High [CVE-2026-72818] Denial of Service via crafted URL input
This high-severity Red Hat Linux advisory covers CVE-2026-72818 affecting Lightspeed Core, OpenShift Lightspeed, Red Hat Ansible Automation Platform 2.
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Summary
The URLS regular expression in nltk/tokenize/casual.py, compiled into TweetTokenizer.WORD_RE and applied by TweetTokenizer.tokenize, contains a naked-domain branch whose domain-label prefix [a-z0-9]+(?:[.\-][a-z0-9]+)* is unbounded.
Input consisting of many alternating label separators can be partitioned in exponentially many ways, and because the branch also requires a trailing top-level domain that such input never supplies, the engine explores those partitions before failing at each offset.
A few kilobytes of input therefore consumes seconds to minutes of single-threaded CPU, and the HANG_RE substitution performed before matching does not collapse the pattern.
TweetTokenizer is intended for tokenizing untrusted social-media text, so any service that applies it, or the module-level casual_tokenize, to submitted text can be stalled per request without authentication. Version 3.10.1 bounds the label repetition.
A flaw was found in NLTK. The `TweetTokenizer` component, used for processing social media text, contains a regular expression vulnerability.
A remote unauthenticated attacker can provide specially crafted input containing many alternating label separators, causing the regular expression to backtrack catastrophically. This can lead to a Denial of Service (DoS) by consuming significant CPU resources and stalling the application.
Affected versions
No affected-version range was extracted from the source record. The vendor advisory is authoritative — check it before change work.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
Mitigation checklist
- Mitigation for this issue is either not available or the currently available options do not meet the Red Hat Product Security criteria comprising ease of use and deployment, applicability to widespread installation base, or stability.
Official advisory · high-confidence parse· fetched 1 hour ago·verify at source
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