Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options

CISA KEV is observed exploitation evidence. FIRST EPSS is a dated prediction of exploitation in the next 30 days. Missing scores are unknown. This collector requests predictions only for explicit CVE aliases in the public NuGet archive; Microsoft release views retain their existing prediction scope.

No collected risk observation for these identifiers. This does not establish absence of exploitation or a zero probability.

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.

Source published

27 Mar 2026 21:13:15 UTC

Source modified

11 Sep 2026 12:09:10 UTC

Observed here

23 Oct 2026 15:48:27 UTC

Source terms

CVE Program Terms of Use

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: cve-program · CVE Program Terms of Use. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · 8.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

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.

Source published

Mar 27, 2026, 9:13:15 PM (timezone not stated)

Source modified

Sep 11, 2026, 12:09:10 PM (timezone not stated)

Observed here

1 Nov 2026 06:05:02 UTC

Source terms

ENISA EUVD · source terms and attribution apply

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This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: euvd · ENISA EUVD · source terms and attribution apply. Source text is retained; field grouping and change labels are provided by ChangeIntel.

EUVD CVSS 3.1 · 8.3 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

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.

Source published

27 Mar 2026 22:16:21 UTC

Source modified

26 Oct 2026 22:10:00 UTC

Observed here

27 Oct 2026 09:03:00 UTC

Source terms

NIST NVD usage terms; underlying source attribution retained

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: nvd · NIST NVD usage terms; underlying source attribution retained. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS 3.1 · [email protected] · Secondary · 8.2 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

CVSS 3.1 · [email protected] · Primary · 8.2 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

CVSS 3.1 · 0b0ca135-0b70-47e7-9f44-1890c2a1c46c · Secondary · 8.2 CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

## Summary 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. ## Description `lib/precompiler.js` generates JavaScript source by string-interpolating several values directly into the output. Four distinct injection points exist: ### 1. Template name injection ```javascript // Vulnerable code pattern output += 'templates["' + template.name + '"] = template(...)'; ``` `template.name` is derived from the file system path. A filename containing `"` or `'];` breaks out of the string literal and injects arbitrary JavaScript. ### 2. Namespace injection (`-n` / `--namespace`) ```javascript // Vulnerable code pattern output += 'var templates = ' + opts.namespace + ' = ' + opts.namespace + ' || {};'; ``` `opts.namespace` is emitted as raw JavaScript. Anything after a `;` in the value becomes an additional JavaScript statement. ### 3. CommonJS path injection (`-c` / `--commonjs`) ```javascript // Vulnerable code pattern output += 'var Handlebars = require("' + opts.commonjs + '");'; ``` `opts.commonjs` is interpolated inside double quotes with no escaping, allowing `"` to close the string and inject further code. ### 4. AMD path injection (`-h` / `--handlebarPath`) ```javascript // Vulnerable code pattern output += "define(['" + opts.handlebarPath + "handlebars.runtime'], ...)"; ``` `opts.handlebarPath` is interpolated inside single quotes, allowing `'` to close the array element. All four injection points result in code that executes when the generated bundle is `require()`d or loaded in a browser. ## Proof of Concept **Template name vector (creates a file `pwned` on disk):** ```bash mkdir -p templates printf 'Hello' > "templates/evil'] = (function(){require(\"fs\").writeFileSync(\"pwned\",\"1\")})(); //.handlebars" node bin/handlebars templates -o out.js node -e 'require("./out.js")' # Executes injected code, creates ./pwned ``` **Namespace vector:** ```bash node bin/handlebars templates -o out.js \ -n "App.ns; require('fs').writeFileSync('pwned2','1'); //" node -e 'require("./out.js")' ``` **CommonJS vector:** ```bash node bin/handlebars templates -o out.js \ -c 'handlebars"); require("fs").writeFileSync("pwned3","1"); //' node -e 'require("./out.js")' ``` **AMD vector:** ```bash node bin/handlebars templates -o out.js -a \ -h "'); require('fs').writeFileSync('pwned4','1'); // " node -e 'require("./out.js")' ``` ## Workarounds - **Validate all CLI inputs** before invoking the precompiler. Reject filenames and option values that contain characters with JavaScript string-escaping significance (`"`, `'`, `;`, etc.). - **Use a fixed, trusted namespace string** passed via a configuration file rather than command-line arguments in automated pipelines. - **Run the precompiler in a sandboxed environment** (container with no write access to sensitive paths) to limit the impact of successful exploitation. - **Audit template filenames** in any repository or package that is consumed by an automated build pipeline.

Source published

27 Mar 2026 18:22:10 UTC

Source modified

10 Sep 2026 03:50:41 UTC

Observed here

24 Oct 2026 13:17:17 UTC

Source terms

GitHub Advisory Database · CC-BY-4.0

Original source record · Cite this exact observation · Complete original publisher JSON

This view projects the publisher's source fields for reading; the original JSON retains additional fields and CVE enrichment containers. Attribution: osv · GitHub Advisory Database · CC-BY-4.0. Source text is retained; field grouping and change labels are provided by ChangeIntel.

CVSS_V3 · CVSS:3.1/AV:L/AC:L/PR:L/UI:R/S:C/C:H/I:H/A:H

Publisher rating · HIGH