VulnerabilityPublished 4 Mar 2026Updated 4 Nov 2026

CVE-2026-0847: NLTK has a Path Traversal issue

Affects nltkSource GCVE Database

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Authoritative record:CVE-2026-0847· High 8.6

Not known to be exploited · CVSS 8.6 High : upgrade to 3.9.3 soon.

Data as of 4 Nov 2026, 04:28 UTC

CVSS 3.0 base score

8.6High

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

Patch: Available – fixed in 3.9.3

CVSS:3.0/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:L

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

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: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
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: Low: Performance is reduced or there are interruptions in resource availability. Even if repeated exploitation of the vulnerability is possible, the attacker does not have the ability to completely deny service to legitimate users. The resources in the impacted component are either partially available all of the time, or fully available only some of the time, but overall there is no direct, serious consequence to the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 4 Mar 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 3 Nov 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 nltk to 3.9.3.

Patches and advisories

Affected software

Product	Affected	Fixed in
PyPInltk	Affected <3.9.3	Fixed in 3.9.3

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

AI-suggested

A patch is available in NLTK version 3.9.3. Users and administrators should upgrade to this version to remediate the vulnerability. The Red Hat advisory confirms the availability of fixes and provides guidance for updating affected products. No additional mitigation steps are indicated beyond applying the official fix.

Description

NLTK versions up to and including 3.9.2 contain a path traversal vulnerability in multiple CorpusReader classes, allowing attackers to read arbitrary files on the server. This occurs due to improper sanitization of file paths in classes such as WordListCorpusReader, TaggedCorpusReader, and BracketParseCorpusReader. Exploitation can lead to unauthorized access to sensitive files and potentially escalate to remote code execution when combined with other vulnerabilities. A fix is available in version 3.9.3.

Impact

The vulnerability allows unauthorized file read access via path traversal, potentially exposing sensitive system files, SSH private keys, and API tokens. This can compromise confidentiality and integrity, and may lead to remote code execution when combined with other vulnerabilities. The CVSS score of 8.6 reflects a high impact with network attack vector, low attack complexity, no privileges required, no user interaction, and high confidentiality and availability impact.

Summary

CVE-2026-0847 is a path traversal vulnerability affecting NLTK versions prior to 3.9.3. The flaw exists in multiple CorpusReader classes that do not properly validate or sanitize file paths, enabling attackers to traverse directories and read arbitrary files on the server. This vulnerability is critical in environments processing user-controlled file inputs, such as machine learning APIs or NLP pipelines. Exploitation can expose sensitive data including system files, SSH keys, and API tokens, and may lead to remote code execution if chained with other vulnerabilities. The issue is tracked under CWE-22 and has a CVSS 3.0 score of 8.6 (high severity). The vulnerability is fixed in NLTK version 3.9.3. Red Hat has issued advisories addressing this vulnerability in their products.

CWE-22Improper Limitation of a Pathname to a Restricted Directory (Path Traversal) (opens in a new tab)
Base weaknessLikelihood of exploit: HighCWE Top 25 (2025): #6OWASP Top 10 A01:2025: Broken Access Control (opens in a new tab)
The product uses external input to construct a pathname that is intended to identify a file or directory that is located underneath a restricted parent directory, but the product does not properly neutralize special elements within the pathname that can cause the pathname to resolve to a location that is outside of the restricted directory.
Implementation · Input Validation
Assume all input is malicious. Use an "accept known good" input validation strategy, i.e., use a list of acceptable inputs that strictly conform to specifications. Reject any input that does not strictly conform to specifications, or transform it into something that does.
Architecture and Design
For any security checks that are performed on the client side, ensure that these checks are duplicated on the server side, in order to avoid CWE-602. Attackers can bypass the client-side checks by modifying values after the checks have been performed, or by changing the client to remove the client-side checks…
Implementation · Input Validation
Inputs should be decoded and canonicalized to the application's current internal representation before being validated (CWE-180). Make sure that the application does not decode the same input twice (CWE-174).
OWASP Cheat Sheets
Authorization (opens in a new tab)
OWASP ASVS 4.0.3
V12.3.1 (opens in a new tab)
Attack patterns
Path Traversal (opens in a new tab)
Using Slashes and URL Encoding Combined to Bypass Validation Logic (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
Using Escaped Slashes in Alternate Encoding (opens in a new tab)
Using Slashes in Alternate Encoding (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Patches and advisories

Affected software

Description

AI analysisMachine-generated, updated 4 Nov 2026, 04:28 UTC

Public exploits and detectionGitHub proofs of concept

WeaknessesCWE-22

Technical details

References

Community reviews

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