Detection: Tomcat Session File Upload Attempt

Updated Date: 2025-03-25 ID: a1d8f5c3-9b7e-4f2d-8c51-3bca5e672410 Author: Michael Haag, Splunk Type: Anomaly Product: Splunk Enterprise Security

Description

This detection identifies potential exploitation of CVE-2025-24813 in Apache Tomcat through the initial stage of the attack. This first phase occurs when an attacker attempts to upload a malicious serialized Java object with a .session file extension via an HTTP PUT request. When successful, these uploads typically result in HTTP status codes 201 (Created) or 409 (Conflict) and create the foundation for subsequent deserialization attacks by placing malicious content in a location where Tomcat's session management can access it.

1
2| tstats count min(_time) as firstTime max(_time) as lastTime from datamodel=Web where Web.http_method=PUT AND Web.uri_path="*.session" AND (Web.status=201 OR Web.status=409) by Web.src, Web.dest, Web.http_user_agent, Web.uri_path, Web.status 
3| `drop_dm_object_name("Web")` 
4| rex field=uri_path "/(?<filename>[^/]+)\.session$" 
5| eval severity="High" 
6| `security_content_ctime(firstTime)` 
7| `security_content_ctime(lastTime)` 
8| `tomcat_session_file_upload_attempt_filter`

Data Source

Name Platform Sourcetype Source
Nginx Access N/A 'nginx:plus:kv' '/var/log/nginx/access.log'

Macros Used

Name Value
security_content_ctime convert timeformat="%Y-%m-%dT%H:%M:%S" ctime($field$)
tomcat_session_file_upload_attempt_filter search *
tomcat_session_file_upload_attempt_filter is an empty macro by default. It allows the user to filter out any results (false positives) without editing the SPL.

Annotations

- MITRE ATT&CK
+ Kill Chain Phases
+ NIST
+ CIS
- Threat Actors
ID Technique Tactic
T1190 Exploit Public-Facing Application Initial Access
T1505.003 Web Shell Persistence
Delivery
Installation
DE.AE
CIS 13

Default Configuration

This detection is configured by default in Splunk Enterprise Security to run with the following settings:

Setting Value
Disabled true
Cron Schedule 0 * * * *
Earliest Time -70m@m
Latest Time -10m@m
Schedule Window auto
Creates Risk Event True
This configuration file applies to all detections of type anomaly. These detections will use Risk Based Alerting.

Implementation

To successfully implement this search, you need to be ingesting logs from your web servers, proxies, or WAFs that process web traffic to Tomcat instances. The data must be mapped to the Web datamodel in the Web node. Ensure your web servers are logging HTTP PUT requests, including status codes and URI paths. This detection specifically looks for PUT requests targeting files with a .session extension that result in HTTP status codes 201 or 409, which indicate successful creation of files - a pattern consistent with the first stage of CVE-2025-24813 exploitation.

Known False Positives

Some legitimate applications might use PUT requests to create .session files, especially in custom implementations that leverage Tomcat's session persistence mechanism. Verify if the detected activity is part of a normal application flow or if it correlates with other suspicious behavior, such as subsequent GET requests with manipulated JSESSIONID cookies.

Associated Analytic Story

Risk Based Analytics (RBA)

Risk Message:

A Tomcat session file upload attempt has been detected from IP $src$ targeting $dest$ with a suspicious .session file. This could indicate the first stage of CVE-2025-24813 exploitation.

Risk Object Risk Object Type Risk Score Threat Objects
dest system 70 src

References

Detection Testing

Test Type Status Dataset Source Sourcetype
Validation ✅ Passing N/A N/A N/A
Unit ✅ Passing Dataset nginx nginx:plus:kv
Integration ✅ Passing Dataset nginx nginx:plus:kv

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: GitHub | Version: 1