CVE-2026-44267 in Elo
Summary
by MITRE • 11/03/2026
Elo is a purely functional expression language for no-code tools. Prior to 1.0.1, plain Elo strings supplied to defaultFormats.elo.parse(), bin/elo, or elo-lang.org/try can use .constructor.constructor to reach JavaScript Function because the member_access handler in src/transform.ts does not reject meta-properties, src/compilers/javascript.ts emits the surviving property directly, and src/parser.ts accepts constructor as an ordinary identifier. The resulting generated JavaScript executes attacker-selected code in the host runtime. This permits browser script execution and session compromise on the auto-running playground and arbitrary Node.js code execution on library, CI, or DevOps hosts. This plain-string path is distinct from the programmatic AST-object injection issue. This issue is fixed in version 1.0.1.
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Analysis
by VulDB Data Team • 11/03/2026
The Elo expression language, designed as a purely functional tool for no-code environments, suffered from a critical server-side code execution vulnerability due to insufficient input validation and unsafe property access handling within its parsing and compilation pipeline. Prior to the release of version 1.0.1, the system failed to adequately sanitize or restrict meta-properties such as constructor during the evaluation of plain Elo strings. This flaw allowed attackers to bypass intended functional constraints by leveraging JavaScript's prototype chain mechanisms to escalate from simple data manipulation to arbitrary code execution within the host runtime environment.
The technical root cause lies in a combination of failures across three core components of the Elo engine: src/parser.ts, src/transform.ts, and src/compilers/javascript.ts. The parser incorrectly accepted constructor as an ordinary identifier rather than treating it as a restricted meta-property that could lead to prototype pollution or access. Subsequently, the transform module's member_access handler failed to reject these dangerous meta-properties during the transformation phase. Finally, the JavaScript compiler emitted the surviving property directly into the generated code without any sanitization checks. This chain of failures enabled an attacker to inject .constructor.constructor chains into plain Elo strings, which resolved to the global Function constructor in JavaScript, thereby allowing the execution of arbitrary commands.
The operational impact of this vulnerability is severe and varies depending on the deployment context of the Elo engine. In browser-based environments, such as the auto-running playground hosted at elo-lang.org/try, an attacker could execute malicious scripts directly within the user's session. This capability facilitates cross-site scripting-like attacks that can lead to session hijacking, credential theft, or defacement of the application interface. When deployed in server-side contexts using Node.js libraries, continuous integration pipelines, or DevOps automation hosts, the vulnerability allows for arbitrary code execution on the host machine. This level of access permits attackers to exfiltrate sensitive data, install backdoors, pivot to other systems within the network, and completely compromise the integrity and availability of the hosting infrastructure.
This specific attack vector is distinct from programmatic Abstract Syntax Tree injection issues because it exploits the parsing of plain text strings rather than manipulating structured object inputs programmatically. The vulnerability aligns with CWE-94 Improper Control of Generation of Code or Script, specifically code injection via unsafe evaluation mechanisms, and maps to MITRE ATT&CK techniques related to Command and Scripting Interpreter abuse for remote access and execution. To mitigate this risk, organizations must immediately upgrade the Elo library to version 1.0.1 or later where these input validation checks have been implemented. Additionally, developers should implement strict allow-lists for property names during parsing and avoid using eval-like patterns in any custom extensions of the language engine.