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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." } ], "problemTypes": [ { "descriptions": [ { "lang": "en", "description": "Inefficient Regular Expression Complexity", "cweId": "CWE-1333", "type": "CWE" } ] } ], "affected": [ { "vendor": "nltk", "product": "nltk", "defaultStatus": "unaffected", "packageURL": "pkg:pypi/nltk", "collectionURL": "https://pypi.org", "packageName": "nltk", "repo": "https://github.com/nltk/nltk", "versions": [ { "version": "0", "lessThan": "3.10.1", "status": "affected", "versionType": "semver" }, { "version": "3.10.1", "status": "unaffected", "versionType": "semver" } ], "programFiles": [ "nltk/tokenize/casual.py" ] } ], "cpeApplicability": [ { "nodes": [ { "operator": "OR", "negate": false, "cpeMatch": [ { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.9.3:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.9.2:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.9.1:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.9:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.9:beta1:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.8.1:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.8:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.7:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.6.5:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.6.6:*:*:*:*:*:*:*" }, { "vulnerable": true, "criteria": "cpe:2.3:a:nltk:nltk:3.6.7:*:*:*:*:*:*:*" } ] } ] } ], "metrics": [ { "format": "CVSS", "cvssV4_0": { "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", "attackVector": "NETWORK", "attackComplexity": "LOW", "attackRequirements": "NONE", "privilegesRequired": "NONE", "userInteraction": "NONE", "vulnConfidentialityImpact": "NONE", "vulnIntegrityImpact": "NONE", "vulnAvailabilityImpact": "HIGH", "subConfidentialityImpact": "NONE", "subIntegrityImpact": "NONE", "subAvailabilityImpact": "NONE", "baseScore": 8.7, "baseSeverity": "HIGH" } }, { "format": "CVSS", "cvssV3_1": { "version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "NONE", "integrityImpact": "NONE", "availabilityImpact": "HIGH", "baseScore": 7.5, "baseSeverity": "HIGH" } } ], "references": [ { "url": "https://github.com/nltk/nltk/issues/3704", "tags": [ "issue-tracking" ], "name": "GitHub Issue #3704" }, { "url": "https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.py", "tags": [ "technical-description" ], "name": "Unbounded naked-domain branch in the URLS pattern at 3.9.4" }, { "url": "https://github.com/nltk/nltk/releases/tag/v3.10.1", "tags": [ "release-notes" ], "name": "NLTK v3.10.1 Release Notes" }, { "url": "https://github.com/nltk/nltk", "tags": [ "product" ] }, { "name": "VulnCheck Advisory: NLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like Input", "tags": [ "third-party-advisory" ], "url": "https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-input" } ], "credits": [ { "lang": "en", "value": "George Chen", "type": "reporter" } ], "x_generator": { "engine": "vulncheck-endgame" } }, "adp": [ { "references": [ { "url": "https://github.com/nltk/nltk/issues/3704", "tags": [ "exploit" ] } ], "metrics": [ { "other": { "type": "ssvc", "content": { "timestamp": "2026-08-21T11:05:49.886911Z", "id": "CVE-2026-72818", "options": [ { "Exploitation": "poc" }, { "Automatable": "yes" }, { "Technical Impact": "partial" } ], "role": "CISA Coordinator", "version": "2.0.3" } } } ], "title": "CISA ADP Vulnrichment", "providerMetadata": { "orgId": "134c704f-9b21-4f2e-91b3-4a467353bcc0", "shortName": "CISA-ADP", "dateUpdated": "2026-08-21T11:06:07.858Z" } } ] } }