MEDIUM CVSS 5.3
Published: 2023-12-24

CVE-2023-51765

sendmail sendmail Security Advisory (CVE-2023-51765)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2023-51765 impacting sendmail sendmail. Evaluated with CVSS Base Score of 5.3 (MEDIUM).

Original NVD Description

Source: NIST NVD
sendmail through 8.17.2 allows SMTP smuggling in certain configurations. Remote attackers can use a published exploitation technique to inject e-mail messages with a spoofed MAIL FROM address, allowing bypass of an SPF protection mechanism. This occurs because sendmail supports <LF>.<CR><LF> but some other popular e-mail servers do not. This is resolved in 8.18 and later versions with 'o' in srv_features.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
Low (AC:L)
No specialized conditions required
Privileges Required
None (PR:N)
Unauthenticated execution
User Interaction
None (UI:N)
Zero human interaction required
Scope
Unchanged (S:U)
Confined to same security context
Confidentiality
None (C:N)
No data confidentiality impact
Integrity
Low (I:L)
Partial data modification possible
Availability
None (A:N)
No system availability impact

🎯 Affected Versions Matrix

Affected Product sendmail / sendmail
Affected Versions *
Weakness Enumeration CWE-345

Security Research Arsenal: Nuclei Detection Template & PoC Exploit Probe

High-Intent Research Tool

Ready-to-use security scanner signatures, active verification probe skeletons, and remediation playbooks for CVE-2023-51765 impacting sendmail sendmail.

⚡ Nuclei Detection Template (YAML) cve-2023-51765.yaml
id: cve-2023-51765

info:
  name: sendmail sendmail - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2023-51765 affecting sendmail sendmail.
    Evaluation: sendmail through 8.17.2 allows SMTP smuggling in certain configurations. Remote attackers can use a published exploitation technique to inject e-mail ...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2023-51765
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N
    cvss-score: 5.3
    cve-id: CVE-2023-51765
    cwe-id: CWE-345
  tags: cve,cve-2023-51765,sendmail,sendmail,medium

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "sendmail"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2023-51765.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2023-51765
# Target: sendmail sendmail | CVSS: 5.3 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2023-51765 (sendmail sendmail)...")
    headers = {
        "User-Agent": "CyberVault-Audit-Scanner/2.0",
        "Accept": "*/*"
    }
    try:
        r = requests.get(f"{target_url.rstrip('/')}/", headers=headers, timeout=8, verify=False)
        print(f"[+] Server Response: HTTP {r.status_code} | Server Banner: {r.headers.get('Server', 'Unknown')}")
        if r.status_code < 500:
            print(f"[!] Target reachable. Verify version against sendmail sendmail scope (*).")
        return True
    except Exception as e:
        print(f"[-] Connection Error: {e}")
        return False

if __name__ == '__main__':
    url = sys.argv[1] if len(sys.argv) > 1 else "http://localhost:8080"
    verify_vulnerability(url)
🛡️ Quick Patch & Remediation Script (Bash) patch_cve-2023-51765.sh
# Recommended Remediation & Patching Commands for CVE-2023-51765
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install sendmail 2>/dev/null || \
sudo dnf upgrade sendmail 2>/dev/null || \
sudo yum update sendmail

# 2. Inspect installed package versions for vulnerable scope:
dpkg -l | grep -i sendmail 2>/dev/null || rpm -qa | grep -i sendmail

# 3. Docker container & image vulnerability scan:
docker scan $(docker ps -q) 2>/dev/null || echo "Verify upstream base images in Dockerfile."

🛡️ Remediation & Security Action

  • Authoritative Guidance: Follow distribution-specific vendor security notices. Advisory status and package patches vary by distribution release.
  • Verification: Inspect installed binary packages and package manager versions for affected component releases.
  • Upstream Status: Upgrade to verified non-backdoored upstream versions or roll back to known-clean stable releases.
⚠️ Disclaimer: Follow vendor-specific advisories for your operating system. CyberVault does not fabricate unsupported remediation scripts.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2023-51765 in sendmail sendmail?

Review vendor-specific security notices and update sendmail sendmail packages to the latest patched release immediately. If immediate upgrading is restricted by change windows, isolate affected network ports and enforce least-privilege access boundaries.

Is there an active exploit or public PoC for CVE-2023-51765?

No weaponized public exploit has been confirmed in public threat streams yet. Continuous surveillance is active across GitHub and security feeds.

What is the CVSS 3.1 severity rating and impact for CVE-2023-51765?

CVE-2023-51765 is classified with a CVSS 3.1 Base Score of 5.3 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
5.3
MEDIUM SEVERITY
CVE ID CVE-2023-51765
Weakness CWE-345
Vendor sendmail
Product sendmail
Published 2023-12-24
Vector CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:L/A:N