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.
CVE-2026-72818
This high-severity CVE scores 7.5 under the CNA's CVSS (NVD's own analysis pending). EPSS exploit-prediction score not yet available (the EPSS model rescores nightly; freshly-published CVEs typically appear within 48 hours). GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).
- High severity, but no confirmed exploitation yet
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 7.5
- EG Score
- 7.5(low)
- EG Risk
- 38(Track)EG Risk 38/100SSVC: Track
EG Risk is EchelonGraph's 0–100 priority score: it fuses intrinsic severity with real-world exploitation and automatability so you can rank equal-severity CVEs and fix the most dangerous first. Higher = act sooner. Distinct from the 0–10 EG Score (severity).
How it’s computedSeverity75% × 45%Exploitation0% × 40%Automatability30% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
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- EPSS %ILE
- —
- KEV
- Not listed
Published
August 20, 2026
Last Modified
August 20, 2026
Advisory Details (4)
Auto-updated Aug 20, 2026NLTK TweetTokenizer URL Pattern Backtracks Catastrophically on Naked-Domain-Like Input | Advisories | VulnCheck
https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-inputReDoS (catastrophic backtracking) in `TweetTokenizer` URL regex (naked-domain branch) · Issue #3704 · nltk/nltk · GitHub
https://github.com/nltk/nltk/issues/3704nltk/nltk/tokenize/casual.py at 3.9.4 · nltk/nltk · GitHub
https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.pyVendor Advisories for CVE-2026-72818(1)
These vendors published their own advisory mentioning this CVE — often with vendor-specific remediation steps + affected product lists not in NVD.
Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 4× in last 7d / 4× in last 30d)
Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.
- 2026-08-20 23:42 UTCEG score recompute
- 2026-08-20 22:23 UTCEG score recompute
- 2026-08-20 22:07 UTCEG score recompute
- 2026-08-20 22:07 UTCMITRE cvelistV5first tracked
Frequently asked(4)
What is CVE-2026-72818?
When was CVE-2026-72818 disclosed?
What is the CVSS score of CVE-2026-72818?
How do I remediate CVE-2026-72818?
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-72818
Is Your Infrastructure Affected by CVE-2026-72818?
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