# CVE-2026-33939: Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation > Attackers can crash Node.js applications by supplying templates with malformed decorator syntax, causing an unhandled TypeError during compilation. - **Severity:** High 7.5 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H`) - **Exploited in the wild:** Not known - **Login needed:** Not needed - **Attackable:** Over the internet - **Victim action needed:** Not needed - **Fix available:** Yes - **Published:** 27 Mar 2026 - **Updated:** 4 Sep 2026 - **Also known as:** CLEANSTART-2026-JZ33423, CLEANSTART-2026-YO10703, DEBIAN-CVE-2026-33939, GHSA-9cx6-37pm-9jff, MINI-4gh3-6qch-78xm, MINI-5gv5-223m-qmx4, MINI-626h-fcp8-gx78, MINI-8mqq-23v7-qq8m, MINI-9wmc-hx6q-73g7, MINI-f5fg-97q3-hmf7, MINI-hc2j-j87m-9f4h, MINI-hq9r-8wj2-8whr, MINI-pqxg-v2w6-xhr7, MINI-r26x-4v53-cw6g, MINI-rc4v-pjj8-hc9c, MINI-vg9x-cg67-hhq5, MINI-wxcq-fcr6-chqx, MINI-x97r-7ffq-vqfh, ROOT-APP-NPM-CVE-2026-33939, UBUNTU-CVE-2026-33939 ## What is CVE-2026-33939? CVE-2026-33939 is a high-severity denial of service vulnerability in handlebars-lang handlebars.js, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. ### Official description Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, when a Handlebars template contains decorator syntax referencing an unregistered decorator (e.g. `{{*n}}`), the compiled template calls `lookupProperty(decorators, "n")`, which returns `undefined`. The runtime then immediately invokes the result as a function, causing an unhandled `TypeError: ... is not a function` that crashes the Node.js process. Any application that compiles user-supplied templates without wrapping the call in a `try/catch` is vulnerable to a single-request Denial of Service. Version 4.7.9 fixes the issue. Some workarounds are available. Wrap compilation and rendering in `try/catch`. Validate template input before passing it to `compile()`; reject templates containing decorator syntax (`{{*...}}`) if decorators are not used in your application. Use the pre-compilation workflow; compile templates at build time and serve only pre-compiled templates; do not call `compile()` at request time. Weakness: CWE-248 (Uncaught Exception), CWE-754 (Improper Check for Unusual or Exceptional Conditions) ## Which versions are affected by CVE-2026-33939? 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-2026-33939? Upgrade handlebars to 4.7.9 or later. ## Is CVE-2026-33939 being exploited? It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33939 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-2026-33941](https://insights.sbomify.com/CVE-2026-33941/): Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options (high 8.3) - [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) ## Fix prompt for AI coding agents ```text Check this codebase for CVE-2026-33939 and fix it if it is affected. What it is: CVE-2026-33939 is a high-severity denial of service vulnerability in handlebars-lang handlebars.js, published on 27 Mar 2026. An attacker can exploit it over the internet without logging in, with no action from the victim. Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-33939 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-2026-33939/ (Markdown: https://insights.sbomify.com/CVE-2026-33939/index.md) ``` ## Sources - CVE record: https://www.cve.org/CVERecord?id=CVE-2026-33939 - NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-33939 - OSV: https://osv.dev/vulnerability/CVE-2026-33939 --- From sbomify Insights: https://insights.sbomify.com/CVE-2026-33939/ Summaries are generated and may contain mistakes; the official description above is the record.