CVE-2025-1686: Pebble Templates Path Traversal Flaw

CVE-2025-1686 Overview

CVE-2025-1686 is a Path Traversal vulnerability affecting all versions of the io.pebbletemplates:pebble Java templating library. The vulnerability exists in the include tag functionality, which allows external control of file names or paths. A high-privileged attacker can exploit this flaw to access sensitive local files by crafting malicious notification templates that leverage the include tag to read arbitrary files from the filesystem.

Critical Impact

High-privileged attackers can read sensitive system files such as /etc/passwd or /proc/1/environ through crafted Pebble templates, potentially exposing credentials, configuration data, and other sensitive information.

Affected Products

• Pebbletemplates Pebble (all versions)
• Applications using io.pebbletemplates:pebble dependency
• Systems allowing user-controlled Pebble template content

Discovery Timeline

• 2025-02-27 - CVE-2025-1686 published to NVD
• 2025-12-19 - Last updated in NVD database

Technical Details for CVE-2025-1686

Vulnerability Analysis

This vulnerability falls under CWE-73 (External Control of File Name or Path), a class of security weaknesses where user-controlled input can influence file system operations. In the context of Pebble Templates, the include tag is designed to incorporate the contents of other template files into the current template during rendering. However, the implementation lacks sufficient validation of the file paths being requested.

When a privileged user has the ability to create or modify Pebble templates, they can abuse the include tag to specify arbitrary file paths on the server filesystem. This transforms a template inclusion mechanism into a Local File Inclusion (LFI) vulnerability. The attack requires high privileges to craft and deploy malicious templates, but once executed, it can expose critical system information.

Root Cause

The root cause of this vulnerability is insufficient input validation and path sanitization in the Pebble template engine's include tag implementation. The tag does not properly restrict file paths to a safe directory or validate that requested files are within an expected template directory. This allows path traversal sequences and absolute paths to be used, enabling access to files outside the intended template scope.

Attack Vector

The attack is network-based and requires high privileges to execute. An attacker with the ability to create or modify Pebble templates can craft a malicious template that uses the include tag to read sensitive files from the server's filesystem. The attack flow involves:

1. The attacker gains access to a system where they can create or modify Pebble templates
2. The attacker creates a template containing an include directive pointing to a sensitive file
3. When the template is rendered by the application, the contents of the targeted file are included in the output
4. The attacker retrieves the rendered output containing the sensitive file contents

A malicious template might include directives targeting files such as /etc/passwd for user enumeration, /proc/1/environ for environment variables that may contain secrets, or application configuration files containing database credentials.

Detection Methods for CVE-2025-1686

Indicators of Compromise

• Template files containing suspicious include tags with absolute paths or path traversal sequences (../)
• Templates referencing system files like /etc/passwd, /etc/shadow, or /proc/ paths
• Unusual file access patterns in application logs showing reads to system configuration files
• Template rendering outputs containing unexpected system file contents

Detection Strategies

• Implement file integrity monitoring on template directories to detect unauthorized modifications
• Configure application logging to capture template rendering operations and included file paths
• Deploy Web Application Firewall (WAF) rules to detect path traversal patterns in template-related requests
• Monitor for access to sensitive system files from the application's process context

Monitoring Recommendations

• Enable audit logging for template creation and modification events
• Set up alerts for template includes referencing paths outside designated template directories
• Monitor application error logs for file access failures that may indicate exploitation attempts
• Review template content during security audits for suspicious include directives

How to Mitigate CVE-2025-1686

Immediate Actions Required

• Audit all existing Pebble templates for suspicious include tag usage
• Implement the recommended workaround to disable the include tag if not required
• Restrict template creation and modification privileges to trusted users only
• Review application logs for signs of exploitation

Patch Information

As of the last update, all versions of Pebble Templates are affected. A fix has been proposed via GitHub Pull Request #715. Organizations should monitor the vendor advisory for official patch releases and apply updates as soon as they become available. Additional technical details can be found in the Snyk vulnerability database.

Workarounds

• Disable the include tag in Pebble Templates using the extension customizer API
• Implement a custom template loader that validates and restricts accessible paths
• Run the application with minimal filesystem permissions to limit exposure
• Use containerization to isolate the application filesystem from sensitive host files

// Mitigation: Disable the include tag in Pebble Templates
new PebbleEngine.Builder()
    .registerExtensionCustomizer(new DisallowExtensionCustomizerBuilder()
        .disallowedTokenParserTags(List.of("include"))
        .build())
    .build();