# CVE-2026-33941: Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options > Attackers can inject arbitrary JavaScript into Handlebars.js CLI precompiler output via unescaped filenames or options, leading to code execution. - **Severity:** High 8.3 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Any signed-in user - **Attackable:** Local or same network only - **Victim action needed:** A user has to click or open something - **Fix available:** Yes - **Published:** 27 Mar 2026 - **Updated:** 11 Sep 2026 - **Also known as:** CLEANSTART-2026-IF99885, CLEANSTART-2026-SZ10382, DEBIAN-CVE-2026-33941, GHSA-xjpj-3mr7-gcpf, MINI-2fq2-pv58-m848, MINI-5h5g-6g95-p5w6, MINI-5q7f-r999-mppr, MINI-6wjf-x49m-74mf, MINI-75gp-g7mh-x45q, MINI-7cvr-wgvg-725p, MINI-7hmh-68wh-j7hh, MINI-7qm3-f8q2-542c, MINI-857q-cq8m-8hx2, MINI-cw5q-p3rx-fr3r, MINI-f67w-wpx7-xmwm, MINI-g4r5-5jhv-4m86, MINI-hqgj-w9jw-hx2f, MINI-x8c8-mfff-34fq, ROOT-APP-NPM-CVE-2026-33941, UBUNTU-CVE-2026-33941 ## What is CVE-2026-33941? CVE-2026-33941 is a high-severity code injection vulnerability in handlebars-lang handlebars.js, published on 27 Mar 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link. ### Official description Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the Handlebars CLI precompiler (`bin/handlebars` / `lib/precompiler.js`) concatenates user-controlled strings — template file names and several CLI options — directly into the JavaScript it emits, without any escaping or sanitization. An attacker who can influence template filenames or CLI arguments can inject arbitrary JavaScript that executes when the generated bundle is loaded in Node.js or a browser. Version 4.7.9 fixes the issue. Some workarounds are available. First, validate all CLI inputs before invoking the precompiler. Reject filenames and option values that contain characters with JavaScript string-escaping significance (`"`, `'`, `;`, etc.). Second, use a fixed, trusted namespace string passed via a configuration file rather than command-line arguments in automated pipelines. Third, run the precompiler in a sandboxed environment (container with no write access to sensitive paths) to limit the impact of successful exploitation. Fourth, audit template filenames in any repository or package that is consumed by an automated build pipeline. Weakness: CWE-94 (Improper Control of Generation of Code), CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output) ## Which versions are affected by CVE-2026-33941? 2 open source packages ship an affected version, including handlebars. It affects 1 product. | Package | Ecosystem | Affected | Fixed in | | --- | --- | --- | --- | | `handlebars` | npm | From 4.0.0 | 4.7.9 | | `handlebars` | npm | From 4.0.0 | 4.7.9 | Products: Handlebarsjs Handlebars. ## How do I fix CVE-2026-33941? Upgrade handlebars to 4.7.9 or later. ## Is CVE-2026-33941 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33941 exists. ## Other vulnerabilities in handlebars-lang handlebars.js - [CVE-2026-33937](https://insights.sbomify.com/CVE-2026-33937/): Handlebars.js has JavaScript Injection via AST Type Confusion (critical 9.8) - [CVE-2026-33938](https://insights.sbomify.com/CVE-2026-33938/): Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block (high 8.1) - [CVE-2026-33940](https://insights.sbomify.com/CVE-2026-33940/): Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial (high 8.1) - [CVE-2019-20920](https://insights.sbomify.com/CVE-2019-20920/): Arbitrary Code Execution in Handlebars (high 8.1) - [CVE-2026-33939](https://insights.sbomify.com/CVE-2026-33939/): Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation (high 7.5) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-33941 and fix it if it is affected. What it is: CVE-2026-33941 is a high-severity code injection vulnerability in handlebars-lang handlebars.js, published on 27 Mar 2026. It can only be exploited from the same machine or local network, and only if a user opens a file or follows a link. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33941 exists. Affected packages and fixed versions: - handlebars (npm): affected from 4.0.0; fixed in 4.7.9 - handlebars (npm): affected from 4.0.0; fixed in 4.7.9 Task: 1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies. 2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it. 3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead. 4. Run the tests and summarise what changed and why. 5. If nothing in the project is affected, say so and change nothing. Reference: https://insights.sbomify.com/CVE-2026-33941/ (Markdown: https://insights.sbomify.com/CVE-2026-33941/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33941 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33941 - OSV: https://osv.dev/vulnerability/CVE-2026-33941 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-33941/ Summaries are generated and may contain mistakes; the official description above is the record.