| Package | Affected versions | Patched versions |
|---|---|---|
| nltk | < 3.10.0 | 3.10.0 |
| nltk | < 3.10.0 | 3.10.0 |
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:
Every security gate follows the same pattern:
ENFORCE = os.environ.get('NLTK_PATHSEC_ENFORCE', '').lower() in ('1', 'true', 'yes')
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:
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.
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