CVE-2026-33937: Handlebars provides the power necessary to let users build semantic templates

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CRITICAL 9.8REMOTEUPGRADE

CVE-2026-33937 is a critical-severity flaw (CVSS 9.8) affecting handlebars. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string. The `value` field of a `NumberLiteral` AST node is emitted directly into the generated JavaScript without quoting or sanitization. An attacker who can supply a crafted AST to `compile()` can therefore inject and execute arbitrary JavaScript, leading

Why this priority

Critical severity
Public exploit reference
CISA SSVC: automatable with total technical impact
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	9.8 (Critical)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	1.9% (top 20%)
CISA exploited list	No
Weakness	CWE-94, CWE-843
Published	2026-03-27
Last modified	2026-10-26

Publisher (CNA): GitHub, Inc. · Vendor: handlebarsjs

Last updated 2026-10-26 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-03-27 21:17 UTCPublished CVE record published
2026-10-26 22:10 UTCUpdated Record last modified

handlebarsjs handlebars UPGRADE

Affected: >= 4.0.0 and < 4.7.9

Fixed in: 4.7.9

Safe to downgrade to: a release before 4.0.0

1. Check installed version

npm ls handlebars

2. UPGRADE to 4.7.9

npm install handlebars@">=4.7.9"

3. If no update is available yet, DOWNGRADE to a release before 4.0.0

npm view handlebars versions npm install handlebars@"<4.0.0"

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Exact fixes by distribution

npm · handlebars · FIXED · 4.7.9 · vulnerable: >= 4.0.0, <= 4.7.8 · source

npm install handlebars@">=4.7.9" npm ls handlebars

Debian 12 · node-handlebars · NO FIX YET

Debian 13 · node-handlebars · NO FIX YET

RHEL 10 · firefox · NOT AFFECTED

RHEL 10 · thunderbird · NO FIX YET

RHEL 7 · firefox · NOT AFFECTED

RHEL 8 · 389-ds:1.4/389-ds-base · DEFERRED

RHEL 8 · firefox · NOT AFFECTED

Public exploits and detection

Public code exists for this CVE. Treat unpatched systems as at risk, and only run PoCs in a lab.

GitHub PoC: EQSTLab/CVE-2026-33937 (3 stars)
GitHub PoC: c0gnit00/CVE-2026-33937 (1 stars)
GitHub PoC: dinhvaren/cve-2026-33937 (0 stars)
Write-up: github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-2w6w-674q-4c4q

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-33937?

handlebars: upgrade to 4.7.9. Exact commands for each OS are on this page.

Is CVE-2026-33937 being exploited?

CVE-2026-33937 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-33937 affect?

CVE-2026-33937 affects handlebars. Severity is critical (CVSS 9.8). Handlebars provides the power necessary to let users build semantic templates. In versions 4.0.0 through 4.7.8, `Handlebars.compile()` accepts a pre-parsed AST object in addition to a template string. The `value` field of a `NumberLiteral`

How urgent is CVE-2026-33937?

Priority 67/100. Critical severity; Public exploit reference; CISA SSVC: automatable with total technical impact; Remotely exploitable, no login, no user action

Related CVEs

CVE-2026-33938 HIGH 8.1 UPGRADE Handlebars provides the power necessary to let users build semantic templates
CVE-2026-33940 HIGH 8.1 UPGRADE Handlebars provides the power necessary to let users build semantic templates
CVE-2026-33939 HIGH 7.5 UPGRADE Handlebars provides the power necessary to let users build semantic templates
CVE-2026-33941 HIGH 8.2 UPGRADE Handlebars provides the power necessary to let users build semantic templates
CVE-2026-33916 MEDIUM 4.7 UPGRADE Handlebars provides the power necessary to let users build semantic templates

References

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