NLTK: URL-Encoded Path Traversal in nltk.data.load() Allows Arbitrary Local File Read
nltk · nltk
Official source article: GitHub GHSA-P4GQ-832X-FM9V ↗. Check the applicable product and release in the original source.
7.5HighCVSS 3.1
Recommended action
Patch only the product branches with a verified fix
High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Published severityHigh→Operational priority:Critical, raised one band.upgradedsince 9 Sep 2026
Evidence used
No CISA KEV confirmation is currently recorded.
A structured source references public exploit or proof-of-concept material.
The selected CVSS metric records a network-reachable, unauthenticated path with no user interaction.
EPSS is 0.63% for the current model date.
Compensating controls
Validate the affected product branch and deploy the verified fixed release.
Restrict the affected network interface to trusted sources where business-safe.
Increase monitoring for the attack path and post-exploitation behaviour described in the report.
Verification
Confirm that the asset runs nltk nltk and falls inside the recorded affected range.
Verify the installed build against the product-specific fixed version after deployment.
Validate exposure, authentication requirements and compensating controls in the actual environment.
Reopen this reassessment when CVSS, KEV, EPSS, exploit evidence or remediation changes.
Cross-source reconciliation
Remediation availability differs by product scope
Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Debian Security Tracker: 2 affected package states with no published fix
Distribution package intelligence
Release-specific package status
Debian, ubuntu findings are scoped to the named distribution, release and source package. An absent finding does not mean a package is unaffected.
5 package states
Package result overrides the generic status
BlackTree has verified remediation for at least one product or source, but the relevant distribution still reports no fixed package for 2 affected package states shown here. Treat those rows as affected with no fix until that distribution publishes a fixed version.
Repository candidate not checked
A published vendor fix does not prove that a matching update is enabled and installable on a particular asset. Confirm the local package candidate before scheduling remediation.
Distribution release
Source package
Vendor state
Fixed version
Evidence
Debian trixietrixie · source
nltk
Affected, no fix publishedDebian currently tracks this release as open.
These OSV and GitHub advisory ranges apply only to the named package and ecosystem. A listed fixed version is not a universal product patch or proof that an update is installed.
Structured product status and remediation from the issuing vendor. Product-state explanations are always visible; large lists can be searched or downloaded.
1 current
CVE-2026-54293 · CSAF 2.0 · revision 3 · finalRed Hat Product Securitynltk: NLTK: Information Disclosure via Path Traversal in `nltk.data.load()`
4 known affected
The vendor explicitly identifies these products as affected by this CVE.
exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 as a component of Exploit Intelligence
ansible-automation-platform-25/lightspeed-chatbot-rhel8 as a component of Red Hat Ansible Automation Platform 2
rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI)
Summary
A flaw was found in NLTK (Natural Language Toolkit). The `nltk.data.load()` function is vulnerable to path traversal when processing specially crafted `nltk:` URLs. An attacker can exploit a decode-after-check flaw, where URL-encoded path separators and traversal segments bypass security checks. This allows the attacker to read arbitrary files from the filesystem, leading to information disclosure.
Remediation
For Red Hat OpenShift AI 2.25.9 see the following documentation, which will be updated shortly for this release, for important instructions on how to upgrade your cluster and fully apply this errata update: https://docs.redhat.com/en/documentation/red_hat_openshift_ai/
Optional official sources
National CERT insights ?CERT means Computer Emergency Response Team; CSIRT is the closely related term Computer Security Incident Response Team.
Choose official national sources for this report. Each advisory shows its original language. Your selection is remembered on this device and included in shared links.
Official European source
ENISA European Vulnerability Database
Official EUVD identifiers, advisory evidence and known-exploited context. Missing fields are not treated as evidence of low risk.
1 current
ENISA EUVD identifier
EUVD-2026-38333
No EUVD known-exploited evidence
NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.
EUVD state
Present in the current official mapping
Known exploitation
Not present in the current ENISA EUVD known-exploited dataset. This is not proof of no exploitation.
ENISA score
7.5 · CVSS 3.1
Advisory evidence
No linked advisory details stored yet
Recommended actionPatch only the product branches with a verified fix
High technical severity with public exploit material referenced by a structured source; prioritise exposed affected systems while verifying vendor guidance. Verified remediation exists for at least one product or source, but 2 structured product or package states remain unresolved. Apply remediation only to the exact product branch confirmed by its source.
Fix availability varies by product
01
What, why and how
NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.
What
NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.
Why
Attacker-controlled path data is not constrained to the intended directory before the application accesses a file.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may obtain information outside the intended access boundary.
What
NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.
Why
Attacker-controlled path data is not constrained to the intended directory before the application accesses a file.
How
An attacker operating through a network path may attempt exploitation without authentication or user interaction. If successful, the issue may obtain information outside the intended access boundary.
02
Exploit reality and attack path
CVSS severity, EPSS forecast probability, public exploit material and CISA-confirmed exploitation are separate signals.
Observed exploitation ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.No confirmed evidence
No CISA KEV match was present at the last successful refresh. This means no confirmation from that source, not proof of no exploitation.
Public PoC / exploit material ?Confirmed exploitation and public exploit material are separate signals. Attacks can occur without public proof-of-concept or exploit code.Reference recorded
A structured CVE source labels at least one public reference as exploit material. BlackTree has not independently validated that it is safe, reliable or weaponised.
Likely attack path
a network path → Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal') → obtain information outside the intended access boundary
Attack surface
Network
Privileges required
None: unauthenticated exploitation is possible
User interaction
None
Attack complexity
Low: no specialised conditions are recorded
Security boundary
Unchanged: impact remains within the vulnerable component's security authority
Weakness ?CWE means Common Weakness Enumeration: a standard category for the underlying weakness.
CWE-22: Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal'). 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.
CVSS vector ?CVSS means Common Vulnerability Scoring System. The vector records the metric values used to calculate technical severity.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
Common Vulnerability Scoring System 3.1: the compact vector below is decoded into plain language.
AVNetworkAttack vector: The vulnerable component can be reached over a network.ACLowAttack complexity: No specialised conditions are required beyond attacker-controlled input.PRNonePrivileges required: The attacker does not need an account or existing privileges.UINoneUser interaction: No action by another user is required.SUnchangedScope: The security impact remains within the vulnerable component's authority.CHighConfidentiality impact: A successful attack can cause a major loss.INoneIntegrity impact: No direct loss is represented by this metric.ANoneAvailability impact: No direct loss is represented by this metric.
Post-exploitation / living off the land
No specific living-off-the-land technique is confirmed in the structured sources. Monitor normal administration tools for activity inconsistent with the affected service's baseline.
Only matched European and national findings are included. Language selectors and unavailable sources are omitted.
ENISA EUVD · EUVD-2026-38333Official EUVD mapping
NLTK (Natural Language Toolkit) is a suite of open source Python modules, data sets, and tutorials supporting research and development in Natural Language Processing. Prior to 3.10.0-rc1, nltk.data.load() in NLTK is vulnerable to path traversal via URL-encoded path separators and traversal segments when using the nltk: URL scheme. The unsafe-path regex check is performed before url2pathname() decodes the %xx sequences (a classic decode-after-check / TOCTOU-style flaw), allowing an attacker to bypass the protection documented in NLTK's SECURITY.md and read arbitrary files from the filesystem. While literal traversal strings such as ../../../etc/passwd are correctly blocked, encoded variants such as %2fetc%2fpasswd, %2e%2e%2f..., and ..%2f..%2f slip past the regex and are subsequently decoded into a real filesystem path. This vulnerability is fixed in 3.10.0-rc1.
Official EUVD record ↗Cyber Security Agency of Singapore · English · CSA-SB-20260624Security Bulletin 24 June 2026
The Cyber Security Agency of Singapore included this CVE in its official Security Bulletin 24 June 2026, published on 24 June 2026. Open the linked bulletin for the product, severity and reference information published in that issue.
Official advisory ↗CERT-FR · French · CERTFR-2026-AVI-1206Multiples vulnérabilités dans les produits IBM
Official advisory ↗JVN iPedia · Japanese · JVNDB-2026-021249NLTKにおけるパストラバーサルの脆弱性
NLTK(Natural Language Toolkit)は、自然言語処理の研究開発を支援するオープンソースのPythonモジュール、データセット、およびチュートリアルのスイートです。3.10.0-rc1より前のバージョンでは、NLTKのnltk.data.load()がnltk: URLスキームを使用する際に、URLエンコードされたパス区切り文字やトラバーサルセグメントによるパストラバーサルの脆弱性を持っていました。不安全なパスの正規表現チェックは、url2pathname()が%xxシーケンスをデコードする前に行われており(典型的なデコード後のチェック/TOCTOUスタイルの欠陥)、攻撃者がNLTKのSECURITY.mdに記載された保護を回避し、任意のファイルをファイルシステムから読み取ることを可能にしていました。../../../etc/passwdのようなリテラルトラバーサル文字列は正しくブロックされますが、%2fetc%2fpasswd、%2e%2e%2f...、および..%2f..%2fのようなエンコード変種は正規表現をすり抜け、実際のファイルシステムパスにデコードされます。この脆弱性は3.10.0-rc1で修正されました。
Operational remediation based on structured source evidence.
Status ?Patch availability is based on structured fixed-version fields and authoritative update references. If no fix is verified, check the vendor advisory before making a change.
Use the product-specific evidence above. Patch only products with a verified fixed release, and keep every affected or under-investigation state without a matching fix in the remediation queue.
Workaround
No verified workaround is recorded. If business-safe, reduce exposure to the affected interface and allow only trusted sources until authoritative guidance is available.
04
Evidence and provenance
Published 22 Jun 2026 · Last source change 9 Sept 2026, 12:04 UTC · CWE-22 · Improper Limitation of a Pathname to a Restricted Directory ('Path Traversal')
CVE recordCVE.org · 5.2
CVSS sourceCNA
EPSS source ?The date BlackTree first stored a score for this CVE from the daily FIRST EPSS feed.FIRST · tracked since 2026-08-14
European sourceENISA EUVD · EUVD-2026-38333
Product sourceVendor CSAF · Red Hat Product Security
Remediation sourceVendor CSAF · Red Hat Product Security
CWE sourceCNA
NVD statusNVD modified after enrichment
Core structured fields are present and their contributing authorities are shown above.
Affected versionsThe structured affected or fixed version information changed.
Before
exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 as a component of Exploit Intelligence; ansible-automation-platform-25/lightspeed-chatbot-rhel8 as a component of Red Hat Ansible Automation Platform 2; rhoai/odh-ta-lmes-job-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI) · Fixed: registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:513923c7b5f7dcfb80be58476429560ea167f7ef95e5f92add823602508643ae_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:c2c09ca156aa93f4c435de49bfdce6bf31530515cc77b1b2e0020f34551c5cae_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:1458d874cda368ba9e4eda79bc4d9414529a695f361dad677504791824e0f209_arm64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:4d89196e9a333993dbb01199c418a0e3e77f32e16690a4067ef10466c2e7cb03_amd64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:c3c162453715ed81289a4ed0b09544b7c7ea31d6a2b718c6f18c27f525bcd53b_ppc64le as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9@sha256:70e0fb79848b7aa369a969ff2a2b784cee865799c09ef105d2c340ebc8e10478_amd64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:17acd0102ff081f059f4f2740b2fcb46a0899df6996f5d61f8919a197b474332_ppc64le as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:346b46cd6e359f0843ca87ac4645638ba3367690907fc4a112b0877c89daa897_arm64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:41c9b77bd5acaaaf59c87ae4ba90e5bbf320691a74fd993b1e7af668a871935e_amd64 as a component of Red Hat OpenShift AI 3.4
After
exploit-intelligence-tech-preview/vulnerability-analysis-rhel9 as a component of Exploit Intelligence; ansible-automation-platform-25/lightspeed-chatbot-rhel8 as a component of Red Hat Ansible Automation Platform 2; rhoai/odh-trustyai-garak-lls-provider-dsp-rhel9 as a component of Red Hat OpenShift AI (RHOAI); rhoai/odh-workbench-jupyter-pytorch-llmcompressor-cuda-py312-rhel9 as a component of Red Hat OpenShift AI (RHOAI) · Fixed: registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:513923c7b5f7dcfb80be58476429560ea167f7ef95e5f92add823602508643ae_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:c2c09ca156aa93f4c435de49bfdce6bf31530515cc77b1b2e0020f34551c5cae_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:12b22139069ac4f0679722c3020ae2ce5aa915d6aedd3837eb6a155e642acad0_ppc64le as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:26d9256029f78df1b0d16a5d388d6caece5ad0c0639a76a99dbcc9f32c281002_amd64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:429eee0ace6becaae1c63774098bce8df3c9e92a6d4bdc33cd2256dcec918025_arm64 as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-ta-lmes-job-rhel9@sha256:ad7cc622e887ceffb195db5188e224a8c4bb1b52711eec195edadba77673c93f_s390x as a component of Red Hat OpenShift AI 2.25; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:1458d874cda368ba9e4eda79bc4d9414529a695f361dad677504791824e0f209_arm64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:4d89196e9a333993dbb01199c418a0e3e77f32e16690a4067ef10466c2e7cb03_amd64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-llama-stack-core-rhel9@sha256:c3c162453715ed81289a4ed0b09544b7c7ea31d6a2b718c6f18c27f525bcd53b_ppc64le as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-pipeline-runtime-pytorch-llmcompressor-cuda-py312-rhel9@sha256:70e0fb79848b7aa369a969ff2a2b784cee865799c09ef105d2c340ebc8e10478_amd64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:17acd0102ff081f059f4f2740b2fcb46a0899df6996f5d61f8919a197b474332_ppc64le as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:346b46cd6e359f0843ca87ac4645638ba3367690907fc4a112b0877c89daa897_arm64 as a component of Red Hat OpenShift AI 3.4; registry.redhat.io/rhoai/odh-trustyai-nemo-guardrails-server-rhel9@sha256:41c9b77bd5acaaaf59c87ae4ba90e5bbf320691a74fd993b1e7af668a871935e_amd64 as a component of Red Hat OpenShift AI 3.4
Affected versionsThe structured affected or fixed version information changed.
Before
< 3.10.0-rc1 · Fixed: An authoritative update reference is available, but the fixed version is not recorded in the structured CVE fields. Check the linked vendor advisory for the applicable release.
After
nltk: < 3.10.0-rc1 · Fixed: RHSA-2026:42644: Red Hat OpenShift AI 2.25
Technical terms and abbreviations used in this report
CVE
Common Vulnerabilities and Exposures: the public identifier for one disclosed vulnerability.
CVSS
Common Vulnerability Scoring System: a technical severity framework; it is not patching priority by itself.
EPSS
Exploit Prediction Scoring System: FIRST's estimate of the probability that exploitation activity will be observed in the next 30 days; it is a forecast, not confirmation.
CWE
Common Weakness Enumeration: the standard category describing the underlying software or hardware weakness.
CNA
CVE Numbering Authority: an organisation authorised to assign and publish CVE records.
CISA ADP
Cybersecurity and Infrastructure Security Agency Authorized Data Publisher: structured enrichment added to a CVE record.
NVD
National Vulnerability Database: NIST's enrichment service for CVE records.
CERT / CSIRT
A computer security incident response team that publishes warnings or coordinates incident response.
PoC
Proof of concept: public material that demonstrates or helps reproduce exploitation.
CSAF
Common Security Advisory Framework: a machine-readable format for security advisories.
LoTL
Living off the land: abuse of legitimate tools or system functions during an attack.