Vulnerability-Lookup

UBUNTU-CVE-2026-18036 (CVE-2026-18036)

Vulnerability from osv_ubuntu – Published: 2026-10-05 00:00 – Updated: 2026-10-05 00:00 – Source website

Details

In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation's division-free fold and select; the results are unchanged.

Severity

8.2 (High)


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

N/A (UNKNOWN)


                    
                      medium

References

URL

Type

	https://ubuntu.com/security/CVE-2026-18036	REPORT
	https://www.cve.org/CVERecord?id=CVE-2026-18036	REPORT
	https://github.com/bcgit/bc-java/wiki/CVE%E2%80%9…	REPORT
	https://github.com/bcgit/bc-java/commit/9c9ad88b6…	REPORT

JSON

To clipboard

{
  "affected": [
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.51-4ubuntu1+esm1"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.51-4ubuntu1+esm1"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.51-4ubuntu1+esm1"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.51-4ubuntu1+esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:16.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.51-4ubuntu1+esm1?arch=source\u0026distro=esm-apps/xenial"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.49+dfsg-3ubuntu1",
        "1.51-4ubuntu1",
        "1.51-4ubuntu1+esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.59-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.59-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.59-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.59-1ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:18.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.59-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/bionic"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.57-1",
        "1.58-1",
        "1.59-1",
        "1.59-1ubuntu0.1~esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.61-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.61-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.61-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.61-1ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:20.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.61-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/focal"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.61-1",
        "1.61-1ubuntu0.1~esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.68-5ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.68-5ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.68-5ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.68-5ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbctls-java",
            "binary_version": "1.68-5ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:22.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.68-5ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/jammy"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.68-2",
        "1.68-4",
        "1.68-5",
        "1.68-5ubuntu0.1~esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcjmail-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbctls-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          },
          {
            "binary_name": "libbcutil-java",
            "binary_version": "1.77-1ubuntu0.1~esm1"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:Pro:24.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.77-1ubuntu0.1~esm1?arch=source\u0026distro=esm-apps/noble"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.72-2",
        "1.77-1",
        "1.77-1ubuntu0.1~esm1"
      ]
    },
    {
      "ecosystem_specific": {
        "binaries": [
          {
            "binary_name": "libbcjmail-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbcmail-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbcpg-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbcpkix-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbcprov-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbctls-java",
            "binary_version": "1.80-3"
          },
          {
            "binary_name": "libbcutil-java",
            "binary_version": "1.80-3"
          }
        ]
      },
      "package": {
        "ecosystem": "Ubuntu:26.04:LTS",
        "name": "bouncycastle",
        "purl": "pkg:deb/ubuntu/bouncycastle@1.80-3?arch=source\u0026distro=resolute"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ],
      "versions": [
        "1.80-3"
      ]
    }
  ],
  "aliases": [],
  "details": "In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation\u0027s division-free fold and select; the results are unchanged.",
  "id": "UBUNTU-CVE-2026-18036",
  "modified": "2026-10-05T00:00:00Z",
  "published": "2026-10-05T00:00:00Z",
  "references": [
    {
      "type": "REPORT",
      "url": "https://ubuntu.com/security/CVE-2026-18036"
    },
    {
      "type": "REPORT",
      "url": "https://www.cve.org/CVERecord?id=CVE-2026-18036"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/bcgit/bc-java/wiki/CVE%E2%80%902026%E2%80%9018036"
    },
    {
      "type": "REPORT",
      "url": "https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"
    }
  ],
  "related": [],
  "schema_version": "1.7.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:H/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/U:Amber",
      "type": "CVSS_V4"
    },
    {
      "score": "medium",
      "type": "Ubuntu"
    }
  ],
  "upstream": [
    "CVE-2026-18036"
  ]
}

CVE-2026-18036 (GCVE-0-2026-18036)

Vulnerability from cvelistv5 – Published: 2026-10-02 07:54 – Updated: 2026-10-02 17:42

Title

NTRU leaks private key information by reducing secret values with a non-constant-time integer division

Summary

Severity

8.2 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-02 17:42 UTC

CWE

CWE-208 - Observable Timing Discrepancy

Assigner

bcorg mitre root Scorecard

References

2 references

URL	Tags
https://github.com/bcgit/bc-java/wiki/CVE%E2%80%9…	vendor-advisory
https://github.com/bcgit/bc-java/commit/9c9ad88b6…	patch

Impacted products

1 product

Vendor	Product	Version
Legion of the Bouncy Castle Inc.	BC-JAVA	Affected: 1.73 , < 1.86 (maven)

Credits

The Robusta team: Deepak Bhargavan Pillai, Anirban Chakraborty, Chitchanok Chuengsatiansup, Matthew Roughan, Peter Schwabe, and Yuval Yarom

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-18036",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-02T17:42:43.345821Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-02T17:42:56.393Z",
          "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": [
            "Polynomial",
            "NTRUSampling"
          ],
          "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, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation\u0027s division-free fold and select; the results are unchanged.\u003c/p\u003e"
            }
          ],
          "value": "In Bouncy Castle for Java before 1.86, NTRU reduced secret values with the % operator in three helpers whose reference implementations are deliberately division-free, so each reduction was carried out by an integer division whose latency depends on the secret operand. Polynomial.modQ divided by a variable divisor, which a compiler cannot strength-reduce to a multiply the way it can a constant one, so it emitted a division on every call including on the decapsulation path where the dividend derives from the private key; Polynomial.mod3 and NTRUSampling.mod3 divided the secret key polynomials f and g during key generation, the message polynomials r and m during encapsulation, and coefficients recovered during decapsulation. An attacker able to measure that timing can recover information about the NTRU private key. modQ now masks, which is exact because q is always a power of two, and mod3 uses the reference implementation\u0027s division-free fold and select; the results are unchanged."
        }
      ],
      "metrics": [
        {
          "cvssV4_0": {
            "Automatable": "NOT_DEFINED",
            "Recovery": "NOT_DEFINED",
            "Safety": "NOT_DEFINED",
            "attackComplexity": "HIGH",
            "attackRequirements": "PRESENT",
            "attackVector": "NETWORK",
            "baseScore": 8.2,
            "baseSeverity": "HIGH",
            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "AMBER",
            "subAvailabilityImpact": "NONE",
            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/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": "2026-10-02T07:54:16.063Z",
        "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%9018036"
        },
        {
          "tags": [
            "patch"
          ],
          "url": "https://github.com/bcgit/bc-java/commit/9c9ad88b6003bb6230d2434bd892cc1e95b294e4"
        }
      ],
      "source": {
        "discovery": "EXTERNAL"
      },
      "title": "NTRU leaks private key information by reducing secret values with a non-constant-time integer division",
      "x_generator": {
        "engine": "bc release-notes template"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "91579145-5d7b-4cc5-b925-a0262ff19630",
    "assignerShortName": "bcorg",
    "cveId": "CVE-2026-18036",
    "datePublished": "2026-10-02T07:54:16.063Z",
    "dateReserved": "2026-07-28T08:28:40.900Z",
    "dateUpdated": "2026-10-02T17:42:56.393Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

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

UBUNTU-CVE-2026-18036 (CVE-2026-18036)

CVE-2026-18036 (GCVE-0-2026-18036)

Tags

Sightings

Nomenclature

Related by attack behaviour