Raw vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:HSummary
CVE-2026-33938 is a high-severity Code Injection (CWE-94) vulnerability in Handlebarsjs Handlebars. Its CVSS base score is 8.1 (High).
Operationally, exploitation aligns with the MITRE ATT&CK technique Command and Scripting Interpreter (T1059); ranked in the top 50% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog; a public proof-of-concept is referenced.
The strongest mitigations our analysis identified map to SA-11 (Developer Testing and Evaluation) and SI-10 (Information Input Validation) — see the control section below for these in your framework.
Deeper analysis AI-assisted summary
Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.
CVE-2026-33938 is a high-severity vulnerability (CVSS 3.1 score of 8.1) affecting Handlebars.js, a templating engine for building semantic templates, in versions 4.0.0 through 4.7.8. The issue stems from the `@partial-block` special variable being stored in the template data context, making it reachable and mutable from within a template via helpers that accept arbitrary objects. An attacker can overwrite `@partial-block` with a crafted Handlebars Abstract Syntax Tree (AST), and a subsequent invocation of `{{> @partial-block}}` will compile and execute that AST, resulting in arbitrary JavaScript code execution on the server. The vulnerability is associated with CWE-94 (improper control of code generation) and CWE-843 (access of resource using incompatible type).
Exploitation requires network access with no privileges or user interaction (AV:N/AC:H/PR:N/UI:N/S:U), but high attack complexity due to the need for untrusted input to influence templates or context data, combined with helpers that permit arbitrary writes to the context. Attackers can leverage this in scenarios where custom or third-party helpers (e.g., from packages like `handlebars-helpers`) process user-controlled data, enabling remote code execution with high impact on confidentiality, integrity, and availability.
The vulnerability is fixed in Handlebars version 4.7.9, as detailed in the project's security advisory (GHSA-3mfm-83xf-c92r) and release notes. Mitigation workarounds include using the runtime-only build (`require('handlebars/runtime')`), which lacks the vulnerable `compile()` method; auditing registered helpers to ensure they treat context data as read-only and do not write arbitrary values; and avoiding third-party helpers in environments with untrusted template or context input. Relevant patches and details are available in the fix commit and release tag on the Handlebars GitHub repository.
OWASP Top 10 for Web (2025)
EU & UK References
- 🇪🇺 ENISA EUVD: EUVD-2026-16849
Vulnerability Data
Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, the `@partial-block` special variable is stored in the template data context and is reachable and mutable from within a template via helpers that accept…
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arbitrary objects. When a helper overwrites `@partial-block` with a crafted Handlebars AST, a subsequent invocation of `{{> @partial-block}}` compiles and executes that AST, enabling arbitrary JavaScript execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. First, use the runtime-only build (`require('handlebars/runtime')`). The `compile()` method is absent, eliminating the vulnerable fallback path. Second, audit registered helpers for any that write arbitrary values to context objects. Helpers should treat context data as read-only. Third, avoid registering helpers from third-party packages (such as `handlebars-helpers`) in contexts where templates or context data can be influenced by untrusted input.
- CWE(s)
Related Threats
MITRE ATT&CK Enterprise Techniques
CVEs Like This One
Affected Assets
Mitigating Controls
Control response
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V1.5.2V3.2.3V15.3.5V1.1.2
Mitigating Controls (NIST 800-53 r5) AI
Developer testing and evaluation finds code paths that accept and execute externally influenced strings.
Input validation directly stops untrusted data from being used to construct executable code without neutralization.
Least privilege limits the damage an injected code fragment can perform once executed.
Requiring documented secure development standards and tools enforces use of safe code-generation APIs and escaping.
Engineering principles can require use of type-safe languages, static typing, and runtime type checks that structurally avoid allocating one type and accessing another.
Memory-protection controls limit the blast radius when a type-confusion access occurs but do not stop the flaw itself.
Mitigating Controls (NIST CSF 2.0) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→CSF cross-walk (authority under review) — links open the control.
PR.PS-06's SDLC practices directly target injection flaws via secure coding and testing (mostly), yet as a single broad outcome it leaves many code-generation specifics unaddressed (partial).
PR.DS-10 protects runtime data confidentiality/integrity but has no bearing on neutralizing externally influenced input during code generation, so neither direction shows any preventive effect.
Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI
Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.
Security testing in development can detect type-confusion vulnerabilities through fuzzing and static analysis.
Secure SDLC mandates type-safe design and review that can catch type-confusion flaws.
Application security requirements can specify strong typing and interface contracts that reduce type confusion.
Secure architecture principles promote type-safe languages and memory-safety mechanisms that mitigate type confusion.
Banning unapproved code samples and unauthenticated web services, combined with secure-coding standards and SAST, prevents the dynamic generation or inclusion of attacker-supplied code.
Controls that restrict unauthorized or malicious code from being introduced via external networks or removable media limit opportunities for an attacker to inject and execute arbitrary code.