High severity7.5NVD Advisory· Published Aug 22, 2026· Updated Aug 27, 2026
CVE-2026-66393
CVE-2026-66393
Description
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.
AI Insight
LLM-synthesized narrative grounded in this CVE's description and references.
Affected packages
Versions sourced from the GitHub Security Advisory.
| Package | Affected versions | Patched versions |
|---|---|---|
nltkPyPI | < 3.9.4 | 3.9.4 |
Affected products
16- osv-coords15 versionspkg:apk/chainguard/apache-beam-python-3.11-sdkpkg:apk/chainguard/apache-beam-python-3.12-sdkpkg:apk/chainguard/apache-beam-python-3.13-sdkpkg:apk/chainguard/kubeflow-pipelines-visualization-serverpkg:apk/chainguard/label-studiopkg:apk/chainguard/nemopkg:apk/chainguard/open-webuipkg:apk/chainguard/py3.11-nltkpkg:apk/chainguard/py3.12-nltkpkg:apk/chainguard/py3.13-nltkpkg:apk/wolfi/kubeflow-pipelines-visualization-serverpkg:apk/wolfi/open-webuipkg:apk/wolfi/py3.11-nltkpkg:apk/wolfi/py3.12-nltkpkg:apk/wolfi/py3.13-nltk
< 2.71.0-r8+ 14 more
- (no CPE)range: < 2.71.0-r8
- (no CPE)range: < 2.71.0-r2
- (no CPE)range: < 2.71.0-r2
- (no CPE)range: < 2.16.0-r3
- (no CPE)range: < 1.23.0-r1
- (no CPE)range: < 2.7.2-r1
- (no CPE)range: < 0.8.12-r2
- (no CPE)range: < 3.9.4-r0
- (no CPE)range: < 3.9.4-r0
- (no CPE)range: < 3.9.4-r0
- (no CPE)range: < 2.16.0-r3
- (no CPE)range: < 0.8.12-r2
- (no CPE)range: < 3.9.4-r0
- (no CPE)range: < 3.9.4-r0
- (no CPE)range: < 3.9.4-r0
Patches
Vulnerability mechanics
References
6- github.com/nltk/nltk/security/advisories/GHSA-rf74-v2fm-23pwnvdExploitMitigationVendor AdvisoryWEB
- github.com/advisories/GHSA-rf74-v2fm-23pwghsaADVISORY
- nvd.nist.gov/vuln/detail/CVE-2026-66393ghsaADVISORY
- www.vulncheck.com/advisories/nltk-before-denial-of-service-via-jsontaggeddecodernvdThird Party AdvisoryWEB
- github.com/nltk/nltk/commit/00cdcd392142e6c745e7120c8d50a24127df5fadghsaWEB
- github.com/pypa/advisory-database/tree/main/vulns/nltk/PYSEC-2026-3724.yamlghsaWEB
News mentions
1- NLTK: Thirteen Path Traversal, RCE, and DoS Vulnerabilities Disclosed TogetherVypr Intelligence · Aug 22, 2026