Vulnerability-Lookup

CVE-2026-12259 (GCVE-0-2026-12259)

Vulnerability from cvelistv5 – Published: 2026-08-03 07:09 – Updated: 2026-08-03 14:59

Title

Improper Input Validation in nltk/nltk

Summary

In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.

Severity

5.3 (Medium)


                        
                          CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

SSVC

Exploitation: none Automatable: no Technical Impact: partial

CISA Coordinator (v2.0.3)

CWE

CWE-494 - Download of Code Without Integrity Check

Assigner

@huntr_ai

References

1 reference

URL	Tags
https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c…

Impacted products

1 product

Vendor	Product	Version
nltk	nltk/nltk	Affected: unspecified , ≤ latest (custom)

Show details on NVD website

JSON

To clipboard

{
  "containers": {
    "adp": [
      {
        "metrics": [
          {
            "other": {
              "content": {
                "id": "CVE-2026-12259",
                "options": [
                  {
                    "Exploitation": "none"
                  },
                  {
                    "Automatable": "no"
                  },
                  {
                    "Technical Impact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-03T14:55:19.698104Z",
                "version": "2.0.3"
              },
              "type": "ssvc"
            }
          }
        ],
        "providerMetadata": {
          "dateUpdated": "2026-08-03T14:59:01.815Z",
          "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
          "shortName": "CISA-ADP"
        },
        "title": "CISA ADP Vulnrichment"
      }
    ],
    "cna": {
      "affected": [
        {
          "product": "nltk/nltk",
          "vendor": "nltk",
          "versions": [
            {
              "lessThanOrEqual": "latest",
              "status": "affected",
              "version": "unspecified",
              "versionType": "custom"
            }
          ]
        }
      ],
      "descriptions": [
        {
          "lang": "en",
          "value": "In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications."
        }
      ],
      "metrics": [
        {
          "cvssV3_0": {
            "attackComplexity": "HIGH",
            "attackVector": "NETWORK",
            "availabilityImpact": "NONE",
            "baseScore": 5.3,
            "baseSeverity": "MEDIUM",
            "confidentialityImpact": "NONE",
            "integrityImpact": "HIGH",
            "privilegesRequired": "NONE",
            "scope": "UNCHANGED",
            "userInteraction": "REQUIRED",
            "vectorString": "CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N",
            "version": "3.0"
          }
        }
      ],
      "problemTypes": [
        {
          "descriptions": [
            {
              "cweId": "CWE-494",
              "description": "CWE-494 Download of Code Without Integrity Check",
              "lang": "en",
              "type": "CWE"
            }
          ]
        }
      ],
      "providerMetadata": {
        "dateUpdated": "2026-08-03T07:09:35.262Z",
        "orgId": "c09c270a-b464-47c1-9133-acb35b22c19a",
        "shortName": "@huntr_ai"
      },
      "references": [
        {
          "url": "https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"
        }
      ],
      "source": {
        "advisory": "659ccf6d-12d4-4d4a-84c0-078633c35a5d",
        "discovery": "EXTERNAL"
      },
      "title": "Improper Input Validation in nltk/nltk"
    }
  },
  "cveMetadata": {
    "assignerOrgId": "c09c270a-b464-47c1-9133-acb35b22c19a",
    "assignerShortName": "@huntr_ai",
    "cveId": "CVE-2026-12259",
    "datePublished": "2026-08-03T07:09:35.262Z",
    "dateReserved": "2026-06-15T09:55:01.162Z",
    "dateUpdated": "2026-08-03T14:59:01.815Z",
    "state": "PUBLISHED"
  },
  "dataType": "CVE_RECORD",
  "dataVersion": "5.2",
  "vulnerability-lookup:meta": {
    "epss": {
      "cve": "CVE-2026-12259",
      "date": "2026-08-03",
      "epss": "0.001",
      "percentile": "0.01031"
    },
    "nvd": "{\"cve\":{\"id\":\"CVE-2026-12259\",\"sourceIdentifier\":\"security@huntr.dev\",\"published\":\"2026-08-03T08:17:17.880\",\"lastModified\":\"2026-08-03T16:16:26.887\",\"vulnStatus\":\"Received\",\"cveTags\":[],\"descriptions\":[{\"lang\":\"en\",\"value\":\"In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.\"}],\"affected\":[{\"source\":\"security@huntr.dev\",\"affectedData\":[{\"vendor\":\"nltk\",\"product\":\"nltk/nltk\",\"versions\":[{\"version\":\"unspecified\",\"lessThanOrEqual\":\"latest\",\"versionType\":\"custom\",\"status\":\"affected\"}]}]}],\"metrics\":{\"cvssMetricV30\":[{\"source\":\"security@huntr.dev\",\"type\":\"Secondary\",\"cvssData\":{\"version\":\"3.0\",\"vectorString\":\"CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N\",\"baseScore\":5.3,\"baseSeverity\":\"MEDIUM\",\"attackVector\":\"NETWORK\",\"attackComplexity\":\"HIGH\",\"privilegesRequired\":\"NONE\",\"userInteraction\":\"REQUIRED\",\"scope\":\"UNCHANGED\",\"confidentialityImpact\":\"NONE\",\"integrityImpact\":\"HIGH\",\"availabilityImpact\":\"NONE\"},\"exploitabilityScore\":1.6,\"impactScore\":3.6}],\"ssvcV203\":[{\"source\":\"134c704f-9b21-4f2e-91b3-4a467353bcc0\",\"ssvcData\":{\"timestamp\":\"2026-08-03T14:55:19.698104Z\",\"id\":\"CVE-2026-12259\",\"options\":[{\"exploitation\":\"none\"},{\"automatable\":\"no\"},{\"technicalImpact\":\"partial\"}],\"role\":\"CISA Coordinator\",\"version\":\"2.0.3\"}}]},\"weaknesses\":[{\"source\":\"security@huntr.dev\",\"type\":\"Secondary\",\"description\":[{\"lang\":\"en\",\"value\":\"CWE-494\"}]}],\"references\":[{\"url\":\"https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d\",\"source\":\"security@huntr.dev\"}]}}",
    "vulnrichment": {
      "containers": "{\"cna\": {\"title\": \"Improper Input Validation in nltk/nltk\", \"providerMetadata\": {\"orgId\": \"c09c270a-b464-47c1-9133-acb35b22c19a\", \"shortName\": \"@huntr_ai\", \"dateUpdated\": \"2026-08-03T07:09:35.262Z\"}, \"descriptions\": [{\"lang\": \"en\", \"value\": \"In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.\"}], \"affected\": [{\"vendor\": \"nltk\", \"product\": \"nltk/nltk\", \"versions\": [{\"version\": \"unspecified\", \"status\": \"affected\", \"versionType\": \"custom\", \"lessThanOrEqual\": \"latest\"}]}], \"references\": [{\"url\": \"https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d\"}], \"metrics\": [{\"cvssV3_0\": {\"version\": \"3.0\", \"attackComplexity\": \"HIGH\", \"attackVector\": \"NETWORK\", \"availabilityImpact\": \"NONE\", \"confidentialityImpact\": \"NONE\", \"integrityImpact\": \"HIGH\", \"privilegesRequired\": \"NONE\", \"scope\": \"UNCHANGED\", \"userInteraction\": \"REQUIRED\", \"vectorString\": \"CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N\", \"baseScore\": 5.3, \"baseSeverity\": \"MEDIUM\"}}], \"problemTypes\": [{\"descriptions\": [{\"type\": \"CWE\", \"lang\": \"en\", \"description\": \"CWE-494 Download of Code Without Integrity Check\", \"cweId\": \"CWE-494\"}]}], \"source\": {\"advisory\": \"659ccf6d-12d4-4d4a-84c0-078633c35a5d\", \"discovery\": \"EXTERNAL\"}}, \"adp\": [{\"title\": \"CISA ADP Vulnrichment\", \"metrics\": [{\"other\": {\"type\": \"ssvc\", \"content\": {\"id\": \"CVE-2026-12259\", \"role\": \"CISA Coordinator\", \"options\": [{\"Exploitation\": \"none\"}, {\"Automatable\": \"no\"}, {\"Technical Impact\": \"partial\"}], \"version\": \"2.0.3\", \"timestamp\": \"2026-08-03T14:55:19.698104Z\"}}}], \"providerMetadata\": {\"orgId\": \"134c704f-9b21-4f2e-91b3-4a467353bcc0\", \"shortName\": \"CISA-ADP\", \"dateUpdated\": \"2026-08-03T14:58:56.144Z\"}}]}",
      "cveMetadata": "{\"cveId\": \"CVE-2026-12259\", \"assignerOrgId\": \"c09c270a-b464-47c1-9133-acb35b22c19a\", \"state\": \"PUBLISHED\", \"assignerShortName\": \"@huntr_ai\", \"dateReserved\": \"2026-06-15T09:55:01.162Z\", \"datePublished\": \"2026-08-03T07:09:35.262Z\", \"dateUpdated\": \"2026-08-03T14:59:01.815Z\"}",
      "dataType": "CVE_RECORD",
      "dataVersion": "5.2"
    }
  }
}

GHSA-PV39-QRFQ-G8GC

Vulnerability from github – Published: 2026-08-03 09:32 – Updated: 2026-08-03 09:32

Details

In nltk version 3.9.4, the nltk.downloader.Downloader._download_package() function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for info.url through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.

Severity

5.3 (Medium)


                  
                    CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N

Show details on source website

JSON

To clipboard

{
  "affected": [],
  "aliases": [
    "CVE-2026-12259"
  ],
  "database_specific": {
    "cwe_ids": [
      "CWE-494"
    ],
    "github_reviewed": false,
    "github_reviewed_at": null,
    "nvd_published_at": "2026-08-03T08:17:17Z",
    "severity": "MODERATE"
  },
  "details": "In nltk version 3.9.4, the `nltk.downloader.Downloader._download_package()` function writes downloaded package bytes to disk and may extract them before enforcing SHA-256 or MD5 checksum validation. This allows an attacker to tamper with the package response body for `info.url` through a compromised mirror, malicious proxy, or other source-substitution condition, leading to the installation of attacker-controlled package bytes. The vulnerability can result in malicious corpus or model content being trusted by downstream users or applications.",
  "id": "GHSA-pv39-qrfq-g8gc",
  "modified": "2026-08-03T09:32:37Z",
  "published": "2026-08-03T09:32:37Z",
  "references": [
    {
      "type": "ADVISORY",
      "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-12259"
    },
    {
      "type": "WEB",
      "url": "https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"
    }
  ],
  "schema_version": "1.4.0",
  "severity": [
    {
      "score": "CVSS:3.0/AV:N/AC:H/PR:N/UI:R/S:U/C:N/I:H/A:N",
      "type": "CVSS_V3"
    }
  ]
}

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.

Detection rules are retrieved from Rulezet.

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.

Action not permitted

CVE-2026-12259 (GCVE-0-2026-12259)

GHSA-PV39-QRFQ-G8GC

Tags

Sightings

Nomenclature