EUVD-2026-65227
GHSA-jx89-3qg8-p2mr
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-reachable XML parser requires no authentication; only availability impacted via memory exhaustion; scope unchanged as impact is confined to the vulnerable process.
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 3.10.3 use xml.etree.ElementTree to parse XML in multiple modules, which honors entity declarations in document DTDs. Attackers can craft XML payloads with nested entity declarations that expand from hundreds of bytes to megabytes in memory, causing denial of service.
AnalysisAI
XML Entity Expansion (Billion Laughs) in NLTK before 3.10.3 allows unauthenticated remote attackers to cause denial of service by submitting crafted XML payloads with nested entity declarations that expand exponentially in memory. Multiple NLTK modules rely on Python's xml.etree.ElementTree parser, which honors DTD entity definitions, making them susceptible to this class of attack. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires that attacker-controlled or untrusted XML data reaches one of NLTK's internal modules that invoke xml.etree.ElementTree for parsing - versions prior to 3.10.3 only. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 4.0 vector AV:N/AC:L/AT:N/PR:N/UI:N/VA:H yields a score of 8.7, reflecting a remotely exploitable, unauthenticated, low-complexity DoS with high availability impact on the vulnerable system. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | An attacker identifies an application that accepts user-supplied XML data and routes it through an NLTK module for processing. They submit a classic Billion Laughs payload - a document with a small DTD section defining a chain of entities each referencing the previous, starting from a few hundred bytes - against the endpoint. … |
| Remediation | Upgrade NLTK to version 3.10.3 or later, which is the vendor-released patch per the description. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours, inventory all systems running NLTK versions prior to 3.10.3 and identify which handle untrusted XML input; prioritize exposure assessment by application criticality. …
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Same technique Denial Of Service
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External POC / Exploit Code
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