Skip to content
Noroxi
CVE-2026-0847· NVD / CVE Program· CNA @huntr_ai

Path Traversal in nltk/nltk

A vulnerability in NLTK versions up to and including 3.9.2 allows arbitrary file read via path traversal in multiple CorpusReader classes, including WordListCorpusReader, TaggedCorpusReader, and BracketParseCorpusReader. These classes fail to properly sanitize or validate file paths, enabling attackers to traverse directories and access sensitive files on the server. This issue is particularly critical in scenarios where user-controlled file inputs are processed, such as in machine learning APIs, chatbots, or NLP pipelines. Exploitation of this vulnerability can lead to unauthorized access to sensitive files, including system files, SSH private keys, and API tokens, and may potentially escalate to remote code execution when combined with other vulnerabilities.

HighCVSS 7.5 · v3.1—Proof of concept Fix available
Published
Mar 4, 2026
Updated
Sep 16, 2026
EPSS
0.9% · 59th percentile
Follow this CVE

Sign in to follow · You’ll be notified if a followed record enters KEV, gets an exploit or is updated.

Report tools

JSON

Action score

30

Monitor

Low priority for now.

CVSS
30 / 40 · 7.5 / 10
CISA KEV
0 / 30 · Not listed
EPSS
0 / 30 · 0.9%

CISA SSVC decision

Exploitation
proof of concept
Automatable
yes
Technical impact
partial

Vulnrichment: CISA's decision-tree inputs.

CNA vs NVD score

NVD
7.5
CNA · @huntr_ai
8.6
1.1 point gap

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

The score given by the assigning authority versus NVD’s independent score. A gap means the severity is contested.

Noroxi analysis

No Noroxi analysis for this record yet

We don't hand-write analysis for the hundreds of thousands of vulnerabilities in the database; that wouldn't be honest. For notable, high-impact vulnerabilities our team writes the mechanism, detection and remediation steps.

We use this product, ask for help

Affected systems

VendorProduct
nltknltk

Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

  • nltk nltkup to 3.9.2 inclusive

Versions reported by the vendor

Affected version ranges reported by the assigning authority (@huntr_ai). Independent of NVD's CPE analysis and usually ahead of it.

  • nltk nltk/nltk

    • unspecified and later · up to and including latestaffected

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

EcosystemPackageAffected rangeFix
Debian:12nltkall versions—
Debian:14nltkbefore 3.9.3-13.9.3-1
openSUSE:Tumbleweedpython-nltkbefore 3.9.3-1.13.9.3-1.1
PyPInltkup to and including 3.9.2—
PyPInltkbefore 3.9.33.9.3

Same product

nltk: all records

Other highest-scoring records for the same primary product.

  • CVE-2026-0848Arbitrary Code Execution in NLTK StanfordSegmenter via Untrusted JAR Loading
    40Plan
  • CVE-2026-79675NLTK before 3.10.3 JVM Argument Injection via Per-Call Options
    37Monitor
  • CVE-2026-79657NLTK before 3.10.3 Remote Code Execution via Unsafe Pickle Deserialization
    37Monitor
  • CVE-2026-78683NLTK before 3.10.0 Remote Code Execution via Unsafe Pickle Deserialization
    37Monitor
  • CVE-2026-79674NLTK 3.10.2 Path Traversal via corpus-reader constructors
    35Monitor
  • CVE-2025-14009Zip Slip Vulnerability in nltk/nltk Leading to Remote Code Execution
    35Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / packageFixed versionSource
debian:nltk3.9.3-1 · Debian:14Package registry (OSV)
opensuse:python-nltk3.9.3-1.1 · openSUSE:TumbleweedPackage registry (OSV)
PyPI:nltk3.9.3Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

  • Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
SourceKindDate
Proof-of-concept repository on GitHubstars:02026-03-29

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

  1. Published
  2. First PoC+24 d
  3. TodayOct 8, 2026+218 d
EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

No credits in the CNA record.

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

  • CVE-2026-62384171 days apartNLTK FramenetCorpusReader Symlink Sandbox Bypass before 3.10.2
    34Monitor
  • CVE-2026-63312171 days apartNLTK StreamBackedCorpusView Bypasses pathsec.ENFORCE Arbitrary File Read
    34Monitor
  • CVE-2026-3323616 days apartNLTK has a Downloader Path Traversal Vulnerability (AFO) - Arbitrary File Overwrite
    32Monitor
  • CVE-2026-79676174 days apartNLTK before 3.10.3 Path Traversal via Symlink Bypass
    32Monitor
  • CVE-2026-54293110 days apartNLTK: URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read
    30Monitor
  • CVE-2026-62383171 days apartnltk IPIPANCorpusReader Symlink Arbitrary File Read
    27Monitor

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

Technical details

Attack conditions

  • Anyone who can reach it over the internet can trigger it.
  • No account or password is required.
  • No user action is required.
  • No special conditions are required; it is repeatable.

If successful

Confidentiality
high · data can be read
Integrity
none
Availability
none
Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality impact
High
Integrity impact
None
Availability impact
None

Weakness class (CWE)

CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

nvd-primary

Root cause

A user-supplied file name is joined with the allowed directory, but the result is never checked to confirm it is still inside that directory.

The bug in code

The whole CWE-22 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

ts
const file = path.join(ROOT, req.query.name);res.sendFile(file);

Fixed

ts
const file = path.resolve(ROOT, req.query.name);if (!file.startsWith(ROOT + path.sep)) {  return res.sendStatus(400);}res.sendFile(file);

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

ATT&CK techniques

—

Change log

  1. Fix✗ → ✓

For records you follow, these changes also arrive as notifications. →

References

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records