Vulnerability-Lookup

GHSA-6W4X-4WPP-M6R4

Vulnerability from github – Published: 2026-10-02 09:31 – Updated: 2026-10-02 09:31

Details

Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not.

Severity

8.2 (High)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-63567"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-203"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-02T07:16:37Z",
    "severity": "HIGH"
  },
  "details": "Observable discrepancy in IesEngine.DecryptBlock in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote attacker who has captured an IES or ECIES ciphertext, and who can submit modified ciphertexts for decryption under the same key pair, to recover its plaintext via a CBC padding-oracle attack, because in block-cipher mode the engine decrypts the ciphertext and removes its padding before verifying the MAC. A padding failure is therefore reported with a different error message, and without the MAC computation, compared with a MAC failure. Only applications that construct IesEngine directly with a padded block cipher, such as AES in CBC mode with PKCS#7 padding, are affected; stream-mode IES is not.",
  "id": "GHSA-6w4x-4wpp-m6r4",
  "modified": "2026-10-02T09:31:17Z",
  "published": "2026-10-02T09:31:17Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63567"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/commit/eaa42e1e8125b3e2e25e365c4194c7cd5932360b"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/commit/f881400b761134160ec2a05fd27c3e569453788d"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63567"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X",
      "type": "CVSS_V4"
    }
  ]
}

CVE-2026-63567 (GCVE-0-2026-63567)

Vulnerability from cvelistv5 – Published: 2026-10-02 06:58 – Updated: 2026-10-02 18:09

Title

IesEngine block-cipher mode checks padding before MAC (CBC padding oracle)

Summary

Severity

8.2 (High)


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

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-02 18:09 UTC

CWE

CWE-203 - Observable Discrepancy

Assigner

bcorg mitre root Scorecard

References

3 references

URL	Tags
https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63567	vendor-advisory
https://github.com/bcgit/bc-csharp/commit/f881400…	patch
https://github.com/bcgit/bc-csharp/commit/eaa42e1…	patch

Impacted products

1 product

Vendor	Product	Version
Legion of the Bouncy Castle Inc.	bc-csharp	Affected: 0 , < 2.7.0 (semver)

Credits

Discovered by Claude, Anthropic's AI assistant, and triaged by the Anthropic security team in collaboration with Anthropic Research.

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JSON

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    "adp": [
      {
        "metrics": [
          {
            "other": {
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                "id": "CVE-2026-63567",
                "options": [
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                    "Exploitation": "none"
                  },
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                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-02T18:09:42.725922Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
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        "providerMetadata": {
          "dateUpdated": "2026-10-02T18:09:54.933Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
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      }
    ],
    "cna": {
      "affected": [
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          "collectionURL": "https://www.nuget.org/packages/BouncyCastle.Cryptography",
          "defaultStatus": "unaffected",
          "packageName": "BouncyCastle.Cryptography",
          "product": "bc-csharp",
          "programFiles": [
            "crypto/src/crypto/engines/IesEngine.cs"
          ],
          "repo": "https://github.com/bcgit/bc-csharp",
          "vendor": "Legion of the Bouncy Castle Inc.",
          "versions": [
            {
              "lessThan": "2.7.0",
              "status": "affected",
              "version": "0",
              "versionType": "semver"
            }
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            "Recovery": "NOT_DEFINED",
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            "attackVector": "NETWORK",
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            "providerUrgency": "NOT_DEFINED",
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            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
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            "valueDensity": "NOT_DEFINED",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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          "scenarios": [
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      "references": [
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      "source": {
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      "title": "IesEngine block-cipher mode checks padding before MAC (CBC padding oracle)",
      "x_antReportIds": [
        "ANT-2026-J7SXX2NS",
        "ANT-2026-SNRMZ9MS"
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    "datePublished": "2026-10-02T06:58:32.487Z",
    "dateReserved": "2026-07-16T23:48:46.076Z",
    "dateUpdated": "2026-10-02T18:09:54.933Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2"
}

Sightings

Author	Source	Type	Date	Other

Nomenclature

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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.
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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.
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GHSA-6W4X-4WPP-M6R4

CVE-2026-63567 (GCVE-0-2026-63567)

Tags

Sightings

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