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CVE Record

CVE-2026-33231: NLTK has unauthenticated remote shutdown in nltk.app.wordnet_app

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, `nltk.app.wordnet_app` allows unauthenticated remote shutdown of the local WordNet Browser HTTP server when it is started in its default mode. A simple `GET /SHUTDOWN%20THE%20SERVER` request causes the process to terminate immediately via `os._exit(0)`, resulting in a denial of service. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the issue.

HighCVSS 7.5Not KEV-listedUpdated
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Glexia's TakeAutomated analysishigh

Security readout for executives and security teams

Plain-English summary

This issue lets anyone who can reach NLTK's local WordNet Browser web server shut it down without logging in. The business impact is availability loss, not data theft. It matters most where research, NLP tooling, or internal services expose that browser over a network.

Executive priority

Treat as high priority where NLTK WordNet Browser is network-accessible, because unauthenticated users can cause service interruption. Lower priority for systems that only use NLTK as a library and never start the browser.

Technical view

NLTK versions 3.9.3 and earlier include an unauthenticated shutdown path in nltk.app.wordnet_app. A network request to the default WordNet Browser HTTP server can immediately terminate the process through os._exit(0), causing denial of service. The supplied sources identify CWE-306 and a patch commit.

Likely exposure

Exposure is likely limited to environments running NLTK <= 3.9.3 and starting nltk.app.wordnet_app with the WordNet Browser reachable by untrusted users. Standard NLTK library use without that browser is not shown as exposed by the supplied sources.

Exploitation context

The CVSS vector is network-reachable, low complexity, no privileges, and no user interaction, with high availability impact. The provided data says KEV is false, and no supplied source establishes active exploitation in the wild.

Researcher notes

The supplied evidence supports denial of service only. It does not support confidentiality or integrity impact, broad NLTK runtime compromise, or confirmed exploitation. Fixed release details are not present in the bundle beyond the upstream patch commit and Red Hat advisories.

Mitigation direction

  • Upgrade NLTK to a version containing commit bbaae83db86a0f49e00f5b0db44a7254c268de9b.
  • Review NLTK and Red Hat advisories for exact fixed package versions.
  • Restrict WordNet Browser access to trusted local users only.
  • Stop exposed WordNet Browser instances until patched.
  • Monitor affected systems for unexpected WordNet Browser process termination.

Validation and detection

  • Inventory Python environments for NLTK versions <= 3.9.3.
  • Identify systems starting nltk.app.wordnet_app or the WordNet Browser.
  • Check whether the browser HTTP server is reachable beyond localhost.
  • Verify patched builds include the referenced upstream commit.
  • Review Red Hat errata applicability for managed platform packages.
Prepared
Confidence
high
Sources
10

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

Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.

cwe · medium confidence lookup

CWE-306: Credential and account abuse lookup

Authentication and credential weaknesses can make valid-account abuse and credential telemetry useful review starting points. 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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cve · low confidence lookup

CVE-2026-33231 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
7.5 (3.1)
Known Exploited
No
Published

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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
9Source 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
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6GitHub_M
7.5CVSS 3.1HighCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H3.93.6redhat-SADP

Vulnerability scoring details

Base CVSS 3.1 score

7.5High
CVSS 3.1 vector shape for CVE-2026-33231Attack VectorAttack ComplexityPrivileges RequiredUser InteractionScopeConfidentiality ImpactIntegrity ImpactAvailability Impact

Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/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: Denial of Service via unauthenticated remote shutdown
other:Red Hat severity ratingcvssV3_1
  • 2026-03-20T23:02:37.298Z: Reported to Red Hat.
  • 2026-03-20T22:45:40.784Z: Made public.

Source materials

Affected products

Products and packages named in the record

VendorProductVersion / packageStatus
nltknltk<= 3.9.3Listed
Weakness

CWE details

CWE-306

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

CWE-306 · source CWE mapping

Missing Authentication for Critical Function

Missing Authentication for Critical Function represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.

Open CWE intelligenceSame-CWE CVEs