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CVE-2026-72818

Full vulnerability record from the local CVENow database.

Description

The URLS regular expression in nltk/tokenize/casual.py, compiled into TweetTokenizer.WORD_RE and applied by TweetTokenizer.tokenize, contains a naked-domain branch whose domain-label prefix [a-z0-9]+(?:[.\-][a-z0-9]+)* is unbounded. Input consisting of many alternating label separators can be partitioned in exponentially many ways, and because the branch also requires a trailing top-level domain that such input never supplies, the engine explores those partitions before failing at each offset. A few kilobytes of input therefore consumes seconds to minutes of single-threaded CPU, and the HANG_RE substitution performed before matching does not collapse the pattern. TweetTokenizer is intended for tokenizing untrusted social-media text, so any service that applies it, or the module-level casual_tokenize, to submitted text can be stalled per request without authentication. Version 3.10.1 bounds the label repetition.

Severity
HIGH
CVSS score
8.7 (v4.0)
Vulnerability status
Awaiting Analysis
Source identifier
[email protected]
Published
2026-08-20 22:18:05.087000
Last modified
2026-10-26 10:10:00.140000
View original CVE JSON 
{
  "id": "CVE-2026-72818",
  "sourceIdentifier": "[email protected]",
  "published": "2026-08-20T22:18:05.087",
  "lastModified": "2026-10-26T10:10:00.140",
  "vulnStatus": "Awaiting Analysis",
  "cveTags": [],
  "descriptions": [
    {
      "lang": "en",
      "value": "The URLS regular expression in nltk/tokenize/casual.py, compiled into TweetTokenizer.WORD_RE and applied by TweetTokenizer.tokenize, contains a naked-domain branch whose domain-label prefix [a-z0-9]+(?:[.\\-][a-z0-9]+)* is unbounded. Input consisting of many alternating label separators can be partitioned in exponentially many ways, and because the branch also requires a trailing top-level domain that such input never supplies, the engine explores those partitions before failing at each offset. A few kilobytes of input therefore consumes seconds to minutes of single-threaded CPU, and the HANG_RE substitution performed before matching does not collapse the pattern. TweetTokenizer is intended for tokenizing untrusted social-media text, so any service that applies it, or the module-level casual_tokenize, to submitted text can be stalled per request without authentication. Version 3.10.1 bounds the label repetition."
    },
    {
      "lang": "es",
      "value": "La expresión regular URLS en nltk/tokenize/casual.py, compilada en TweetTokenizer.WORD_RE y aplicada por TweetTokenizer.tokenize, contiene una rama de dominio ’desnudo’ cuyo prefijo de etiqueta de dominio [a-z0-9]+(?:[.\\-][a-z0-9]+)* es ilimitado. La entrada que consiste en muchos separadores de etiquetas alternos puede ser particionada de exponencialmente muchas maneras, y debido a que la rama también requiere un dominio de nivel superior final que dicha entrada nunca proporciona, el motor explora esas particiones antes de fallar en cada desplazamiento. Unos pocos kilobytes de entrada, por lo tanto, consume de segundos a minutos de CPU de un solo hilo, y la sustitución HANG_RE realizada antes de la coincidencia no colapsa el patrón. TweetTokenizer está diseñado para tokenizar texto no confiable de redes sociales, por lo que cualquier servicio que lo aplique, o el casual_tokenize a nivel de módulo, a texto enviado puede ser paralizado por solicitud sin autenticación. La versión 3.10.1 limita la repetición de etiquetas."
    }
  ],
  "affected": [
    {
      "source": "[email protected]",
      "affectedData": [
        {
          "vendor": "nltk",
          "product": "nltk",
          "defaultStatus": "unaffected",
          "collectionURL": "https://pypi.org",
          "packageName": "nltk",
          "programFiles": [
            "nltk/tokenize/casual.py"
          ],
          "repo": "https://github.com/nltk/nltk",
          "packageURL": "pkg:pypi/nltk",
          "versions": [
            {
              "version": "0",
              "lessThan": "3.10.1",
              "versionType": "semver",
              "status": "affected"
            },
            {
              "version": "3.10.1",
              "versionType": "semver",
              "status": "unaffected"
            }
          ]
        }
      ]
    }
  ],
  "metrics": {
    "cvssMetricV40": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "4.0",
          "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/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",
          "baseScore": 8.7,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "attackRequirements": "NONE",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "vulnConfidentialityImpact": "NONE",
          "vulnIntegrityImpact": "NONE",
          "vulnAvailabilityImpact": "HIGH",
          "subConfidentialityImpact": "NONE",
          "subIntegrityImpact": "NONE",
          "subAvailabilityImpact": "NONE",
          "exploitMaturity": "NOT_DEFINED",
          "confidentialityRequirement": "NOT_DEFINED",
          "integrityRequirement": "NOT_DEFINED",
          "availabilityRequirement": "NOT_DEFINED",
          "modifiedAttackVector": "NOT_DEFINED",
          "modifiedAttackComplexity": "NOT_DEFINED",
          "modifiedAttackRequirements": "NOT_DEFINED",
          "modifiedPrivilegesRequired": "NOT_DEFINED",
          "modifiedUserInteraction": "NOT_DEFINED",
          "modifiedVulnConfidentialityImpact": "NOT_DEFINED",
          "modifiedVulnIntegrityImpact": "NOT_DEFINED",
          "modifiedVulnAvailabilityImpact": "NOT_DEFINED",
          "modifiedSubConfidentialityImpact": "NOT_DEFINED",
          "modifiedSubIntegrityImpact": "NOT_DEFINED",
          "modifiedSubAvailabilityImpact": "NOT_DEFINED",
          "Safety": "NOT_DEFINED",
          "Automatable": "NOT_DEFINED",
          "Recovery": "NOT_DEFINED",
          "valueDensity": "NOT_DEFINED",
          "vulnerabilityResponseEffort": "NOT_DEFINED",
          "providerUrgency": "NOT_DEFINED"
        }
      }
    ],
    "cvssMetricV31": [
      {
        "source": "[email protected]",
        "type": "Secondary",
        "cvssData": {
          "version": "3.1",
          "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H",
          "baseScore": 7.5,
          "baseSeverity": "HIGH",
          "attackVector": "NETWORK",
          "attackComplexity": "LOW",
          "privilegesRequired": "NONE",
          "userInteraction": "NONE",
          "scope": "UNCHANGED",
          "confidentialityImpact": "NONE",
          "integrityImpact": "NONE",
          "availabilityImpact": "HIGH"
        },
        "exploitabilityScore": 3.9,
        "impactScore": 3.6
      }
    ],
    "ssvcV203": [
      {
        "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0",
        "ssvcData": {
          "timestamp": "2026-08-21T11:05:49.886911Z",
          "id": "CVE-2026-72818",
          "options": [
            {
              "exploitation": "poc"
            },
            {
              "automatable": "yes"
            },
            {
              "technicalImpact": "partial"
            }
          ],
          "role": "CISA Coordinator",
          "version": "2.0.3"
        }
      }
    ]
  },
  "weaknesses": [
    {
      "source": "[email protected]",
      "type": "Secondary",
      "description": [
        {
          "lang": "en",
          "value": "CWE-1333"
        }
      ]
    }
  ],
  "references": [
    {
      "url": "https://github.com/nltk/nltk",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.py",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/nltk/nltk/issues/3704",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/nltk/nltk/releases/tag/v3.10.1",
      "source": "[email protected]"
    },
    {
      "url": "https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-input",
      "source": "[email protected]"
    },
    {
      "url": "https://github.com/nltk/nltk/issues/3704",
      "source": "134c704f-9b21-4f2e-91b3-4a467353bcc0"
    }
  ]
}