Vulnerability-Lookup

GHSA-C5M8-Q98X-42WX

Vulnerability from github – Published: 2026-10-28 18:32 – Updated: 2026-10-28 18:32

Details

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous.

The multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false.

Encoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

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JSON

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{
  "affected": [],
  "aliases": [
    "CVE-2026-116266"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-436"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-10-28T18:17:13Z",
    "severity": null
  },
  "details": "MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous.\n\nThe multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false.\n\nEncoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient\u0027s mail client shows it.",
  "id": "GHSA-c5m8-q98x-42wx",
  "modified": "2026-10-28T18:32:12Z",
  "published": "2026-10-28T18:32:12Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-116266"
    },
    {
      "type": "WEB",
      "url": "https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes"
    }
  ],
  "schema_version": "1.4.0",
  "severity": []
}

CVE-2026-116266 (GCVE-0-2026-116266)

Vulnerability from cvelistv5 – Published: 2026-10-28 17:32 – Updated: 2026-10-28 17:32

Title

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous

Summary

MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous. The multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false. Encoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient's mail client shows it.

Severity

No CVSS data available.

CWE

CWE-436 - Interpretation Conflict

Assigner

CPANSec CNA under the redhat root

CNA scorecard C 63/100 over 317 records in the last 180 days details

References

1 reference

URL	Tags
https://metacpan.org/release/DSKOLL/MIME-tools-5.…	release-notes

Impacted products

1 product

Vendor	Product	Version
		Affected: 5.518 , < 5.521 (custom)

Show details on NVD website

JSON

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{
  "containers": {
    "cna": {
      "affected": [
        {
          "collectionURL": "https://cpan.org/modules",
          "defaultStatus": "unaffected",
          "modules": [
            "MIME::Head"
          ],
          "packageName": "MIME-tools",
          "packageURL": "pkg:cpan/MIME-tools",
          "programFiles": [
            "lib/MIME/Head.pm",
            "lib/MIME/Field/ParamVal.pm"
          ],
          "programRoutines": [
            {
              "name": "MIME::Head::multipart_boundary"
            },
            {
              "name": "MIME::Field::ParamVal::parse_params"
            }
          ],
          "repo": "https://salsa.debian.org/dskoll/mime-tools",
          "versions": [
            {
              "lessThan": "5.521",
              "status": "affected",
              "version": "5.518",
              "versionType": "custom"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous.\n\nThe multipart_boundary() method decodes RFC 2047 encoded words anywhere in the boundary, but the ambiguity check only fires when the whole value is one encoded word. A boundary such as abc=?us-ascii?Q?def?= is used as abcdef, and ambiguous_content() returns false.\n\nEncoded words are not allowed in parameters, so other mail readers split the message on the literal value. A remote sender can hide an attachment from a filter that relies on ambiguous_content() while the recipient\u0027s mail client shows it."
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-436",
              "description": "CWE-436 Interpretation Conflict",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-10-28T17:32:28.565Z",
        "orgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
        "shortName": "CPANSec"
      },
      "references": [
        {
          "tags": [
            "release-notes"
          ],
          "url": "https://metacpan.org/release/DSKOLL/MIME-tools-5.521/changes"
        }
      ],
      "solutions": [
        {
          "lang": "en",
          "value": "Upgrade to MIME-tools 5.521 or later."
        }
      ],
      "source": {
        "discovery": "UNKNOWN"
      },
      "title": "MIME::Head versions from 5.518 before 5.521 for Perl decode a partly encoded multipart boundary without flagging the parse as ambiguous",
      "x_generator": {
        "engine": "cpansec-cna-tool 0.1"
      }
    }
  },
  "cveMetadata": {
    "assignerOrgId": "9b29abf9-4ab0-4765-b253-1875cd9b441e",
    "assignerShortName": "CPANSec",
    "cveId": "CVE-2026-116266",
    "datePublished": "2026-10-28T17:32:28.565Z",
    "dateReserved": "2026-10-25T18:05:02.235Z",
    "dateUpdated": "2026-10-28T17:32:28.565Z",
    "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.
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.

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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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