CVSS 4.0
6.9 mediumCVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:NCVE-2026-126300 NLTK from 3.2.5 before 3.10.4 CPU Exhaustion via TreebankWordTokenizer.span_tokenize
Medium (6.9) in nltk nltk. EPSS 0.5% estimated probability of exploitation activity in the next 30 days. Fixed in nltk 3.10.4.
On this page
NLTK from 3.2.5 before 3.10.4 contains an algorithmic complexity vulnerability in TreebankWordTokenizer.span_tokenize that allows remote attackers to cause quadratic CPU consumption through repeated list.pop(0) calls. Attackers can submit long runs of double-quote characters to services span-tokenizing untrusted text, exhausting a CPU core and degrading availability.
Severity
CVSS 3.1
5.3 mediumCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:L- EPSS
- 0.5% estimated probability of exploitation activity in the next 30 days; 44th percentile. Scored 2026-11-13. A forecast for this CVE across the internet, not for your own systems.
- CWE
- CWE-407 Inefficient Algorithmic Complexity
- Published
- Modified
- Assigned by
- VulnCheck (CNA)
- NVD analysis
- Awaiting analysis
- Record from
- the NVD, synced
Ask an AI about this CVE
Show the prompt
Explain CVE-2026-126300 for an engineer deciding whether to act. Use https://cve.bz/api/public/cves/CVE-2026-126300?via=ask-ai-copy and https://cve.bz/cve/CVE-2026-126300?via=ask-ai-copy as the source of truth: what is affected and which versions fix it, whether it is in CISA KEV, public exploits, and its EPSS (an internet-wide 30-day estimate of exploitation activity, not a forecast for my systems). If they give no fixed versions, use the CVE record https://cveawg.mitre.org/api/cve/CVE-2026-126300 or the vendor advisory, not third-party mirrors. Tell me how to check whether I am affected and how to verify a fix. Cite the sources and say where they are uncertain.Opens a third-party assistant; its answer is its own, not cve.bz's. The prompt holds only this CVE's id and public links.
Badge for a README or a site
An image that stays current: it is drawn from the data each time it is fetched (a host that proxies images, as GitHub does, may show its copy for a while). Markdown:
[](https://cve.bz/cve/CVE-2026-126300)
HTML:
<a href="https://cve.bz/cve/CVE-2026-126300"><img src="https://cve.bz/cve/badge/CVE-2026-126300.svg" alt="CVE-2026-126300"></a>
Affected
Versions
From the CNA's record in the CVE List.
| Product | Affected |
|---|---|
| nltk | from 3.2.5 before 3.10.4 |
Fix and patched versions
nltk(PyPI): fixed in 3.10.4
Packages (OSV)
| Advisory | Ecosystem | Package | Affected | Fixed in |
|---|---|---|---|---|
| GHSA-ffr9-mgrr-wcvr | PyPI | nltk | >=3.2.5 <3.10.4 | 3.10.4 |