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Response snapshot Oct 27, 2026, 13:16 UTC

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VulnerabilityCVE-2026-62388

NLTK: Default ENFORCE=False Disables All pathsec Security Controls

NLTK's pathsec.py security module defaults to ENFORCE=False (line 24), which means all 8 security validation functions only emit RuntimeWarning instead of raising exceptions when violations are detected.

Published Updated

At a glance

Exploited
Not known
Severity
8.7 High (CVSS 4.0)
Chance of exploitation
Not estimated
Sources
1 source

What to do

GitHub lists first patched versions: nltk: 3.10.0. Confirm the affected range and upgrade guidance in the exact advisory.

Read GitHub-reviewed advisory GHSA-p3m8-78j2-g5p3 (opens a new tab)

What happened

NLTK's pathsec.py security module defaults to ENFORCE=False (line 24), which means all 8 security validation functions only emit RuntimeWarning instead of raising exceptions when violations are detected.

The pathsec module was introduced as the fix for CVE-2024-39705 (arbitrary code execution via pickle) and CVE-2026-0846 (path traversal). However, with ENFORCE=False as the default:

1. pathsec.open('/etc/passwd') succeeds (reads the file, emits warning) 2. pathsec.validate_network_url('http://169.254.169.254/...') succeeds (warning only) 3. pickle.loads() via nltk.data.load() proceeds despite unsafe source (warning only)

Every security gate follows the same pattern: ```python ENFORCE = os.environ.get('NLTK_PATHSEC_ENFORCE', '').lower() in ('1', 'true', 'yes')

Continue reading

def validate_something(path): if is_violation(path): if ENFORCE: raise SecurityError('...') # Only raised when env var is set else: warnings.warn('...', RuntimeWarning) # Default: warning only # Execution continues regardless ```

This means the security remediations for CVE-2024-39705 and CVE-2026-0846 are effectively disabled by default. Any user who installed NLTK 3.9.x expecting the security fixes to be active is still vulnerable unless they manually set NLTK_PATHSEC_ENFORCE=1.

PoC: ```python import nltk.pathsec import warnings

# Show that ENFORCE is False by default print(f'ENFORCE = {nltk.pathsec.ENFORCE}') # False

# Attempt to read /etc/passwd through pathsec -- should be blocked with warnings.catch_warnings(record=True) as w: warnings.simplefilter('always') result = nltk.pathsec.open('/etc/passwd', 'r') print(f'File opened: {result.name}') # /etc/passwd print(f'Warning emitted: {w[0].message}') # RuntimeWarning (not an exception) # Attack succeeds -- file is readable ```

The correct default is fail-secure: ENFORCE should be True unless explicitly disabled. The current default makes the security module opt-in rather than opt-out, defeating its purpose.

Suggested fix: Change default to ENFORCE=True. Users who need backwards compatibility can set NLTK_PATHSEC_ENFORCE=0 to explicitly disable.

Affected package ranges reported by GitHub: nltk: <= 3.9.4

Scores and how they were measured

CVSS base severity

8.7

Version 4.0As of

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

Measurement source (opens a new tab)

How bad it is if exploited. Not a prediction of exploitation or proof you are exposed.

EPSS probability

Not available

A model's estimate of exploitation in the next 30 days, not certainty or your own risk.

Related technology

Sources

  1. Primary source

    GitHub-reviewed advisory GHSA-p3m8-78j2-g5p3 (opens a new tab)

    The public advisory supplies the description, affected package/version ranges, and any listed CVSS metric. GitHub review is not local review.

    Published Checked

  2. Primary source

    GitHub public advisory API page (opens a new tab)

    The API page supplied GHSA-p3m8-78j2-g5p3, its actual identifiers, source dates, and structured metrics.

    Published Date not suppliedChecked

Cite this record

For factual claims, cite the primary sources above; cite KEVWire for its compilation, dates, and classifications.

APA

KEVWire. (2026, October 27). NLTK: Default ENFORCE=False Disables All pathsec Security Controls (CVE-2026-62388). https://kevwire.com/record/CVE-2026-62388

MLA

"NLTK: Default ENFORCE=False Disables All pathsec Security Controls (CVE-2026-62388)." KEVWire, 27 Oct. 2026, kevwire.com/record/CVE-2026-62388.

Chicago

KEVWire. "NLTK: Default ENFORCE=False Disables All pathsec Security Controls (CVE-2026-62388)." Last modified October 27, 2026. https://kevwire.com/record/CVE-2026-62388.

Evidence summary (plain text)

NLTK: Default ENFORCE=False Disables All pathsec Security Controls (Sep 2, 2026).
NLTK's pathsec.py security module defaults to ENFORCE=False (line 24), which means all 8 security validation functions only emit RuntimeWarning instead of raising exceptions when violations are detected.

The pathsec module was introduced as the fix for CVE-2024-39705 (arbitrary code execution via pickle) and CVE-2026-0846 (path traversal). However, with ENFORCE=False as the default:
CVSS 8.7 (version 4.0; evidence as of Oct 27, 2026; https://github.com/advisories/GHSA-p3m8-78j2-g5p3).
Sources:
GitHub-reviewed advisory GHSA-p3m8-78j2-g5p3: https://github.com/advisories/GHSA-p3m8-78j2-g5p3
GitHub public advisory API page: https://api.github.com/advisories?type=reviewed&per_page=100&sort=updated&direction=desc
Record ID: CVE-2026-62388.
Record origin: Ingested record.
AI evidence: Not assessed.
Known exploitation: Not assessed.
Zero-day status: Not assessed. KEV membership alone does not establish zero-day status.
About this data

This record was ingested from a data source. Retrieved: Oct 27, 2026, 11:45 UTC. Ingestion is not an independent editorial investigation.

A CISA KEV listing documents known exploitation, not necessarily a zero-day; absence from the catalog does not prove a vulnerability has never been exploited.

Technology tags indicate possible relevance, not verified exposure. Confirm the affected product, version, and configuration against your own inventory; KEVWire does not scan your systems.

A personal reading checklist on this device, not verified remediation.

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