EUVD-2026-66396
GHSA-2rrw-hpqm-36pv
Severity by source
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
Network vector with no auth or user interaction assumed for worst-case exposed endpoint; availability-only impact, no confidentiality or integrity effect.
Primary rating from Vendor (VulnCheck).
CVSS VectorVendor: VulnCheck
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
Lifecycle Timeline
3DescriptionCVE.org
NLTK versions before 3.10.0 contain a regular expression denial of service vulnerability in Text.findall() and TokenSearcher.findall() methods that accept user-supplied regular expressions without validation or timeout. Attackers can supply crafted regex patterns that cause catastrophic backtracking, resulting in indefinite CPU saturation and denial of service to all users of the Python process.
AnalysisAI
Catastrophic regex backtracking in NLTK before 3.10.0 allows unauthenticated remote attackers to saturate CPU and deny service to all users sharing the Python process by supplying crafted patterns to the Text.findall() or TokenSearcher.findall() methods. Any Python application that exposes NLTK regex search functionality to user-controlled input is affected across all platforms. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires the target Python application to pass attacker-controlled strings as regex patterns directly to NLTK's Text.findall() or TokenSearcher.findall() methods without prior sanitization or timeout enforcement. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 score of 8.7 (AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N) reflects worst-case network-exposed deployment with no authentication barrier. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker identifies a web application that accepts a search query and passes it as a regex to NLTK's Text.findall() - for example, a corpus search tool or NLP API. The attacker submits a payload such as the pattern (a+)+b against a long string of 'a' characters, causing the Python re engine to explore exponentially many backtracking paths. … |
| Remediation | Upgrade NLTK to version 3.10.0 or later, which is the vendor-confirmed fix version per the GitHub security advisory at https://github.com/nltk/nltk/security/advisories/GHSA-rrv8-h7p8-rx55. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: inventory all applications using NLTK (check requirements.txt, setup.py, and pip lists in production environments) and identify which expose Text.findall() or TokenSearcher.findall() to untrusted input; prioritize by user-facing criticality. …
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External POC / Exploit Code
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