Vulnerability-Lookup

GHSA-26WQ-P25C-J6FV

Vulnerability from github – Published: 2026-10-08 17:40 – Updated: 2026-10-08 17:40

Summary

msgpack5: Reserved byte can cause unbounded stream buffering

Details

Impact

The reserved MessagePack byte 0xc1 is incorrectly treated as incomplete input. When it appears at the start of a decoder stream, all subsequent data is retained while the decoder waits for bytes that can never make the value valid, allowing memory exhaustion.

Patches

The decoder now rejects 0xc1 as invalid input. Streaming decoders release buffered input and stop after unrecoverable decoding errors.

Workarounds

Reject 0xc1 before streaming input to msgpack5, and enforce stream byte and time limits.

Severity

5.9 (Medium)


                  
                    CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

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{
  "affected": [
    {
      "package": {
        "ecosystem": "npm",
        "name": "msgpack5"
      },
      "ranges": [
        {
          "events": [
            {
              "introduced": "0"
            },
            {
              "fixed": "6.1.0"
            }
          ],
          "type": "ECOSYSTEM"
        }
      ]
    }
  ],
  "aliases": [
    "CVE-2026-107299"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-228"
    ],
    "github_reviewed": true,
    "github_reviewed_at": "2026-10-08T17:40:01Z",
    "nvd_published_at": null,
    "severity": "MODERATE"
  },
  "details": "### Impact\n\nThe reserved MessagePack byte `0xc1` is incorrectly treated as incomplete input. When it appears at the start of a decoder stream, all subsequent data is retained while the decoder waits for bytes that can never make the value valid, allowing memory exhaustion.\n\n### Patches\n\nThe decoder now rejects `0xc1` as invalid input. Streaming decoders release buffered input and stop after unrecoverable decoding errors.\n\n### Workarounds\n\nReject `0xc1` before streaming input to msgpack5, and enforce stream byte and time limits.",
  "id": "GHSA-26wq-p25c-j6fv",
  "modified": "2026-10-08T17:40:01Z",
  "published": "2026-10-08T17:40:01Z",
  "references": [
    {
      "type": "WEB",
      "url": "https://github.com/mcollina/msgpack5/security/advisories/GHSA-26wq-p25c-j6fv"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mcollina/msgpack5/commit/85da345bf1acc18ca441741e5cf4aa0ed0d69314"
    },
    {
      "type": "PACKAGE",
      "url": "https://github.com/mcollina/msgpack5"
    },
    {
      "type": "WEB",
      "url": "https://github.com/mcollina/msgpack5/releases/tag/v6.1.0"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
      "type": "CVSS_V3"
    }
  ],
  "summary": "msgpack5: Reserved byte can cause unbounded stream buffering"
}

CVE-2026-107299 (GCVE-0-2026-107299)

Vulnerability from cvelistv5 – Published: 2026-10-08 17:09 – Updated: 2026-10-09 15:15

Title

msgpack5: Reserved byte can cause unbounded stream buffering

Summary

msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder treats the reserved MessagePack byte 0xc1 as incomplete input instead of invalid input. When 0xc1 begins a stream, subsequent data remains buffered while the decoder waits for bytes that cannot make the value valid, allowing a remote peer to exhaust memory. This issue is fixed in version 6.1.0.

Severity

5.9 (Medium)


                        
                          CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator · CISA-ADP (v2.0.3)

Decision recorded 2026-10-08 20:23 UTC

CWE

CWE-228 - Improper Handling of Syntactically Invalid Structure

Assigner

GitHub_M CNA under the mitre root

CNA scorecard C 72/100 over 7588 records in the last 180 days details

References

3 references

URL	Tags
https://github.com/mcollina/msgpack5/security/adv…	x_refsource_CONFIRM
https://github.com/mcollina/msgpack5/commit/85da3…	x_refsource_MISC
https://github.com/mcollina/msgpack5/releases/tag…	x_refsource_MISC

Impacted products

1 product

Vendor	Product	Version
mcollina	msgpack5	Affected: < 6.1.0

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JSON

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{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-107299",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-10-08T20:23:17.872522Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-10-09T15:15:00.980Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "msgpack5",
          "vendor": "mcollina",
          "versions": [
            {
              "status": "affected",
              "version": "\u003c 6.1.0"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "msgpack5 is a msgpack v5 implementation for node.js and the browser. Prior to 6.1.0, the streaming decoder treats the reserved MessagePack byte 0xc1 as incomplete input instead of invalid input. When 0xc1 begins a stream, subsequent data remains buffered while the decoder waits for bytes that cannot make the value valid, allowing a remote peer to exhaust memory. This issue is fixed in version 6.1.0."
        }
      ],
      "metrics": [
        {
          "cvssV3_1": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "HIGH",
            "baseScore": 5.9,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "NONE",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "NONE",
            "vectorString": "CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H",
            "version": "3.1"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-228",
              "description": "CWE-228: Improper Handling of Syntactically Invalid Structure",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-08T17:09:47.191Z",
        "orgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
        "shortName": "GitHub_M"
      },
      "references": [
        {
          "name": "https://github.com/mcollina/msgpack5/security/advisories/GHSA-26wq-p25c-j6fv",
          "tags": [
            "x_refsource_CONFIRM"
          ],
          "url": "https://github.com/mcollina/msgpack5/security/advisories/GHSA-26wq-p25c-j6fv"
        },
        {
          "name": "https://github.com/mcollina/msgpack5/commit/85da345bf1acc18ca441741e5cf4aa0ed0d69314",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/mcollina/msgpack5/commit/85da345bf1acc18ca441741e5cf4aa0ed0d69314"
        },
        {
          "name": "https://github.com/mcollina/msgpack5/releases/tag/v6.1.0",
          "tags": [
            "x_refsource_MISC"
          ],
          "url": "https://github.com/mcollina/msgpack5/releases/tag/v6.1.0"
        }
      ],
      "source": {
        "advisory": "GHSA-26wq-p25c-j6fv",
        "discovery": "UNKNOWN"
      },
      "title": "msgpack5: Reserved byte can cause unbounded stream buffering"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "a0819718-46f1-4df5-94e2-005712e83aaa",
    "assignerShortName": "GitHub_M",
    "cveId": "CVE-2026-107299",
    "datePublished": "2026-10-08T17:09:47.191Z",
    "dateReserved": "2026-10-07T15:53:23.587Z",
    "dateUpdated": "2026-10-09T15:15:00.980Z",
    "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.

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