---
cve: "CVE-2026-72818"
severity: "HIGH"
cvss: 8.7
epss: "29.6%"
vendor: "nltk"
kev: false
exploited: false
published: "2026-08-20 22:18:05"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-09-06T00:07:06+02:00"
---

# CVE-2026-72818

> 8.7 HIGH · 🧪 PoC

## Beschreibung

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.

## CVSS-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Patch verfügbar (OSV)

- 35813c85af3f13d4f7196085854eafb3d0c5db02 (Commit)

## Referenzen

- <https://github.com/nltk/nltk/issues/3704>
- <https://github.com/nltk/nltk/blob/3.9.4/nltk/tokenize/casual.py>
- <https://github.com/nltk/nltk/releases/tag/v3.10.1>
- <https://github.com/nltk/nltk>
- <https://www.vulncheck.com/advisories/nltk-tweettokenizer-url-pattern-backtracks-catastrophically-on-naked-domain-like-input>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-72818) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_