GHSA-g9r4-xpmj-mj65
Prototype Pollution in handlebars
- Severity
- High
- The publisher's own rating, not a CVSS score
- Exploit chance (EPSS)
- —
- No score published
- Known exploited
- No
- Not in CISA's catalog
- Weakness
- CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
- Fix
3.0.8- Upgrade handlebars to this version or later
Description
Versions of handlebars prior to 3.0.8 or 4.5.3 are vulnerable to prototype pollution. It is possible to add or modify properties to the Object prototype through a malicious template. This may allow attackers to crash the application or execute Arbitrary Code in specific conditions.
Recommendation
Upgrade to version 3.0.8, 4.5.3 or later.
Affected versions
npm
| Package | Vulnerable | Fixed in |
|---|---|---|
| handlebars | < 3.0.8 |
3.0.8 |
| handlebars | >= 4.0.0, < 4.5.3 |
4.5.3 |
How to fix
Move to the fixed version or later with your package manager, update the lockfile, and run your tests. If the package only arrives through another dependency, upgrade that dependency first. If none of its releases pulls a fixed version yet, force the version with your package manager's override.
handlebars npm → 3.0.8
- npm
npm install handlebars@3.0.8- yarn
yarn add handlebars@3.0.8- pnpm
pnpm add handlebars@3.0.8
Weakness
CWE-1321: Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
The product receives input from an upstream component that specifies attributes that are to be initialized or updated in an object, but it does not properly control modifications of attributes of the object prototype.
How to prevent it
- Implementation: By freezing the object prototype first (for example, Object.freeze(Object.prototype)), modification of the prototype becomes impossible.
- Architecture and Design: By blocking modifications of attributes that resolve to object prototype, such as proto or prototype, this weakness can be mitigated.
- Implementation: When handling untrusted objects, validating using a schema can be used.
- Implementation: By using an object without prototypes (via Object.create(null) ), adding object prototype attributes by accessing the prototype via the special attributes becomes impossible, mitigating this weakness.
- Implementation: Map can be used instead of objects in most cases. If Map methods are used instead of object attributes, it is not possible to access the object prototype or modify it.
References
Other links
Timeline
- Published
- Last updated by the source
Related advisories
| Advisory | Severity | Why it's related |
|---|---|---|
| GHSA-8r5x-fm3f-whwj Handlebars: JavaScript Injection via AST Type Confusion in compile (bypass of CVE-2026-33937) | Critical | Also affects handlebars |
| GHSA-p8wg-vrv2-v86f Handlebars: JavaScript Injection via Own Property Check Bypass | Critical | Also affects handlebars |
| GHSA-xw65-4hp5-5hc7 Handlebars: JavaScript Injection via Unsafe Inline Embedding of Precompiled Templates | Medium | Also affects handlebars |
| GHSA-7rx3-28cr-v5wh Handlebars.js has a Prototype Method Access Control Gap via Missing __lookupSetter__ Blocklist Entry | Medium | Also affects handlebars |
| GHSA-442j-39wm-28r2 Handlebars.js has a Property Access Validation Bypass in container.lookup | Low | Also affects handlebars |
| GHSA-xjpj-3mr7-gcpf Handlebars.js has JavaScript Injection in CLI Precompiler via Unescaped Names and Options | High | Also affects handlebars |
| GHSA-xhpv-hc6g-r9c6 Handlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial | High | Also affects handlebars |
| GHSA-9cx6-37pm-9jff Handlebars.js has Denial of Service via Malformed Decorator Syntax in Template Compilation | High | Also affects handlebars |
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