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Back to active CVEs
High · CVSS 8.7CVE-2026-126303

NLTK before 3.10.4 Denial of Service via SteppingRecursiveDescentParser.parse()CVE-2026-126303

Answer in brief

CVE-2026-126303 records a High severity (CVSS 8.7) vulnerability in NLTK before 3.10.4 Denial of Service via SteppingRecursiveDescentParser.parse(). The current sources do not mark it as known exploited. The current feed maps nltk/nltk (generic). Check affected ranges and fixed versions before updating.

Analysis pending evidence review

HOL Guard separates source facts from reviewed analysis. See the methodology.

Published Nov 13, 2026Updated Nov 13, 2026Source checked Nov 13, 2026First seen by HOL Nov 13, 2026Material review Nov 13, 2026
Upstream Advisory

Key facts

Risk
High · CVSS 8.7
Exploitation
Not marked as known exploited
Affected software
1 mapped package or product
Fix availability
Available

Why this deserves its current priority

CVSS is 8.7. 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.

Affected scope and exposure questions

The current feed maps nltk/nltk (generic). Check affected ranges and fixed versions before updating.

Mapped affected packages and fixed versions
PackageAffected rangeFixed version
nltk/nltkgeneric>=0 <3.10.43.10.4

Recommended response

  1. 1Check inventory. Check lockfiles and deployed manifests for nltk/nltk.
  2. 2Review the reported fix. Update nltk/nltk to 3.10.4 if you use the affected versions. Test the change in a non-production environment first.

Evidence timeline and material changes

  1. Published upstream

    Nov 13, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  2. Source modified

    Nov 13, 2026

    Evidence: source:cvelist:source_dates:source-dates:record

  3. First seen by HOL

    Nov 13, 2026

Sources and claim methodology

  • GitHub security advisorygithub.com
  • Source referencevulncheck.com
Upstream source description

NLTK before 3.10.4 contains an uncontrolled resource consumption vulnerability in SteppingRecursiveDescentParser.parse() that lacks any max_time deadline or step limit. Attackers influencing the grammar can supply an ambiguous self-embedding grammar and short token input to force unbounded top-down search, pinning CPU cores and exhausting worker pools.

Quoted source text, attributed separately from HOL analysis.

Record context

Vulnerability class
Secret Exfiltration
EPSS
Not reported
CWE IDs
CWE-400
Source
CVE List V5
Source checked
Nov 13, 2026
References
2 linked sources
Open source record