Detection rules › Splunk
Log4Shell JNDI Payload Injection Attempt
The following analytic identifies attempts to inject Log4Shell JNDI payloads via web calls. It leverages the Web datamodel and uses regex to detect patterns like ${jndi:ldap:// in raw web event data, including HTTP headers. This activity is significant because it targets vulnerabilities in Java web applications using Log4j, such as Apache Struts and Solr. If confirmed malicious, this could allow attackers to execute arbitrary code, potentially leading to full system compromise. Immediate investigation is required to determine if the attempt was successful and to mitigate any potential exploitation.
MITRE ATT&CK coverage
| Tactic | Techniques |
|---|---|
| Initial Access | T1133 External Remote Services, T1190 Exploit Public-Facing Application |
| Persistence | T1133 External Remote Services |
Rule body splunk
name: Log4Shell JNDI Payload Injection Attempt
id: c184f12e-5c90-11ec-bf1f-497c9a704a72
version: 9
creation_date: '2021-12-13'
modification_date: '2026-05-13'
author: Jose Hernandez
status: production
type: Anomaly
description: The following analytic identifies attempts to inject Log4Shell JNDI payloads via web calls. It leverages the Web datamodel and uses regex to detect patterns like `${jndi:ldap://` in raw web event data, including HTTP headers. This activity is significant because it targets vulnerabilities in Java web applications using Log4j, such as Apache Struts and Solr. If confirmed malicious, this could allow attackers to execute arbitrary code, potentially leading to full system compromise. Immediate investigation is required to determine if the attempt was successful and to mitigate any potential exploitation.
data_source:
- Nginx Access
search: |-
| from datamodel Web.Web
| regex _raw="[jJnNdDiI]{4}(\:|\%3A|\/|\%2F)\w+(\:\/\/|\%3A\%2F\%2F)(\$\{.*?\}(\.)?)?"
| fillnull
| stats count by action, category, dest, dest_port, http_content_type, http_method, http_referrer, http_user_agent, site, src, url, url_domain, user
| `log4shell_jndi_payload_injection_attempt_filter`
how_to_implement: This detection requires the Web datamodel to be populated from a supported Technology Add-On like Splunk for Apache or Splunk for Nginx.
known_false_positives: If there is a vulnerablility scannner looking for log4shells this will trigger, otherwise likely to have low false positives.
references:
- https://www.lunasec.io/docs/blog/log4j-zero-day/
drilldown_searches:
- name: View the detection results for - "$user$" and "$dest$"
search: '%original_detection_search% | search user = "$user$" dest = "$dest$"'
earliest_offset: $info_min_time$
latest_offset: $info_max_time$
- name: View risk events for the last 7 days for - "$user$" and "$dest$"
search: '| from datamodel Risk.All_Risk | search normalized_risk_object IN ("$user$", "$dest$") | stats count min(_time) as firstTime max(_time) as lastTime values(search_name) as "Search Name" values(risk_message) as "Risk Message" values(analyticstories) as "Analytic Stories" values(annotations._all) as "Annotations" values(annotations.mitre_attack.mitre_tactic) as "ATT&CK Tactics" by normalized_risk_object | `security_content_ctime(firstTime)` | `security_content_ctime(lastTime)`'
earliest_offset: 7d
latest_offset: "0"
intermediate_findings:
entities:
- field: user
type: user
score: 20
message: CVE-2021-44228 Log4Shell triggered for host $dest$
- field: dest
type: system
score: 20
message: CVE-2021-44228 Log4Shell triggered for host $dest$
analytic_story:
- Log4Shell CVE-2021-44228
- CISA AA22-257A
- CISA AA22-320A
asset_type: Endpoint
cve:
- CVE-2021-44228
mitre_attack_id:
- T1190
- T1133
product:
- Splunk Enterprise
- Splunk Enterprise Security
- Splunk Cloud
category: web
security_domain: threat
tests:
- name: True Positive Test
attack_data:
- data: https://media.githubusercontent.com/media/splunk/attack_data/master/datasets/attack_techniques/T1190/log4j_proxy_logs/log4j_proxy_logs.log
source: nginx
sourcetype: nginx:plus:kv
test_type: unit
Stages and Predicates
Stage 1: search
| from datamodel Web.Web
Stage 2: regex
| regex _raw="[jJnNdDiI]{4}(\:|\%3A|\/|\%2F)\w+(\:\/\/|\%3A\%2F\%2F)(\$\{.*?\}(\.)?)?"
Stage 3: fillnull
| fillnull
Stage 4: stats
| stats count by action, category, dest, dest_port, http_content_type, http_method, http_referrer, http_user_agent, site, src, url, url_domain, user
Stage 5: search
| `log4shell_jndi_payload_injection_attempt_filter`
Indicators
Each row is a field, operator, and value that the rule matches. The corpus column counts how many other rules in the catalog look for the same combination: high numbers point to widely-used, community-vetted indicators. Blank or 1 shows that the indicator is specific to this rule.
| Field | Kind | Values |
|---|---|---|
_raw | regex_match |
|
Search terms
Bare-string tokens in the SPL search body. Splunk matches each token against _raw (the untyped raw event text) anywhere it appears, not against a specific field. These don't surface in the Indicators table because they aren't predicates on a known field.
| Stage | Term |
|---|---|
| 1 | from |
| 1 | datamodel |
| 1 | Web.Web |