CVE-2026-18040 (GCVE-0-2026-18040)
Vulnerability from cvelistv5
Published
2026-10-03 08:55
Modified
2026-10-05 16:00
CWE
  • CWE-208 - Observable Timing Discrepancy
Summary
In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.
Impacted products
Show details on NVD website


{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-18040",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-05T16:00:03.782416Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-05T16:00:20.062Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "collectionURL": "https://www.bouncycastle.org/download/bouncy-castle-java/",
          "defaultStatus": "unaffected",
          "modules": [
            "core"
          ],
          "packageName": "bcprov",
          "packageURL": "pkg:maven/org.bouncycastle/bcprov-jdk18on",
          "platforms": [
            "all"
          ],
          "product": "BC-JAVA",
          "programFiles": [
            "GF",
            "HQCEngine",
            "ReedSolomon",
            "FastFourierTransform"
          ],
          "repo": "https://github.com/bcgit/bc-java",
          "vendor": "Legion of the Bouncy Castle Inc.",
          "versions": [
            {
              "lessThan": "1.86",
              "status": "affected",
              "version": "1.73",
              "versionType": "maven"
            }
          ]
        }
      ],
      "credits": [
        {
          "lang": "en",
          "type": "reporter",
          "value": "The Robusta team: Deepak Bhargavan Pillai, Anirban Chakraborty, Chitchanok Chuengsatiansup, Matthew Roughan, Peter Schwabe, and Yuval Yarom"
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "supportingMedia": [
            {
              "base64": false,
              "type": "text/html",
              "value": "\u003cp\u003eIn Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.\u003c/p\u003e"
            }
          ],
          "value": "In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "HIGH",
            "attackRequirements": "PRESENT",
            "attackVector": "LOCAL",
            "baseScore": 5.9,
            "baseSeverity": "MEDIUM",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "AMBER",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber",
            "version": "4.0",
            "vulnAvailabilityImpact": "NONE",
            "vulnConfidentialityImpact": "HIGH",
            "vulnIntegrityImpact": "NONE",
            "vulnerabilityResponseEffort": "NOT_DEFINED"
          },
          "format": "CVSS",
          "scenarios": [
            {
              "lang": "en",
              "value": "GENERAL"
            }
          ]
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-208",
              "description": "CWE-208 Observable Timing Discrepancy",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-03T08:55:06.766Z",
        "orgId": "91579145-5d7b-4cc5-b925-a0262ff19630",
        "shortName": "bcorg"
      },
      "references": [
        {
          "tags": [
            "vendor-advisory"
          ],
          "url": "https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018040"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/bcgit/bc-java/commit/283acd81048ec9e951032525279d3b58aaf0bb03"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "HQC leaks private key information through secret-indexed GF(2^8) tables and a secret-dependent fixed-weight sampler",
      "x_generator": {
        "engine": "bc release-notes template"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "91579145-5d7b-4cc5-b925-a0262ff19630",
    "assignerShortName": "bcorg",
    "cveId": "CVE-2026-18040",
    "datePublished": "2026-10-03T08:55:06.766Z",
    "dateReserved": "2026-07-28T08:50:28.760Z",
    "dateUpdated": "2026-10-05T16:00:20.062Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "vulnrichment": {
      "containers": "{\"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-18040\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-10-05T16:00:03.782416Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-10-05T16:00:13.080Z\"}}], \"cna\": {\"title\": \"HQC leaks private key information through secret-indexed GF(2^8) tables and a secret-dependent fixed-weight sampler\", \"source\": {\"discovery\": \"EXTERNAL\"}, \"credits\": [{\"lang\": \"en\", \"type\": \"reporter\", \"value\": \"The Robusta team: Deepak Bhargavan Pillai, Anirban Chakraborty, Chitchanok Chuengsatiansup, Matthew Roughan, Peter Schwabe, and Yuval Yarom\"}], \"metrics\": [{\"format\": \"CVSS\", \"cvssV4_0\": {\"Safety\": \"NOT_DEFINED\", \"version\": \"4.0\", \"Recovery\": \"NOT_DEFINED\", \"baseScore\": 5.9, \"Automatable\": \"NOT_DEFINED\", \"attackVector\": \"LOCAL\", \"baseSeverity\": \"MEDIUM\", \"valueDensity\": \"NOT_DEFINED\", \"vectorString\": \"CVSS:4.0/AV:L/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber\", \"exploitMaturity\": \"NOT_DEFINED\", \"providerUrgency\": \"AMBER\", \"userInteraction\": \"NONE\", \"attackComplexity\": \"HIGH\", \"attackRequirements\": \"PRESENT\", \"privilegesRequired\": \"NONE\", \"subIntegrityImpact\": \"NONE\", \"vulnIntegrityImpact\": \"NONE\", \"subAvailabilityImpact\": \"NONE\", \"vulnAvailabilityImpact\": \"NONE\", \"subConfidentialityImpact\": \"NONE\", \"vulnConfidentialityImpact\": \"HIGH\", \"vulnerabilityResponseEffort\": \"NOT_DEFINED\"}, \"scenarios\": [{\"lang\": \"en\", \"value\": \"GENERAL\"}]}], \"affected\": [{\"repo\": \"https://github.com/bcgit/bc-java\", \"vendor\": \"Legion of the Bouncy Castle Inc.\", \"modules\": [\"core\"], \"product\": \"BC-JAVA\", \"versions\": [{\"status\": \"affected\", \"version\": \"1.73\", \"lessThan\": \"1.86\", \"versionType\": \"maven\"}], \"platforms\": [\"all\"], \"packageURL\": \"pkg:maven/org.bouncycastle/bcprov-jdk18on\", \"packageName\": \"bcprov\", \"programFiles\": [\"GF\", \"HQCEngine\", \"ReedSolomon\", \"FastFourierTransform\"], \"collectionURL\": \"https://www.bouncycastle.org/download/bouncy-castle-java/\", \"defaultStatus\": \"unaffected\"}], \"references\": [{\"url\": \"https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018040\", \"tags\": [\"vendor-advisory\"]}, {\"url\": \"https://github.com/bcgit/bc-java/commit/283acd81048ec9e951032525279d3b58aaf0bb03\", \"tags\": [\"patch\"]}], \"x_generator\": {\"engine\": \"bc release-notes template\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.\", \"supportingMedia\": [{\"type\": \"text/html\", \"value\": \"\u003cp\u003eIn Bouncy Castle for Java before 1.86, HQC leaked secret-derived data through two side channels: its GF(2^8) arithmetic used lookup tables indexed by field elements, making the cache line touched a function of the operand, and its fixed-weight support sampler left its duplicate scan as soon as a collision was found and stored accepted positions at a secret index. Both run on secret inputs during encapsulation and decapsulation, and the sampler re-expands the secret key from its seed on every decapsulation, so an attacker able to observe cache behaviour or decapsulation timing can recover information about the HQC private key. The field arithmetic is now table-free and the sampler branch-free within a batch of candidates, with output and randomness consumption unchanged.\u003c/p\u003e\", \"base64\": false}]}], \"problemTypes\": [{\"descriptions\": [{\"lang\": \"en\", \"type\": \"CWE\", \"cweId\": \"CWE-208\", \"description\": \"CWE-208 Observable Timing Discrepancy\"}]}], \"providerMetadata\": {\"orgId\": \"91579145-5d7b-4cc5-b925-a0262ff19630\", \"shortName\": \"bcorg\", \"dateUpdated\": \"2026-10-03T08:55:06.766Z\"}}}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-18040\", \"state\": \"PUBLISHED\", \"dateUpdated\": \"2026-10-05T16:00:20.062Z\", \"dateReserved\": \"2026-07-28T08:50:28.760Z\", \"assignerOrgId\": \"91579145-5d7b-4cc5-b925-a0262ff19630\", \"datePublished\": \"2026-10-03T08:55:06.766Z\", \"assignerShortName\": \"bcorg\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}


Log in or create an account to share your comment.




Tags
Taxonomy of the tags.


Loading…

Loading…

Loading…

Sightings

Author Source Type Date

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or seen somewhere by the user.
  • Confirmed: The vulnerability is confirmed from an analyst perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
  • Exploited: This vulnerability was exploited and seen by the user reporting the sighting.
  • Patched: This vulnerability was successfully patched by the user reporting the sighting.
  • Not exploited: This vulnerability was not exploited or seen by the user reporting the sighting.
  • Not confirmed: The user expresses doubt about the veracity of the vulnerability.
  • Not patched: This vulnerability was not successfully patched by the user reporting the sighting.


Loading…

Loading…