CVE-2026-0846 - A vulnerability in the filestring() function of the nltk.util module in nltk version 3.9.2 allows arbitrar

CVE-2026-0846 + A vulnerability in the filestring() function of the nltk.util module in nltk version 3.9.2 allows arbitrar + High + 2026-03-09

One-sentence business risk

Filesystem escape can disclose secrets or overwrite trusted files, turning a dependency bug into host or account compromise.

Research notes

  • Root cause: A vulnerability in the filestring() function of the nltk.util module in nltk version 3.9.2 allows arbitrary file read due to improper validation of input paths.
  • Affected versions: Affected versions named by the upstream advisory and dependency metadata.
  • Fixed / safe versions: version 3.9.2 allows arbitrary file read due to improper validation.
  • Public exploit / PoC signal: the consulted NVD/GHSA/vendor sources describe the trigger class; treat it as reproducible until patched.
  • CVSS: 7.5 CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N.

Exact vulnerable code pattern

target = join(base_dir, user_path); read_or_write(target)

Fixed / mitigated code pattern

target = realpath(join(base_dir, user_path)); assert target is inside realpath(base_dir)

Dependency or runtime update:

rg -n "affected component|CVE-2026-0846" .
# update affected runtime/product to version 3.9.2 allows arbitrary file read due to improper validation

Step-by-step integration guide

  1. Inventory affected component across source, lockfiles, SBOMs, container images, CI images, and deployment manifests.
  2. Upgrade to version 3.9.2 allows arbitrary file read due to improper validation or apply the exact vendor patch referenced below.
  3. Replace the vulnerable path-traversal pattern with the fixed pattern and fail closed on malformed input.
  4. Add a regression test that exercises the advisory trigger and proves the request is rejected, bounded, or authorized.
  5. Deploy through canary, monitor security logs and resource metrics, then remove temporary edge blocks only after all runtimes are fixed.

Alternative mitigations

  • Disable the vulnerable feature path while the package/runtime update rolls out.
  • Add WAF or reverse-proxy rules for traversal tokens, prototype-polluting keys, oversized frames, shell metacharacters, or unauthenticated tool calls matching the trigger class.
  • Restrict internal egress, rotate exposed secrets, and revoke affected tokens/keys if the vulnerability can disclose config, logs, JWT secrets, proxy credentials, or PKI material.
  • For admin/API authorization issues, temporarily require elevated roles and explicit ownership checks at the gateway.

Detection signature

id: cve-2026-0846-a-vulnerability-in-the-filestring-function-of-th
source: NVD
dependency_or_product: "affected component"
affected: "Affected versions named by the upstream advisory and dependency metadata"
fixed: "version 3.9.2 allows arbitrary file read due to improper validation"
signals:
  - "path-traversal"
  - "../"
  - "__proto__"
  - "tools/call"
  - "wp_ajax_nopriv"
  - "pickle.loads"
  - "shell command construction"
action: "upgrade, add regression test, and verify deploy artifact"

Copy-paste skill

You are remediating CVE-2026-0846 (A vulnerability in the filestring() function of the nltk.util module in nltk version 3.9.2 allows arbitrar) in this repository.

Find every affected dependency, runtime, image, service configuration, and reachable code path. Upgrade or patch to version 3.9.2 allows arbitrary file read due to improper validation. Replace the vulnerable path-traversal pattern with a fail-closed implementation, add a regression test for the trigger shape, and update deployment/SBOM artifacts. If this repository does not control the affected runtime, create TRIAGE.md naming the owner, affected version, fixed version, and blocking decision.

Keywords, affected tech stack, and revenue tags

  • Keywords: CVE-2026-0846, path-traversal, affected component, NVD.
  • Affected tech stack: general.
  • Revenue tags: sellable_to_fintech, enterprise_blocker, high_priority_sla.

References