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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

NLTK’s WordNet Browser can be shut down by anyone able to reach its HTTP server. No login or user interaction is required. The impact is service interruption rather than data theft or modification. Risk is concentrated in systems that run this optional browser and expose it beyond trusted users.

Executive priority

Prioritize prompt remediation for reachable WordNet Browser instances because an unauthenticated attacker can stop the service repeatedly. Lower the urgency for installations where the component is not running, but confirm that status through inventory. This is primarily an availability and operational-resilience issue, not a disclosed confidentiality or integrity compromise.

Technical view

NLTK 3.9.3 and earlier contain an unauthenticated shutdown handler in nltk.app.wordnet_app. A crafted HTTP GET request invokes immediate process termination through os._exit(0). The CVSS 3.1 score is 7.5, reflecting network-accessible, low-complexity denial of service with high availability impact. Commit bbaae83db86a0f49e00f5b0db44a7254c268de9b patches the flaw.

Likely exposure

Exposure requires the WordNet Browser HTTP server to be running and reachable by an attacker. Internet-facing, shared-network, containerized, or remotely accessible development instances warrant attention. Systems merely installing NLTK without running nltk.app.wordnet_app are not shown by the supplied evidence to be directly exploitable.

Exploitation context

The request is simple, unauthenticated, and requires no user interaction, making repeated denial of service plausible where the server is reachable. The supplied record says CVE-2026-33231 is not in KEV, and no provided source establishes active exploitation. Treat exploit activity as unconfirmed.

Researcher notes

The issue maps to CWE-306 because a safety-critical shutdown action lacks authentication. The cited implementation terminates the process immediately, supporting the high availability rating. Scope appears limited to the WordNet Browser server, not all NLTK functionality. The bundle identifies the patch commit but does not identify a specific fixed NLTK release.

Mitigation direction

  • Upgrade to a vendor release that incorporates commit bbaae83db86a0f49e00f5b0db44a7254c268de9b.
  • Consult the NLTK advisory for confirmed fixed-version availability before deployment.
  • Disable the WordNet Browser where it is unnecessary.
  • Restrict the browser listener to trusted hosts or networks until patched.
  • Review applicable Red Hat advisories when using affected Red Hat packages.

Validation and detection

  • Inventory NLTK versions and identify installations at version 3.9.3 or earlier.
  • Confirm whether nltk.app.wordnet_app is started in any environment.
  • Review listener configuration and network controls without sending the shutdown request.
  • Verify the installed package contains the cited patch commit or a vendor-confirmed equivalent.
  • Check HTTP and process logs for unexpected browser termination or restart patterns.
Prepared
Confidence
high
Sources
5

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-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
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
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.

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