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Vulnerability details: VCID-yv4k-1q7a-wqee
Vulnerability ID VCID-yv4k-1q7a-wqee
Aliases GHSA-7rx3-28cr-v5wh
Summary Handlebars.js has a Prototype Method Access Control Gap via Missing __lookupSetter__ Blocklist Entry ## Summary The prototype method blocklist in `lib/handlebars/internal/proto-access.js` blocks `constructor`, `__defineGetter__`, `__defineSetter__`, and `__lookupGetter__`, but omits the symmetric `__lookupSetter__`. This omission is only exploitable when the non-default runtime option `allowProtoMethodsByDefault: true` is explicitly set — in that configuration `__lookupSetter__` becomes accessible while its counterparts remain blocked, creating an inconsistent security boundary. `4.6.0` is the version that introduced `protoAccessControl` and the `allowProtoMethodsByDefault` runtime option. ## Description In `lib/handlebars/internal/proto-access.js`: ```javascript const methodWhiteList = Object.create(null); methodWhiteList['constructor'] = false; methodWhiteList['__defineGetter__'] = false; methodWhiteList['__defineSetter__'] = false; methodWhiteList['__lookupGetter__'] = false; // __lookupSetter__ intentionally blocked in CVE-2021-23383, // but omitted here — creating an asymmetric blocklist ``` All four legacy accessor helpers (`__defineGetter__`, `__defineSetter__`, `__lookupGetter__`, `__lookupSetter__`) were involved in the exploit chain addressed by CVE-2021-23383. Three of the four were explicitly blocked; `__lookupSetter__` was left out. When `allowProtoMethodsByDefault: true` is set, any prototype method **not present** in `methodWhiteList` is permitted by default. Because `__lookupSetter__` is absent from the list, it passes the `checkWhiteList` check and is accessible in templates, while `__lookupGetter__` (its sibling) is correctly denied. ## Workarounds - Do **not** set `allowProtoMethodsByDefault: true`. The default configuration is not affected. - If `allowProtoMethodsByDefault` must be enabled, ensure templates do not reference `__lookupSetter__` through untrusted input.
Status Published
Exploitability None
Weighted Severity None
Risk None
Affected and Fixed Packages Package Details
Weaknesses (3)
CWE-1321 Improperly Controlled Modification of Object Prototype Attributes ('Prototype Pollution')
CWE-937 OWASP Top Ten 2013 Category A9 - Using Components with Known Vulnerabilities
CWE-1035 OWASP Top Ten 2017 Category A9 - Using Components with Known Vulnerabilities
System Score Found at
cvssv3.1 4.8 https://github.com/advisories/GHSA-765h-qjxv-5f44
generic_textual MODERATE https://github.com/advisories/GHSA-765h-qjxv-5f44
cvssv3.1 4.8 https://github.com/handlebars-lang/handlebars.js
generic_textual MODERATE https://github.com/handlebars-lang/handlebars.js
cvssv3.1 4.8 https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
generic_textual MODERATE https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
cvssv3.1 4.8 https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-7rx3-28cr-v5wh
generic_textual MODERATE https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-7rx3-28cr-v5wh
Reference id Reference type URL
https://github.com/handlebars-lang/handlebars.js
https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-7rx3-28cr-v5wh
GHSA-765h-qjxv-5f44 https://github.com/advisories/GHSA-765h-qjxv-5f44
GHSA-7rx3-28cr-v5wh https://github.com/advisories/GHSA-7rx3-28cr-v5wh
No exploits are available.
Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/advisories/GHSA-765h-qjxv-5f44
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

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Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/handlebars-lang/handlebars.js
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

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Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.9
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

local

physical

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Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:N Found at https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-7rx3-28cr-v5wh
Attack Vector (AV) Attack Complexity (AC) Privileges Required (PR) User Interaction (UI) Scope (S) Confidentiality Impact (C) Integrity Impact (I) Availability Impact (A)

network

adjacent_network

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physical

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No EPSS data available for this vulnerability.

Date Actor Action Source VulnerableCode Version
2026-06-04T16:58:35.014488+00:00 GithubOSV Importer Import https://github.com/github/advisory-database/blob/main/advisories/github-reviewed/2026/03/GHSA-7rx3-28cr-v5wh/GHSA-7rx3-28cr-v5wh.json 38.6.0