_commons_text_filter is a empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Supported Add-on (TA)

List of Splunk Add-on’s tested to work with the analytic.

Required fields

List of fields required to use this analytic.

  • _time
  • Web.http_method
  • Web.src
  • Web.dest
  • Web.http_user_agent
  • Web.status
  • Web.uri_query
  • Web.uri_path

How To Implement

To implement, one must be collecting network traffic that is normalized in CIM and able to be queried via the Web datamodel. Or, take the chunks out needed and tie to a specific network source type to hunt in. Tune as needed, or remove the other_lookups statement.

Known False Positives

False positives are present when the values are set to 1 for utf and lookup. It's possible to raise this to TTP (direct notable) if removal of other_lookups occur and Score is raised to 2 (down from 4).

Associated Analytic Story

RBA

Risk Score Impact Confidence Message
49.0 70 70 A URL was requested related to Text4Shell on $dest$ by $src$.

:information_source: The Risk Score is calculated by the following formula: Risk Score = (Impact * Confidence/100). Initial Confidence and Impact is set by the analytic author.

Reference

Test Dataset

Replay any dataset to Splunk Enterprise by using our replay.py tool or the UI. Alternatively you can replay a dataset into a Splunk Attack Range

source | version: 1