CVE-2024-3400: PAN-OS Command Injection Vulnerability in GlobalProtect Gateway. Learn More

CVE-2024-3400: PAN-OS Command Injection Vulnerability in GlobalProtect Gateway. Learn More

Managed Detection & Response

Eliminate active threats with 24/7 threat detection, investigation, and response.

Co-Managed SOC (SIEM)

Maximize your SIEM investment, stop alert fatigue, and enhance your team with hybrid security operations support.

Advisory & Diagnostics

Advance your cybersecurity program and get expert guidance where you need it most.

Penetration Testing

Test your physical locations and IT infrastructure to shore up weaknesses before exploitation.

Database Security

Prevent unauthorized access and exceed compliance requirements.

Email Security

Stop email threats others miss and secure your organization against the #1 ransomware attack vector.

Digital Forensics & Incident Response

Prepare for the inevitable with 24/7 global breach response in-region and available on-site.

Firewall & Technology Management

Mitigate risk of a cyberattack with 24/7 incident and health monitoring and the latest threat intelligence.

Offensive Security
Solutions to maximize your security ROI
Microsoft Exchange Server Attacks
Stay protected against emerging threats
Rapidly Secure New Environments
Security for rapid response situations
Securing the Cloud
Safely navigate and stay protected
Securing the IoT Landscape
Test, monitor and secure network objects
Why Trustwave
About Us
Awards and Accolades
Trustwave SpiderLabs Team
Trustwave Fusion Security Operations Platform
Trustwave Security Colony
Technology Alliance Partners
Key alliances who align and support our ecosystem of security offerings
Trustwave PartnerOne Program
Join forces with Trustwave to protect against the most advance cybersecurity threats
SpiderLabs Blog

Three ModSecurity Rule Language Annoyances

There are three aspects of the ModSecurity Rule Language we are not very happy with. One comes from a wrong design decision (my own), with further two from constraints of working within the framework of Apache. All three break the principle of the intuitive action being the expected one. I am going to document them here and explain how we are planning to mitigate them in future versions:

  1. In a chain starter rule, disruptive actions are processed when the chain matches, but non-disruptive actions are processed when the rule matches. In other words, it is only the disruptive actions that are treated differently in chains, all other action types behave as they would in standalone rules. Have a look at the following:

    SecRule T1 K1 chain,log,block,setvar:tx.counter=+1
    SecRule T2 K2
    In the example above the counter will be incremented if the first rule matches even if the chain doesn't. The blocking action, although defined with the same rule, would only be processed if both the first rule and the second rule match.

    In retrospective, disruptive actions for chains should have been placed with the last rule in a chain, not with the first one. If it is possible to move to that mechanism in the next major version while preserving compatibility with existing configurations we will do that.

  2. SecDefaultAction is valid only for the configuration context in which it is used and is not inherited in child contexts. Configuration contexts are an Apache feature and they come with limitations, one of which is causing this problem.
    SecDefaultAction log,deny
    SecRule T1 K1
    <Location /some/other/path>
    SecRule T2 K2
    In the above example, the first rule blocks, but the second one just uses the ModSecurity defaults and only warns and lets requests through.

    In the next major version of ModSecurity (v3) we will handle our configuration ourselves and this problem will probably go away. In fact, the SecDefaultAction directive might be made obsolete in the next major version because we don't like it much. In retrospective, it was a wrong choice too. It is good practice to write rules to be self-contained. That way they will be easier to understand and maintain, and you don't risk configuration errors due to something being changed in the configuration elsewhere.

  3. Configuration contexts other than <VirtualHost> cannot hold phase 1 rules. Again, this is a limitation of the current implementation that relies on Apache for configuration functionality.

    Short term (e.g. 2.6), we are planning to see if we can detect phase 1 rules in places where they cannot be run and respond with an configuration error. The problem will go away once we start handling our own configuration.

Latest SpiderLabs Blogs

EDR – The Multi-Tool of Security Defenses

This is Part 8 in my ongoing project to cover 30 cybersecurity topics in 30 weekly blog posts. The full series can be found here.

Read More

The Invisible Battleground: Essentials of EASM

Know your enemy – inside and out. External Attack Surface Management tools are an effective way to understand externally facing threats and help plan cyber defenses accordingly. Let’s discuss what...

Read More

Fake Dialog Boxes to Make Malware More Convincing

Let’s explore how SpiderLabs created and incorporated user prompts, specifically Windows dialog boxes into its malware loader to make it more convincing to phishing targets during a Red Team...

Read More