VULNpocalypse

CVE-2026-21877

Advisory generated from the CVE record, CISA, Exploit Observer and VEDAS: what it is, whether it is exploited, who is affected, and how to fix and detect it.

Generated by VEDAS. Scores as of 2026-11-01 19:19 UTC. Rebuilt every few hours from cve-scores, CISA KEV and vedas-signatures. How this works and its limits.

What it is

The CVE record is reserved but not yet published on CVE.org, so affected versions, CVSS and references will appear here once it is.

How it can be exploited

Public exploit evidence (Exploit Observer)

Exploit Observer evidence for this CVE has not been fetched yet.

Live scores

EPSS
0.054
some chance of attack soon
VEDAS
0.982
strong exploit evidence
On CISA KEV
Not listed
Detection rule
Nuclei · Suricata

Who is affected

The CVE record does not list affected products yet.

How to fix it

No fixed version or vendor advisory is listed in the CVE record yet. Watch the vendor’s security page.

How to detect it

Nuclei template (active check)

N8n - Arbitrary File Upload

n8n is an open source workflow automation platform. In versions 0.121.2 and below, an authenticated attacker may be able to execute malicious code using the n8n service.

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

The template sends 1 request (GET /signin); it decides using dsl, regex, status, word matchers. Severity in the template: critical. Marked as not yet verified against a live vulnerable target.

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

bash
nuclei -u https://your-host -t CVE-2026-21877.yaml
Show the template (59 lines)
yaml
id: CVE-2026-21877

info:
  name: "N8n - Arbitrary File Upload"
  author: vedas-arpsyndicate
  severity: critical
  description: |
    n8n is an open source workflow automation platform. In versions 0.121.2 and below, an authenticated attacker
    may be able to execute malicious code using the n8n service.
  reference:
    - https://www.exploit.observer/?keyword=CVE-2026-21877&match=exact
    - https://subdomain.center/?engine=ammonites&keyword=n8n&match=exact
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
    cvss-score: 9.9
    cve-id: CVE-2026-21877
    cwe-id: CWE-434
  metadata:
    verified: false
  tags: cve,cve2026,n8n,workflow,rce,authenticated,passive,vuln
http:
  - method: GET
    path:
      - "{{BaseURL}}/signin"

    matchers-condition: and
    matchers:
      - type: word
        part: body
        words:
          - "<title>n8n.io"
        case-insensitive: true

      - type: dsl
        name: vulnerable
        dsl:
          - compare_versions(version, '>= 0.123.0', '< 1.121.3')

      - type: status
        status:
          - 200

    extractors:
      - type: regex
        name: base64_content
        group: 1
        regex:
          - '<meta name="n8n:config:sentry" content="([A-Za-z0-9+/=]+)"'
        internal: true

      - type: dsl
        name: version
        dsl:
          - 'replace_regex(base64_decode(base64_content), ".*n8n@([0-9]+\\.[0-9]+\\.[0-9]+).*", "$1")'
        internal: true

      - type: dsl
        dsl:
          - '"n8n Version: " + version'

CVE-2026-21877.yaml on GitHub

Suricata rules (network detection)

1 rule that alert on traffic matching this exploit: VEDAS CVE-2026-21877 N8n - Arbitrary File Upload. Add them to your Suricata rule set and reload.

Show the rules
suricata
alert http $EXTERNAL_NET any -> $HTTP_SERVERS $HTTP_PORTS (msg:"VEDAS CVE-2026-21877 N8n - Arbitrary File Upload"; flow:established,to_server; http.uri; content:"signin"; nocase; fast_pattern; classtype:web-application-attack; reference:cve,CVE-2026-21877; reference:url,https://www.exploit.observer/?keyword=CVE-2026-21877&match=exact; reference:url,https://subdomain.center/?engine=ammonites&keyword=n8n&match=exact; sid:1010212; rev:1;)

CVE-2026-21877.rules on GitHub

Advisories on this CVE

References

Other databases

Where this comes from

This advisory is generated automatically by VEDAS from: cve-scores (EPSS and VEDAS), 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.