Vulnerability-Lookup

GHSA-496X-2F25-59FJ

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

Details

Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated DTLS peer to cause a denial of service through memory exhaustion via crafted handshake message fragments, because the reassembly buffer for each incoming handshake message was allocated at the 24-bit length declared in the fragment header, without the check against the peer's maximum handshake message size that TLS already applied. A fragment carrying no payload can force an allocation of almost 16 MB, for each of up to 16 pending messages per handshake, before the handshake is authenticated. DTLS servers and DTLS clients are both affected; TLS is not.

Severity

8.7 (High)


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

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{
  "affected": [],
  "aliases": [
    "CVE-2026-63566"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-789"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-02T07:16:36Z",
    "severity": "HIGH"
  },
  "details": "Memory allocation with excessive size value in the DTLS handshake reassembly (DtlsReliableHandshake, DtlsReassembler) in Legion of the Bouncy Castle Inc. bc-csharp before 2.7.0 allows a remote unauthenticated DTLS peer to cause a denial of service through memory exhaustion via crafted handshake message fragments, because the reassembly buffer for each incoming handshake message was allocated at the 24-bit length declared in the fragment header, without the check against the peer\u0027s maximum handshake message size that TLS already applied. A fragment carrying no payload can force an allocation of almost 16 MB, for each of up to 16 pending messages per handshake, before the handshake is authenticated. DTLS servers and DTLS clients are both affected; TLS is not.",
  "id": "GHSA-496x-2f25-59fj",
  "modified": "2026-10-02T09:31:17Z",
  "published": "2026-10-02T09:31:17Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-63566"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/commit/212d06474166d5e85be72c2dd4898313aa5dd5f3"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/commit/99afef612458f70f28e7824a09719bfc3a169bda"
    },
    {
      "type": "WEB",
      "url": "https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63566"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/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-2026-63566 (GCVE-0-2026-63566)

Vulnerability from cvelistv5 – Published: 2026-10-02 06:57 – Updated: 2026-10-02 18:08

Title

DTLS handshake reassembler allocates buffer from unchecked 24-bit length

Summary

Severity

8.7 (High)


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

SSVC

Exploitation: none Automatable: yes Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-02 18:07 UTC

CWE

CWE-789 - Memory Allocation with Excessive Size Value

Assigner

bcorg mitre root Scorecard

References

3 references

URL	Tags
https://github.com/bcgit/bc-csharp/wiki/CVE-2026-63566	vendor-advisory
https://github.com/bcgit/bc-csharp/commit/212d064…	patch
https://github.com/bcgit/bc-csharp/commit/99afef6…	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.

Show details on NVD website

JSON

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      {
        "metrics": [
          {
            "other": {
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                "id": "CVE-2026-63566",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "yes"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-02T18:07:25.493590Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-02T18:08:57.485Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
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          "collectionURL": "https://www.nuget.org/packages/BouncyCastle.Cryptography",
          "defaultStatus": "unaffected",
          "packageName": "BouncyCastle.Cryptography",
          "product": "bc-csharp",
          "programFiles": [
            "crypto/src/tls/DtlsReliableHandshake.cs",
            "crypto/src/tls/DtlsReassembler.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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      ],
      "credits": [
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      "metrics": [
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            "Recovery": "NOT_DEFINED",
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            "exploitMaturity": "NOT_DEFINED",
            "privilegesRequired": "NONE",
            "providerUrgency": "NOT_DEFINED",
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            "subConfidentialityImpact": "NONE",
            "subIntegrityImpact": "NONE",
            "userInteraction": "NONE",
            "valueDensity": "NOT_DEFINED",
            "vectorString": "CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N",
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            "vulnerabilityResponseEffort": "NOT_DEFINED"
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          "format": "CVSS",
          "scenarios": [
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      "references": [
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          "tags": [
            "patch"
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      "source": {
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      "title": "DTLS handshake reassembler allocates buffer from unchecked 24-bit length",
      "x_antReportIds": [
        "ANT-2026-67TQHZ95",
        "ANT-2026-EWREHKZ5"
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    "assignerShortName": "bcorg",
    "cveId": "CVE-2026-63566",
    "datePublished": "2026-10-02T06:57:21.718Z",
    "dateReserved": "2026-07-16T23:48:46.075Z",
    "dateUpdated": "2026-10-02T18:08:57.485Z",
    "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.

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GHSA-496X-2F25-59FJ

CVE-2026-63566 (GCVE-0-2026-63566)

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