EUVD-2026-67074
GHSA-pf76-q698-37v8
Severity by source
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/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-reachable with no authentication or user interaction; impact is limited to low application availability - no confidentiality, integrity, or scope-change effect applies.
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:L/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
2DescriptionCVE.org
NLTK before 3.10.3 contains an uncontrolled recursion vulnerability in nltk.featstruct.FeatStructReader that allows unauthenticated attackers to cause a denial of service by supplying deeply nested feature-structure input. Attackers can craft trivial payloads with nested brackets that exceed Python's recursion limit and raise an unhandled RecursionError, crashing applications that parse user-supplied feature structures or feature grammars.
AnalysisAI
Uncontrolled recursion in NLTK's FeatStructReader component (all versions before 3.10.3) enables unauthenticated remote attackers to crash any Python application that parses user-supplied feature structures or feature grammars. Attackers submit trivially crafted payloads containing deeply nested brackets, exhausting Python's call stack and raising an unhandled RecursionError that terminates the application process. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that the target application passes user-controlled input directly to `nltk.featstruct.FeatStructReader` (or a feature grammar parser that internally invokes it) without enforcing a nesting-depth limit. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 base score of 6.9 reflects network reachability with no authentication, complexity, or user-interaction barrier, but constrains impact to low vulnerable-system availability (VA:L) with no confidentiality or integrity effect (VC:N/VI:N) and no subsequent-system impact (SC:N/SI:N/SA:N). … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker submits a crafted string such as `[f1=[f2=[f3=[...]]]]` with hundreds or thousands of nested bracket levels to any HTTP endpoint or input field that passes the value to `nltk.featstruct.FeatStructReader`. The parser recurses without a depth guard, rapidly exceeding Python's recursion limit, and the resulting unhandled RecursionError terminates the worker process or application thread. … |
| Remediation | The primary fix is to upgrade NLTK to version 3.10.3 or later, as confirmed by the vendor advisory at https://github.com/nltk/nltk/security/advisories/GHSA-cw6x-m8jw-qmrh. … Detailed patch versions, workarounds, and compensating controls in full report. |
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Same weakness CWE-674 – Uncontrolled Recursion
View allSame technique Denial Of Service
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External POC / Exploit Code
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