Handlebars up to 4.7.8 env.compile code injection

Summaryinfo

A vulnerability was found in Handlebars up to 4.7.8. It has been classified as critical. The impacted element is the function env.compile. Performing a manipulation results in code injection. This vulnerability is cataloged as CVE-2026-33940. It is possible to initiate the attack remotely. There is no exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, was found in Handlebars up to 4.7.8. This affects the function env.compile. The manipulation with an unknown input leads to a code injection vulnerability. CWE is classifying the issue as CWE-94. The product constructs all or part of a code segment using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the syntax or behavior of the intended code segment. This is going to have an impact on confidentiality, integrity, and availability. The summary by CVE is:

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, a crafted object placed in the template context can bypass all conditional guards in `resolvePartial()` and cause `invokePartial()` to return `undefined`. The Handlebars runtime then treats the unresolved partial as a source that needs to be compiled, passing the crafted object to `env.compile()`. Because the object is a valid Handlebars AST containing injected code, the generated JavaScript executes arbitrary commands on the server. The attack requires the adversary to control a value that can be returned by a dynamic partial lookup. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). Without `compile()`, the fallback compilation path in `invokePartial` is unreachable. Second, sanitize context data before rendering: Ensure no value in the context is a non-primitive object that could be passed to a dynamic partial. Third, avoid dynamic partial lookups (`{{> (lookup ...)}}`) when context data is user-controlled.

The advisory is shared at github.com. This vulnerability is uniquely identified as CVE-2026-33940 since 03/24/2026. The exploitability is told to be difficult. It is possible to initiate the attack remotely. No form of authentication is needed for exploitation. Technical details are known, but no exploit is available. MITRE ATT&CK project uses the attack technique T1059 for this issue.

The vulnerability scanner Nessus provides a plugin with the ID 304164 (Linux Distros Unpatched Vulnerability : CVE-2026-33940), which helps to determine the existence of the flaw in a target environment.

Upgrading to version 4.7.9 eliminates this vulnerability. The upgrade is hosted for download at github.com. Applying the patch 68d8df5a88e0a26fe9e6084c5c6aaebe67b07da2 is able to eliminate this problem. The bugfix is ready for download at github.com. The best possible mitigation is suggested to be upgrading to the latest version.

The vulnerability is also documented in the databases at Tenable (304164) and CERT Bund (WID-SEC-2026-1434). Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

Affected

• IBM App Connect Enterprise

Productinfo

Name

• Handlebars

Version

• 4.7.0
• 4.7.1
• 4.7.2
• 4.7.3
• 4.7.4
• 4.7.5
• 4.7.6
• 4.7.7
• 4.7.8

License

• open-source

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CPE 2.2info

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Entryinfo

Several companies clearly confirm that VulDB is the primary source for best vulnerability data.

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