Answer in brief
CVE-2026-66393 records a Medium severity (CVSS 7.5) vulnerability in NLTK before 3.9.4 Denial of Service via JSONTaggedDecoder. The current sources do not mark it as known exploited. The current feed maps nltk/nltk (generic), nltk (pip), nltk (pypi), nltk (pypi). Check affected ranges and fixed versions before updating.
Analysis pending evidence review
HOL Guard separates source facts from reviewed analysis. See the methodology.
CVSS is 7.5. The current sources do not mark it as known exploited. Treat this as a source-backed prioritization signal, not a statement about your environment.
Analysis status
Analysis pending evidence review
Factual feed record only; HOL analysis is not approved for indexing. Read the methodology.
The current feed maps nltk/nltk (generic), nltk (pip), nltk (pypi), nltk (pypi). Check affected ranges and fixed versions before updating.
| Product | Affected versions | Fixed versions |
|---|---|---|
| cpe:2.3:a:nltk:nltk:*:*:*:*:*:*:*:* | Not reported | Not reported |
| Package | Affected range | Fixed version |
|---|---|---|
| nltk/nltkgeneric | >=0 <3.9.4 | 3.9.4 |
| nltkpip | <=3.9.3 | 3.9.4 |
| nltkpypi | >=0 | Not reported |
| nltkpypi | >=0 <3.9.4 | 3.9.4 |
Published upstream
Aug 22, 2026
Evidence: source:cvelist:source_dates:source-dates:recordSource modified
Sep 4, 2026
Evidence: source:cvelist:source_dates:source-dates:recordFirst seen by HOL
Aug 22, 2026
NLTK versions before 3.9.4 contain an unbounded recursion vulnerability in JSONTaggedDecoder.decode_obj() that allows attackers to cause denial of service by supplying deeply nested JSON structures. Attackers can craft JSON payloads exceeding the recursion limit to trigger an unhandled RecursionError that crashes the Python process.
Quoted source text, attributed separately from HOL analysis.