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CVE Record

CVE-2026-33236: NLTK has a Downloader Path Traversal Vulnerability (AFO) - Arbitrary File Overwrite

NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. In versions 3.9.3 and prior, the NLTK downloader does not validate the `subdir` and `id` attributes when processing remote XML index files. Attackers can control a remote XML index server to provide malicious values containing path traversal sequences (such as `../`), which can lead to arbitrary directory creation, arbitrary file creation, and arbitrary file overwrite. Commit 89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a patches the issue.

HighCVSS 8.1Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

NLTK downloader can be tricked into writing files outside its intended data directory when it reads a malicious remote XML index. This can overwrite files on systems where a user or process downloads data from an attacker-controlled index. The issue is high risk for research, CI, and application environments that fetch NLTK data dynamically.

Executive priority

Prioritize remediation for environments that download NLP datasets during builds, notebooks, or runtime. Treat this as high urgency where remote indexes are configurable or data downloads occur automatically. It is less urgent where NLTK downloader use is absent or tightly controlled.

Technical view

Versions 3.9.3 and prior do not validate remote XML index `subdir` and `id` attributes. Path traversal values can cause arbitrary directory creation, file creation, and file overwrite. CVSS 8.1 reflects network reachability, low complexity, no privileges, required user interaction, and high integrity and availability impact.

Likely exposure

Exposure is most likely where Python environments use NLTK <= 3.9.3 and invoke the downloader against remote or custom index servers. Systems that never run the downloader, only use already-vendored data, or restrict indexes to trusted sources have lower practical exposure.

Exploitation context

The source bundle does not show CISA KEV listing or active exploitation. Exploitation requires the downloader to process a malicious remote XML index controlled by an attacker, so attacker influence over the index source is the key condition.

Researcher notes

The advisory identifies CWE-22 path traversal in downloader XML index handling. The bundle names a patch commit but does not identify a specific fixed release number. Public exploit status is not established by the provided sources, and KEV is false.

Mitigation direction

  • Upgrade NLTK to a version containing commit 89fe2ec2c6bae6e2e7a46dad65cc34231976ed8a.
  • Use only trusted NLTK data index sources and avoid attacker-controlled mirrors.
  • Review Red Hat errata if consuming NLTK through Red Hat packages.
  • If no patched package is available, follow vendor guidance before using the downloader.
  • Avoid dynamic NLTK data downloads in production until patched.

Validation and detection

  • Inventory Python environments for NLTK versions 3.9.3 and prior.
  • Identify code, notebooks, jobs, or CI steps that call the NLTK downloader.
  • Check whether downloader configuration can use remote or custom XML indexes.
  • Confirm installed packages include the referenced patch commit or vendor fix.
  • Review filesystem integrity where untrusted indexes may have been processed.
Prepared
Confidence
high
Sources
11

Public sources used

Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.

Potential ATT&CK relevance

Conservative CVE-to-ATT&CK context

These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.

ATT&CK lookup starting points

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cwe · medium confidence lookup

CWE-22: File access and web shell behavior lookup

File traversal and upload weaknesses can lead teams to review file, web shell, execution, and collection telemetry. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.

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description · low confidence lookup

File access behavior lookup

The CVE wording references file access or upload behavior, so file telemetry and web shell review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.

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cve · low confidence lookup

CVE-2026-33236 mapping review

Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.

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Vulnerability profileCVE Program record
Severity
High
CVSS
8.1 (3.1)
Known Exploited
No
Published

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

Official CVE source material

CNA and ADP enrichment extracted from CVE v5

These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.

2CVSS vectors
5Timeline events
2ADP providers
10Source links

SSVC decision data

CISA-ADPCISA Coordinator
Timestamp
Version
2.0.3
Exploitation: pocAutomatable: yesTechnical Impact: partial

CVSS vector scores

2 official scores

We collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.

ScoreVersionSeverityVectorExploitImpactSource
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H2.85.2GitHub_M
8.1CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:N/I:H/A:H2.85.2redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

8.1High
CVSS 3.1 vector shape for CVE-2026-33236Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

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

Attack Vector
NetworkAdjacentLocalPhysical
Attack Complexity
LowHigh
Privileges Required
NoneLowHigh
User Interaction
NoneRequired
Scope
ChangedUnchanged
Confidentiality Impact
HighLowNone
Integrity Impact
HighLowNone
Availability Impact
HighLowNone

Vulnerability timeline

Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.

  1. CVE reservedCVE Program

    The CVE ID was reserved by the assigning CNA.

  2. ADP timelineredhat-SADP

    Made public.

  3. CVE publishedCVE Program

    The CVE record was published.

  4. ADP timelineredhat-SADP

    Reported to Red Hat.

  5. CVE updatedCVE Program

    The CVE record metadata indicates this as the latest update time.

ADP provider summaries

CISA-ADPCISA ADP Vulnrichment
other:ssvc
redhat-SADPnltk: NLTK: Arbitrary file overwrite and creation via path traversal in XML index files
other:Red Hat severity ratingcvssV3_1
  • 2026-03-20T23:01:51.656Z: Reported to Red Hat.
  • 2026-03-20T22:47:10.308Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nltknltk<= 3.9.3Listed
Weakness

CWE details

CWE-22

CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.

CWE-22 · source CWE mapping

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')

Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

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