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

Vulnerability from cvelistv5 – Published: 2026-08-03 07:09 – Updated: 2026-08-03 14:59
VLAI
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 · CISA-ADP (v2.0.3)
Decision recorded 2026-08-03 14:55 UTC
CWE
  • CWE-494 - Download of Code Without Integrity Check
Assigner
@huntr_ai CNA under the mitre root
CNA scorecard C 65/100 over 40 records in the last 180 days details
References
Impacted products
Vendor Product Version CPE status
nltk nltk/nltk Affected: unspecified , ≤ latest (custom)
guessed Create a notification for this product.
Show details on NVD website
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": "2026-11-01",
      "epss": "0.00101",
      "percentile": "0.00887"
    },
    "nvd": {
      "cve": {
        "affected": [
          {
            "affectedData": [
              {
                "product": "nltk/nltk",
                "vendor": "nltk",
                "versions": [
                  {
                    "lessThanOrEqual": "latest",
                    "status": "affected",
                    "version": "unspecified",
                    "versionType": "custom"
                  }
                ]
              }
            ],
            "source": "security@huntr.dev"
          }
        ],
        "configurations": [
          {
            "nodes": [
              {
                "cpeMatch": [
                  {
                    "criteria": "cpe:2.3:a:nltk:nltk:3.9.4:*:*:*:*:*:*:*",
                    "matchCriteriaId": "E0F7C7D0-ADBA-409B-9E84-D8C569B4BFB2",
                    "vulnerable": true
                  }
                ],
                "negate": false,
                "operator": "OR"
              }
            ]
          }
        ],
        "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."
          },
          {
            "lang": "es",
            "value": "En la versi\u00f3n 3.9.4 de nltk, la funci\u00f3n \u201cnltk.downloader.Downloader._download_package()\u201d escribe los bytes del paquete descargado en el disco y puede extraerlos antes de aplicar la validaci\u00f3n de suma de comprobaci\u00f3n SHA-256 o MD5. Esto permite a un atacante manipular el cuerpo de la respuesta del paquete para \u201cinfo.url\u201d a trav\u00e9s de un espejo comprometido, un proxy malicioso u otra condici\u00f3n de sustituci\u00f3n de origen, lo que lleva a la instalaci\u00f3n de bytes de paquete controlados por el atacante. La vulnerabilidad puede resultar en que contenido malicioso de corpus o modelo sea confiado por usuarios o aplicaciones posteriores."
          }
        ],
        "id": "CVE-2026-12259",
        "lastModified": "2026-10-23T22:10:00.160",
        "metrics": {
          "cvssMetricV30": [
            {
              "cvssData": {
                "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"
              },
              "exploitabilityScore": 1.6,
              "impactScore": 3.6,
              "source": "security@huntr.dev",
              "type": "Secondary"
            }
          ],
          "cvssMetricV31": [
            {
              "cvssData": {
                "attackComplexity": "LOW",
                "attackVector": "NETWORK",
                "availabilityImpact": "NONE",
                "baseScore": 6.5,
                "baseSeverity": "MEDIUM",
                "confidentialityImpact": "NONE",
                "integrityImpact": "HIGH",
                "privilegesRequired": "NONE",
                "scope": "UNCHANGED",
                "userInteraction": "REQUIRED",
                "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:N",
                "version": "3.1"
              },
              "exploitabilityScore": 2.8,
              "impactScore": 3.6,
              "source": "nvd@nist.gov",
              "type": "Primary"
            }
          ],
          "ssvcV203": [
            {
              "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
              "ssvcData": {
                "id": "CVE-2026-12259",
                "options": [
                  {
                    "exploitation": "none"
                  },
                  {
                    "automatable": "no"
                  },
                  {
                    "technicalImpact": "partial"
                  }
                ],
                "role": "CISA Coordinator",
                "timestamp": "2026-08-03T14:55:19.698104Z",
                "version": "2.0.3"
              }
            }
          ]
        },
        "published": "2026-08-03T08:17:17.880",
        "references": [
          {
            "source": "security@huntr.dev",
            "tags": [
              "Permissions Required"
            ],
            "url": "https://huntr.com/bounties/659ccf6d-12d4-4d4a-84c0-078633c35a5d"
          }
        ],
        "sourceIdentifier": "security@huntr.dev",
        "vulnStatus": "Analyzed",
        "weaknesses": [
          {
            "description": [
              {
                "lang": "en",
                "value": "CWE-494"
              }
            ],
            "source": "security@huntr.dev",
            "type": "Secondary"
          }
        ]
      }
    },
    "redhat_vex": {
      "aggregate_severity": "Moderate",
      "current_release_date": "2026-10-15T20:49:33+00:00",
      "cve": "CVE-2026-12259",
      "id": "CVE-2026-12259",
      "initial_release_date": "2026-08-03T07:09:35.262000+00:00",
      "product_status:known_affected": "14",
      "source": "Red Hat CSAF VEX",
      "status": "final",
      "title": "nltk: nltk: Installation of attacker-controlled packages due to improper checksum validation",
      "url": "https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-12259.json",
      "version": "3"
    },
    "vulnrichment": {
      "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": "2026-08-03T14:58:56.144Z",
              "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"
    }
  }
}



Log in or create an account to share your comment.




Tags
Taxonomy of the tags.




Drag nodes to arrange them. Double-click a related vulnerability to open it, or a source to visit its link. The Physics button on the left tunes the layout and the simulation; the legend at the bottom left hides or shows nodes by kind and by sighting type.

Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

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.
Vulnerability timeline

Sightings and recorded dates, grouped by day · UTC

JSON

Loading timeline…




    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.