vulnerability / NVI-00016187 / Revision 1
Natural Language Toolkit (NLTK): URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read
GitHub lists this reviewed advisory for nltk. Published version ranges and source prerequisites are shown below; this is not an inspection of a visitor’s application.
This report has not inspected your inventory, configuration, deployed build, reachability or evidence. A catalog listing and a severity score do not establish exposure or compromise.
01 / Meaning
Why it matters
Published affected context helps an owner decide what evidence to gather. This report has not examined your application.
7.5 high
GitHub source severity; exploitability and local consequence require separate evidence.
As of · GitHub Advisory Database
02 / Applicability
The affected context
Affected versions, configuration prerequisites and known exclusions are public. Confirm each one against the deployed service.
nltk
source listed<= 3.9.4
### Summary nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. ### Affected Component nltk/data.py — find(), normalize_resource_url(), and the _UNSAFE_NO_PROTOCOL_RE regex check. Relevant occurrences: data.py L650–L653 — final path constructed from url2pathname(resource_name) after checks data.py L54–L69 — _UNSAFE_NO_PROTOCOL_RE operates only on the undecoded string data.py L219–L245 — normalize_resource_url() for nltk: scheme contributes to decode-after-check data.py L615–L618 — defense-in-depth traversal check also operates on undecoded input Root Cause The regex _UNSAFE_NO_PROTOCOL_RE is matched
03 / Response
What to do next
- investigate
Identify the exact component and deployed version, examine the linked publisher’s conditions, and retain evidence of any mitigation.
Confirm current vendor support, compatibility and deployment evidence. This report has not tested a fix in your system. GitHub Advisory Database
A fixed release is not deployment evidence.
Check current vendor support and compatibility. After making a change, verify the deployed build and relevant runtime conditions. Keep the evidence, owner and time. An updated lockfile alone does not prove what is running.
04 / Limits
What this report cannot establish
- Customer inventory, deployment, reachability and exploitation have not been inspected.
05 / Provenance
Sources you can inspect
Each assertion retains its source. Mirrored records may repeat one underlying publisher; additional links are not independent corroboration.
- GHSA-p4gq-832x-fm9v ↗
GitHub Advisory Database · vendor advisory
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Public revision history
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- Revision 1 ·
First indexed by Null; source disclosure date is shown separately.