CVE-2025-9556 in Langchaingo
Summary
by MITRE • 09/12/2025
Langchaingo supports the use of jinja2 syntax when parsing prompts, which is in turn parsed using the gonja library v1.5.3. Gonja supports include and extends syntax to read files, which leads to a server side template injection vulnerability within langchaingo, allowing an attacker to insert a statement into a prompt to read the "etc/passwd" file.
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Analysis
by VulDB Data Team • 09/12/2025
This vulnerability exists within the langchaingo library which facilitates integration with various language models and supports jinja2 template syntax for prompt parsing. The underlying implementation utilizes the gonja library version 1.5.3 which inherently supports advanced template features including include and extends directives. These directives enable template files to reference and incorporate content from external files, creating a pathway for malicious exploitation when user-supplied prompts are processed through the template engine without proper sanitization. The vulnerability stems from the lack of input validation and proper template security controls within the prompt processing pipeline, allowing attackers to inject malicious template syntax that leverages the include directive to access arbitrary files on the server filesystem. When an attacker crafts a prompt containing jinja2 syntax with include directives pointing to sensitive system files like /etc/passwd, the gonja template engine executes this injection, resulting in unauthorized file access and potential information disclosure. This represents a server-side template injection vulnerability that can be categorized under CWE-94 as improper control of generation of code and falls within the ATT&CK technique T1213.002 for Data from Information Repositories. The impact extends beyond simple file reading as it could potentially allow attackers to access configuration files, credentials, or other sensitive data stored on the server. The vulnerability is particularly concerning because it operates at the template parsing layer, meaning that even seemingly benign user input can be transformed into malicious file access requests through carefully crafted jinja2 syntax. Organizations using langchaingo for prompt processing should be aware that this vulnerability can be exploited without requiring special privileges or complex attack vectors, making it a significant risk to applications that process untrusted user input through template-based prompt systems. The security implications are compounded by the fact that the vulnerability exists in the core template processing functionality rather than in application-specific code, meaning that any application utilizing langchaingo for prompt handling is potentially exposed to this attack vector. Remediation requires either upgrading to a version of gonja that properly sanitizes template inputs or implementing strict input validation and template security controls to prevent the execution of potentially malicious include directives within user-supplied prompts. Organizations should also consider implementing network segmentation and monitoring for unusual file access patterns that might indicate exploitation attempts.
The technical flaw manifests in the template engine's insufficient validation of user-provided content, particularly when processing jinja2 syntax that includes file inclusion directives. The gonja library v1.5.3 does not adequately restrict the paths that can be referenced through include and extends statements, allowing attackers to traverse the filesystem and access sensitive files. This vulnerability demonstrates the dangerous intersection of template flexibility and security oversight, where the very features designed to enable powerful template functionality become attack vectors when not properly constrained. The attack surface is broad as any application relying on langchaingo for prompt processing is susceptible to this issue, particularly those that accept user-generated prompts for processing through language model interfaces. The vulnerability's exploitation is straightforward and requires minimal skill, making it attractive to threat actors seeking to extract sensitive information from systems. Security controls that should be implemented include strict template sandboxing, path validation, and input sanitization to prevent the execution of file inclusion directives in user-provided content. Organizations should also consider implementing principle of least privilege for template processing components and monitoring for unauthorized file access attempts. This vulnerability exemplifies the critical importance of security considerations in template processing libraries and highlights the need for comprehensive input validation even in systems designed for flexibility and extensibility. The potential for escalation exists if attackers can access configuration files or credentials stored in accessible locations, making this vulnerability particularly dangerous in environments where the language model interface has access to sensitive system resources.