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NVD / CVE Program· CNA GitHub_M

CVE-2026-33937: Handlebars.js has JavaScript Injection via AST Type Confusion

Noroxi assessment

Priority: Plan (action score 40/100)

  • Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
  • Probability of exploitation in the next 30 days: 1.9% (FIRST EPSS); higher than 79.7% of all records.
  • Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
  • According to CISA the attack is automatable: targets can be found by mass scanning.
  • Fixed version: node-handlebars (Debian:14) 3:4.7.9-1; handlebars (npm) 4.7.9.

Add it to your regular patch cycle. Upgrade to node-handlebars (Debian:14) 3:4.7.9-1; handlebars (npm) 4.7.9 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

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 to Remote Code Execution on the server. Version 4.7.9 fixes the issue. Some workarounds are available. Validate input type before calling `Handlebars.compile()`; ensure the argument is always a `string`, never a plain object or JSON-deserialized value. Use the Handlebars runtime-only build (`handlebars/runtime`) on the server if templates are pre-compiled at build time; `compile()` will be unavailable.

CriticalCVSS 9.8 · v3.1—Proof of concept Fix available
Published
Mar 27, 2026
Updated
Oct 26, 2026
EPSS
1.9% · 79th percentile

Report tools

JSON

Action score

40

Plan

Add it to your regular patch cycle.

CVSS
39 / 40 · 9.8 / 10
CISA KEV
0 / 30 · Not listed
EPSS
1 / 30 · 1.9%

CISA SSVC decision

Exploitation
proof of concept
Automatable
yes
Technical impact
total

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
—
CNA · GitHub_M
9.8
NVD has not scored this yet; the score shown is the CNA’s.

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Get told when this record changes

  • Not in KEV: no record of exploitation in the wild
  • Proof of concept exists, no weaponized module
  • A fix has been released

If any of these changes, we'll tell you in the daily email digest.

Follow CVE-2026-33937

When you'll hear from us

  • when it enters CISA KEV
  • when exploit code appears or is weaponized
  • when the record is updated (including a fixed version)
  • when EPSS rises 20 points in a week

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

VendorProduct
handlebarsjshandlebars

Is the Handlebars on your site affected?

The free JavaScript library scanner reads the Handlebars version from the files your site loads, matches this record and other known vulnerabilities, and gives the safe version on the same branch. If the version can't be read, it says so. No account needed.

Scan JavaScript libraries

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • handlebarsjs handlebars4.0.0 and later · before 4.7.9

Versions reported by the vendor

Affected version ranges reported by the assigning authority (GitHub_M). Independent of NVD's CPE analysis and usually ahead of it.

  • handlebars-lang handlebars.js

    • >= 4.0.0, < 4.7.9affected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12node-handlebarsfrom 0—
Debian:14node-handlebarsbefore 3:4.7.9-13:4.7.9-1
npmhandlebarsfrom 4.0.0 · before 4.7.94.7.9

Same product

handlebarsjs: all records

Other highest-scoring records for the same primary product.

  • CVE-2021-23369Remote Code Execution (RCE)
    41Plan
  • CVE-2021-23383The package handlebars before 4.7.7 are vulnerable to Prototype Pollution when selecting certain compiling options to compile templates comi
    40Plan
  • CVE-2019-20920Handlebars before 3.0.8 and 4.x before 4.5.3 is vulnerable to Arbitrary Code Execution.
    33Monitor

Published before and after this one in the same product

  • ← EarlierCVE-2019-20922Sep 30, 2020 · Handlebars before 4.4.5 allows Regular Expression Denial of Service (ReDoS) because of eager matching.
    31Monitor
  • ← EarlierCVE-2026-33916Mar 27, 2026 · Handlebars.js has Prototype Pollution Leading to XSS through Partial Template Injection
    18Monitor
  • Later →CVE-2026-33938Mar 27, 2026 · Handlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block
    32Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:node-handlebars3:4.7.9-1 · Debian:14Package registry (OSV)
npm:handlebars4.7.9Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×4

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:02026-03-28
Proof-of-concept repository on GitHubstars:32026-04-22
Proof-of-concept repository on GitHubstars:02026-07-30
Proof-of-concept repository on GitHubstars:12026-08-03

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoCsame day
  3. TodayNov 1, 2026+219 d

No history yet (it accumulates with the daily EPSS job).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-339380 days apartHandlebars.js has JavaScript Injection via AST Type Confusion by tampering @partial-block
    32Monitor
  • CVE-2026-339400 days apartHandlebars.js has JavaScript Injection via AST Type Confusion when passing an object as dynamic partial
    32Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
high · data or configuration can be modified
Availability
high · the service can be disrupted
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
High
Availability impact
High

Weakness class (CWE)

CWE-94 · Improper Control of Generation of Code ('Code Injection')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

nvd-secondary

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Show all references (6 more)

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records