CVE-2026-123198 in LMFDB
Summary
by MITRE • 11/05/2026
LMFDB before commit 01829bd contains a server-side template injection vulnerability in the render_knowl function that allows unauthenticated attackers to inject Jinja expressions via request parameters. Attackers can supply crafted query-string values or 'content' data to /knowledge/render/<ID> to reach Python builtins and execute operating system commands as the web application account.
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Analysis
by VulDB Data Team • 11/05/2026
The LMFDB project, prior to commit 01829bd, suffered from a critical server-side template injection vulnerability located within the render_knowl function of its web application framework. This flaw stems from the improper handling of user-supplied input in Jinja2 templates, specifically when rendering knowledge base entries via the /knowledge/render/<ID> endpoint. The vulnerability allows unauthenticated attackers to inject arbitrary Jinja expressions by manipulating request parameters or providing malicious content data. Because the underlying template engine processes these inputs without adequate sanitization or escaping, it interprets them as executable code rather than static text, creating a direct path for remote code execution.
From a technical perspective, this issue is classified under CWE-94, which covers Improper Control of Generation of Code (Code Injection), and more specifically aligns with CWE-1386 due to the unsafe use of template engines that allow access to dangerous Python objects. The attacker can exploit this by crafting query-string values or POST data containing Jinja2 syntax designed to bypass default security restrictions. By leveraging specific techniques, such as accessing the _class_ and _mro_ attributes of Python objects, an adversary can traverse the object hierarchy to reach built-in types like str or dict. From there, they can access critical methods that allow interaction with the operating system, effectively breaking out of the sandboxed template environment.
The operational impact of this vulnerability is severe, as it leads directly to Remote Code Execution (RCE) under the context of the web application account. An unauthenticated attacker does not need valid credentials to initiate an exploit; they can simply send a crafted HTTP request to the vulnerable endpoint. Once executed, the injected commands run with the same privileges as the LMFDB process, which often includes read and write access to database files, configuration settings, and potentially sensitive user data stored on the server. In worst-case scenarios where the web application runs with elevated system permissions or has network access, this could lead to full compromise of the underlying host infrastructure, allowing for lateral movement within a corporate network or exfiltration of proprietary mathematical databases hosted by LMFDB.
This attack vector maps closely to MITRE ATT&CK technique T1059.007, which describes Command and Scripting Interpretation via Python scripts, as well as T1621, Multi-Factor Authentication Bypass if the application relies on session-based controls that are bypassed by direct API manipulation. The ability to execute operating system commands means an attacker can install backdoors, modify source code, or disrupt service availability through resource exhaustion attacks initiated from within the application layer.
Mitigation for this vulnerability requires immediate patching of the LMFDB instance to a version released after commit 01829bd, which addresses the unsafe rendering logic in the render_knowl function. Developers should ensure that all template variables are properly escaped and that access to Python builtins is restricted within the Jinja2 environment configuration. Additionally, implementing strict input validation on query parameters and content fields can provide an additional layer of defense against injection attempts. For organizations running older versions where immediate patching is not feasible, deploying a Web Application Firewall with rules specifically tuned to detect Jinja2 template injection patterns may help block exploit attempts until the software update can be applied. Regular security audits and static code analysis focused on template engine usage are recommended to prevent similar issues in future development cycles.