{
  "affected": [
    {
      "package": {
        "ecosystem": "Go",
        "name": "github.com/tillitis/tkeyclient"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "1.3.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-32953"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-303"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-03-17T19:42:31Z",
    "nvd_published_at": "2026-03-20T05:16:14Z",
    "severity": "MODERATE"
  },
  "details": "## Impact\n\nSome specific (1 out of 256) User Supplied Secrets (USS) were not used,\nmaking the resulting Compound Device Identifier (CDI) the same as if no\nUSS was provided.\n\nAffected client applications: all client apps using the\n[tkeyclient](https://github.com/tillitis/tkeyclient) Go module.\n\n## Patches\n\nUpgrade to v1.3.0.\n\n**NOTE WELL**: For the affected end users upgrading an app containing\n`tkeyclient` to v1.3.0 means their key material will change. An end\nuser can get their old keys by not entering any USS. Please make sure\nto communicate this to end users.\n\n## Affected users\n\nThe steps required to assess whether your USS is vulnerable may vary\ndepending on the client application. The example below shows how to\nperform the check using `tkey-ssh-agent` and the known vulnerable USS\n`adl`.\n\n1. Insert the TKey into the client\n2. Run `tkey-ssh-agent -p --uss`\n3. When prompted for a User Supplied Secret, enter `adl`\n4. Note the public key and call it `pubkey-with-uss`\n5. Remove the TKey from the client\n6. Insert the TKey into the client again\n7. Run `tkey-ssh-agent -p`\n8. Note the public key and call it `pubkey-without-uss`\n\nExpected behavior:\n`pubkey-with-uss` and `pubkey-without-uss` should not be equal.\n\nObserved behavior:\n`pubkey-with-uss` and `pubkey-without-uss` are equal.\n\n## Workaround\n\nWe recommend everyone using `tkeyclient` to update to v1.3.0 and\nrelease new versions of the client apps using it.\n\nHowever, end users that are unable to upgrade to a new version of a client\napp, the recommendation is to change to an unaffected USS. Include\nspecific instructions for your client app.\n\n## Details\n\nWhen loading the device app an optional 32 bytes USS digest is also\nsent. The intention is to ask the end user to enter a USS of arbitrary\nlength, hash it, and then send a 32 bytes digest to TKey.\n\nHowever, there was a bug when sending the digest from the client. The\nindex in the outgoing buffer is wrong and overwrites the boolean\ndefining if the USS is used or not.\n\nThis means that if the USS digest begins with a 0, the rest of the\ndigest is not used at all. If it begins with something else, setting\nthe boolean to true, the USS is used.\n\nThe exported `LoadApp()` function calls an internal helper function\n`loadApp()` which contains this code:\n\n```go\n  if len(secretPhrase) == 0 {\n    tx[6] = 0\n  } else {\n    tx[6] = 1 // Note the 6 here\n    // Hash user\u0027s phrase as USS\n    uss := blake2s.Sum256(secretPhrase)\n    copy(tx[6:], uss[:]) // Note that 6 is used again\n  }\n```\n\nA side effect of this behavior is that only 31 bytes of the USS are\nused. This is not considered a security issue, but an option has been\nadded to enforce use of the full USS. See the release notes for\ndetails. To avoid forcing all users to roll their keys, this option is\ndisabled by default and must be explicitly enabled.\n\n### The fix\n\nThe fix focuses on solving the vulnerability only by: 1) use correct\nindex, 2) always use the last 31 bytes of the USS:\n\n```go\n  if len(secretPhrase) == 0 {\n    tx[6] = 0\n  } else {\n    tx[6] = 1\n    // Hash user\u0027s phrase as USS\n    uss := blake2s.Sum256(secretPhrase)\n    copy(tx[7:], uss[1:])\n  }\n```\n\nThis change means the key material of affected end users will change\ncompared to earlier versions of `tkeyclient`. They have the choice of:\n\n1. Not using a USS and keep their keys.\n2. Keep using their USS and use new generated keys.\n3. Use another USS and thus new keys.",
  "id": "GHSA-4w7r-3222-8h6v",
  "modified": "2026-03-20T21:22:09Z",
  "published": "2026-03-17T19:42:31Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/tillitis/tkeyclient/security/advisories/GHSA-4w7r-3222-8h6v"
    },
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-32953"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tillitis/tkeyclient/commit/4954dccf0287657edf8d405057e134cdff9c59e8"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/tillitis/tkeyclient"
    },
    {
      "type": "WEB",
      "url": "https://github.com/tillitis/tkeyclient/releases/tag/v1.3.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:P/AC:L/AT:N/PR:N/UI:N/VC:L/VI:L/VA:L/SC:H/SI:H/SA:H",
      "type": "CVSS_V4"
    }
  ],
  "summary": "Tillitis TKey Client has an Error in Protocol Implementation"
}