Executive Intelligence Brief

A stored cross-site scripting (XSS) vulnerability exists in Grav CMS versions prior to 2.0.15. The vulnerability is caused by the detectXss() function failing to properly detect event handlers in unpaired quotes in unquoted attribute values. Authenticated editors can inject malicious event handlers, such as onerror=, that can execute in visitor browsers when page content is rendered. The vulnerability has a CVSS score of 8.7 and is classified as HIGH severity. Organizations using Grav CMS should upgrade to version 2.0.15 or later to mitigate this vulnerability.

Threat Overview

Grav is a popular open-source Content Management System (CMS) used for building websites and web applications. It is known for its simplicity, flexibility, and ease of use. The vulnerability affects Grav CMS versions prior to 2.0.15, which means that a large number of websites and web applications built on Grav CMS are potentially vulnerable to this attack.

Technical Deep Dive

Vulnerability Classification

The vulnerability is classified as a stored cross-site scripting (XSS) vulnerability, which is a type of CWE-79 vulnerability. This type of vulnerability occurs when user input is not properly sanitized or validated, allowing an attacker to inject malicious code, such as JavaScript, into a web application.

Root Cause Analysis

The root cause of the vulnerability is the detectXss() function failing to properly detect event handlers in unpaired quotes in unquoted attribute values. This allows an attacker to inject malicious event handlers, such as onerror=, that can execute in visitor browsers when page content is rendered.

Attack Vector & Chain

The attack vector for this vulnerability is a network-based attack, which means that an attacker can exploit the vulnerability by sending a malicious request to the web application. The attack requires the attacker to have low privileges, specifically the ability to edit content as an authenticated editor. The attack also requires user interaction, as the malicious code will only execute when a user visits the affected page.

Exploitation Scenario Walkthrough

Scenario: Stored XSS Attack via Malicious Event Handler Injection

Reconnaissance: An attacker discovers a vulnerable Grav CMS website and identifies an input field that allows user input, such as a comment section or a content editing area.

Weaponization: The attacker prepares a malicious event handler, such as onerror=, that will be injected into the input field.

Delivery & Exploitation: The attacker injects the malicious event handler into the input field, which is then stored in the web application's database. When a user visits the affected page, the malicious code is executed in their browser.

Post-Exploitation: The attacker can use the malicious code to steal user data, take control of the user's session, or perform other malicious actions.

Impact Realization: The final damage is the execution of the malicious code in the user's browser, which can lead to unauthorized access to sensitive data or disruption of service.

Exploitation in the Wild

The vulnerability is not currently being actively exploited in the wild. However, given the severity of the vulnerability and the potential impact, it is likely that attackers will attempt to exploit it in the future.

Impact Analysis

Direct Impact

The direct impact of the vulnerability is the execution of malicious code in a user's browser, which can lead to unauthorized access to sensitive data or disruption of service. The vulnerability has a high impact on confidentiality and integrity, but no impact on availability.

Downstream & Cascading Effects

The downstream and cascading effects of the vulnerability include the potential for lateral movement, data exfiltration, and disruption of service. The vulnerability can also have a significant impact on the reputation of the organization and the trust of its customers.

Affected Products & Versions

The vulnerability affects Grav CMS versions prior to 2.0.15. The following versions are affected:

  • Grav CMS version 0 to 2.0.14

The following version is not affected:

  • Grav CMS version 2.0.15 and later

Detection & Threat Hunting

Indicators of Compromise

The indicators of compromise for this vulnerability include:

  • Unusual user input in the web application's database
  • Malicious code injected into the web application's pages
  • Unexplained changes to the web application's behavior or content

Detection Rules & Signatures

The detection rules and signatures for this vulnerability include:

  • Monitoring for unusual user input in the web application's database
  • Monitoring for malicious code injected into the web application's pages
  • Monitoring for unexplained changes to the web application's behavior or content

Threat Hunting Queries

The threat hunting queries for this vulnerability include:

  • Searching for unusual user input in the web application's database
  • Searching for malicious code injected into the web application's pages
  • Searching for unexplained changes to the web application's behavior or content

Remediation & Hardening

Immediate Actions (0-24 hours)

The immediate actions to remediate this vulnerability include:

  • Upgrading to Grav CMS version 2.0.15 or later
  • Monitoring for unusual user input in the web application's database
  • Monitoring for malicious code injected into the web application's pages

Short-Term Hardening (1-7 days)

The short-term hardening actions include:

  • Implementing additional security controls, such as web application firewalls (WAFs) and intrusion detection systems (IDSs)
  • Enhancing monitoring and logging to detect and respond to potential security incidents

Strategic Recommendations

The strategic recommendations for this vulnerability include:

  • Regularly updating and patching the web application and its components
  • Implementing secure coding practices and secure coding standards
  • Conducting regular security assessments and penetration testing to identify and remediate potential vulnerabilities

Analyst Assessment

The analyst assessment of this vulnerability is that it is a high-severity vulnerability that requires immediate attention. The vulnerability has a high impact on confidentiality and integrity, and it is likely that attackers will attempt to exploit it in the future. Organizations using Grav CMS should upgrade to version 2.0.15 or later to mitigate this vulnerability.

Sources

  • National Vulnerability Database (NVD)
  • Grav CMS Security Advisory