CVE-2026-78681Public exploitNetwork attack vectorHinoki check available

Service interruption via recursive XML entity expansion

Published Aug 25, 2026 · Updated Aug 26, 2026

XML entity expansion in NLTK before 3.10.3 allows remote attackers to interrupt consuming services via crafted XML documents. Raw ElementTree parsing in ElementWrapper, named_entity, and downloader call sites honors nested DTD entity declarations and expands a small input into megabytes of memory. Exploitation requires an application to pass attacker-controlled XML to an affected call site; the resulting memory consumption is limited to availability impact.

CVSS severity8.7
High
EPSS probability0.29%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkAvailable
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Summary

What happened

XML entity expansion in NLTK before 3.10.3 allows remote attackers to interrupt consuming services via crafted XML documents. Raw ElementTree parsing in ElementWrapper, named_entity, and downloader call sites honors nested DTD entity declarations and expands a small input into megabytes of memory. Exploitation requires an application to pass attacker-controlled XML to an affected call site; the resulting memory consumption is limited to availability impact.

The record

CVE
CVE-2026-78681
Published
Aug 25, 2026
Updated
Aug 26, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-776, CAPEC-197, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 25, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 26, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=0 <3.10.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=0 <3.10.3

Published CVSS scores

7.5VulnCheck CNACVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7VulnCheck CNACVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-776Improper Restriction of Recursive Entity References in DTDs ('XML Entity Expansion')
CAPEC-197Exponential Data Expansion
T1499.004Application or System Exploitation

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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