How severe is GHSA-2cf5-4w76-r9qv?

GHSA-2cf5-4w76-r9qv has a CVSS score of 7.3/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by GHSA-2cf5-4w76-r9qv?

GHSA-2cf5-4w76-r9qv affects the following packages: handlebars (npm), handlebars (npm). Ecosystems affected: npm.

How do I fix GHSA-2cf5-4w76-r9qv?

Update handlebars to 3.0.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2cf5-4w76-r9qv is resolved across your whole dependency graph.

How do I detect GHSA-2cf5-4w76-r9qv in my npm dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for handlebars, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate GHSA-2cf5-4w76-r9qv if there is no patch (or I can't update yet)?

Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Is GHSA-2cf5-4w76-r9qv actively exploited in the wild?

No public exploit code has been indexed for GHSA-2cf5-4w76-r9qv yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

When was GHSA-2cf5-4w76-r9qv published, and has it been updated?

GHSA-2cf5-4w76-r9qv was published on September 4, 2020 and was last updated on September 10, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

📦

📦 npm

Not in CISA KEV

HIGH severity

Arbitrary Code Execution in handlebarsGHSA-2cf5-4w76-r9qv

HIGH

GHSA-2cf5-4w76-r9qv is a high-severity (CVSS 7.3) remote code execution vulnerability in handlebars. A fix is available for handlebars — see the affected versions and patch details below.

Published

Sep 4, 2020

Updated

Sep 10, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Sep 10, 2026 · OSV.dev, FIRST.org (EPSS)

Real-World Exposure

2 pkgs affected

How broadly this vulnerability is actually deployed: weekly install volume shows current usage, and reverse-dependency count shows how many other packages break if it stays unpatched.

17Kother npm packages depend on this — each one inherits the vulnerability until it's patched upstream

handlebarsnpm

50.6Mdownloads / week

Description

Versions of handlebars prior to 3.0.8 or 4.5.2 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting).

The following template can be used to demonstrate the vulnerability:

	{{#with split as |a|}}
		{{pop (push "alert('Vulnerable Handlebars JS');")}}
		{{#with (concat (lookup join (slice 0 1)))}}
			{{#each (slice 2 3)}}
				{{#with (apply 0 a)}}
					{{.}}
				{{/with}}
			{{/each}}
		{{/with}}
	{{/with}}
{{/with}}```


## Recommendation

Upgrade to version 3.0.8, 4.5.2 or later.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
📦npm	`handlebars`	all versions	3.0.8`npm install handlebars@3.0.8`
📦npm	`handlebars`	≥ 4.0.0&&< 4.5.2	4.5.2`npm install handlebars@4.5.2`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for handlebars, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update handlebars to 3.0.8 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-2cf5-4w76-r9qv is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.

Frequently Asked Questions

Versions of `handlebars` prior to 3.0.8 or 4.5.2 are vulnerable to Arbitrary Code Execution. The package's lookup helper fails to properly validate templates, allowing attackers to submit templates that execute arbitrary JavaScript in the system. It can be used to run arbitrary code in a server processing Handlebars templates or on a victim's browser (effectively serving as Cross-Site Scripting). The following template can be used to demonstrate the vulnerability: ```{{#with "constructor"}} {{#with split as |a|}} {{pop (push "alert('Vulnerable Handlebars JS');")}} {{#with (concat (look

O3 Security · Impact-Aware SCA

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