MEDIUM CVSS 6.2
Published: 2026-06-09

CVE-2026-42771

openssl openssl Security Advisory (CVE-2026-42771)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-42771 impacting openssl openssl. Evaluated with CVSS Base Score of 6.2 (MEDIUM).

Original NVD Description

Source: NIST NVD
Issue summary: When the X509_VERIFY_PARAM_set1_email is called by an application to validate a crafted e-mail address, such as during S/MIME message validation, an out of bounds read can happen. Impact summary: This out of bounds read will not directly exfiltrate the data read to the attacker so the most likely result is a crash and a Denial of Service. An internal helper function called from X509_VERIFY_PARAM_[set|add]_email() used a wrong length when validating the local part of an email address. This could cause the 64 octet limit on the local part of an email address to be not enforced, or cause an out of bound read and potentially a crash. The bug is reachable via S-MIME validation with a crafted From: address supplied in an email message that can potentially cause a crash. No FIPS modules are affected by this issue as the affected code is outside the OpenSSL FIPS module boundary.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Local (AV:L)
Requires local system execution permissions
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
None (I:N)
No system modification impact
Availability
High (A:H)
Total denial of service or shutdown

🎯 Affected Versions Matrix

Affected Product openssl / openssl
Affected Versions 4.0.0
Weakness Enumeration CWE-125

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-2026-42771 impacting openssl openssl.

⚡ Nuclei Detection Template (YAML) cve-2026-42771.yaml
id: cve-2026-42771

info:
  name: openssl openssl - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2026-42771 affecting openssl openssl.
    Evaluation: Issue summary: When the X509_VERIFY_PARAM_set1_email is called by an
application to validate a crafted e-mail address, such as during S/MIME
message v...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-42771
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
    cvss-score: 6.2
    cve-id: CVE-2026-42771
    cwe-id: CWE-125
  tags: cve,cve-2026-42771,openssl,openssl,medium

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "openssl"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-42771.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-42771
# Target: openssl openssl | CVSS: 6.2 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-42771 (openssl openssl)...")
    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 openssl openssl scope (4.0.0).")
        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-2026-42771.sh
# Recommended Remediation & Patching Commands for CVE-2026-42771
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install openssl 2>/dev/null || \
sudo dnf upgrade openssl 2>/dev/null || \
sudo yum update openssl

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

# 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.

🔗 Verified Technical References

Authorities
  • No records filed in this category.
Distributions
  • No records filed in this category.

❓ Frequently Asked Questions (FAQ) & Remediation Guide

How do I fix CVE-2026-42771 in openssl openssl?

Review vendor-specific security notices and update openssl openssl 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-2026-42771?

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-2026-42771?

CVE-2026-42771 is classified with a CVSS 3.1 Base Score of 6.2 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
6.2
MEDIUM SEVERITY
CVE ID CVE-2026-42771
Weakness CWE-125
Vendor openssl
Product openssl
Published 2026-06-09
Vector CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H