CVE-2026-72818Public exploitNetwork attack vector

Service interrupt via URL regex backtracking

Published Aug 20, 2026 · Updated Aug 20, 2026

Regular expression denial of service in TweetTokenizer in NLTK before 3.10.1 allows remote attackers to interrupt service via crafted text. The URLS pattern in nltk/tokenize/casual.py compiles a naked-domain branch into TweetTokenizer.WORD_RE where an unbounded domain-label prefix backtracks across exponentially many partitions when no trailing top-level domain is present. Any service that tokenizes untrusted social-media text with TweetTokenizer or casual_tokenize can be stalled per request without authentication, with CPU exhaustion but no reported data read or code execution.

CVSS severity7.5
High
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Regular expression denial of service in TweetTokenizer in NLTK before 3.10.1 allows remote attackers to interrupt service via crafted text. The URLS pattern in nltk/tokenize/casual.py compiles a naked-domain branch into TweetTokenizer.WORD_RE where an unbounded domain-label prefix backtracks across exponentially many partitions when no trailing top-level domain is present. Any service that tokenizes untrusted social-media text with TweetTokenizer or casual_tokenize can be stalled per request without authentication, with CPU exhaustion but no reported data read or code execution.

The record

CVE
CVE-2026-72818
Published
Aug 20, 2026
Updated
Aug 20, 2026
Vendor
NLTK Project
Product
NLTK
Classifications
CWE-1333, T1499
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 20, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 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 <3.10.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

NLTK Project · NLTKversion=0 <3.10.1

Published CVSS scores

7.5VulnCheckCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
8.7VulnCheckCVSS: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-1333Inefficient Regular Expression Complexity
T1499Endpoint Denial of Service

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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