NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The _tgrep_node_action function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or timeout. An attacker who controls the tgrep pattern (e.g., via tgrep_positions() or tgrep_compile() exposed to external input) can supply a pattern that triggers catastrophic backtracking, causing indefinite CPU saturation that blocks the Python process.
CVE-2026-80206
MEDIUMPre-NVD 5.95.9—Trending — 3 sources updated this weekElevated
EchelonGraph scoreMEDIUM confidence
This medium-severity CVE scores 5.9 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 0.2%, top 84% of all CVEs by exploit prediction. 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).
Triggered by: NVD CVSS baseline
Sources: epss, secondary
5.9EG
EchelonGraph verdictMonitorLow exploitation likelihood right now — keep watching.
- Lower severity and no public exploit yet
CISA-KEV: Not listedEPSS PROB: 0%CVSS: 5.9Exploit: Elevated riskExposed: 0
No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.
- CVSS v3
- 5.9
- EG Score
- 5.9(medium)
- EG Risk
- 43(Track)EG Risk 43/100SSVC: 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 computedSeverity59% × 45%Exploitation40% × 40%Automatability0% × 15%Action: Routine — remediate on your standard cadence. - EPSS PROB
- 0%
- EPSS %ILE
- 16%
- KEV
- Not listed
Published
August 26, 2026
Last Modified
August 26, 2026
Advisory Details (2)
Auto-updated Aug 26, 2026🔬 Proof of concept available. Patch available. Sources: github.
generic
NLTK 3.10.2 Regular Expression Denial of Service via tgrep | Advisories | VulnCheck
https://www.vulncheck.com/advisories/nltk-3.10.2-regular-expression-denial-of-service-via-tgrepgithub Patch Available🟡 PoC Available
ReDoS in nltk.tgrep via unvalidated user-supplied regular expressions · Advisory · nltk/nltk · GitHub
https://github.com/nltk/nltk/security/advisories/GHSA-w3v8-gmh9-3wv7Weakness Classification(1)
MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.
Data Freshness Timeline
(refreshed 10× in last 7d / 10× 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.
- 2026-08-30 02:03 UTCEG score recompute
- 2026-08-30 01:22 UTCEPSS rescore
- 2026-08-28 23:58 UTCEG score recompute
- 2026-08-28 21:42 UTCEPSS rescore
- 2026-08-27 18:07 UTCEG score recompute
- 2026-08-27 14:25 UTCEPSS rescore
- 2026-08-26 15:53 UTCEG score recompute
- 2026-08-26 12:58 UTCEG score recompute
- 2026-08-26 10:48 UTCEG score recompute
- 2026-08-26 10:47 UTCMITRE cvelistV5first tracked
Related CVEs(same CWE)
Frequently asked(5)
What is CVE-2026-80206?
CVE-2026-80206 is a medium vulnerability published on August 26, 2026. NLTK before 3.10.3 contains a regular expression denial of service (ReDoS) vulnerability in the tgrep module. The tgrepnodeaction function compiles user-supplied regular expressions embedded in /regex/ pattern nodes and executes them via re.search against tree node labels without any validation or…
When was CVE-2026-80206 disclosed?
CVE-2026-80206 was first published in the National Vulnerability Database on August 26, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-80206 actively exploited?
CVE-2026-80206 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 0% probability of exploitation in the next 30 days, which ranks it in the top 83.8% of all scored CVEs.
What is the CVSS score of CVE-2026-80206?
CVE-2026-80206 has a CVSS v3 base score of 5.9 (NVD).
How do I remediate CVE-2026-80206?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-80206, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.
Dependency Blast Radius
Explore the affected products and dependency analysis for CVE-2026-80206
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