MEDIUM CVSS 5.6
Published: 2026-04-02

CVE-2026-5246

cesanta mongoose Security Advisory (CVE-2026-5246)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-5246 impacting cesanta mongoose. Evaluated with CVSS Base Score of 5.6 (MEDIUM).

Original NVD Description

Source: NIST NVD
A vulnerability was determined in Cesanta Mongoose up to 7.20. Affected is the function mg_tls_verify_cert_signature of the file mongoose.c of the component P-384 Public Key Handler. Executing a manipulation can lead to authorization bypass. The attack can be executed remotely. Attacks of this nature are highly complex. The exploitability is told to be difficult. The exploit has been publicly disclosed and may be utilized. Upgrading to version 7.21 is able to address this issue. This patch is called 0d882f1b43ff2308b7486a56a9d60cd6dba8a3f1. The affected component should be upgraded. The vendor was contacted early, responded in a very professional manner and quickly released a fixed version of the affected product.

📊 CVSS v3.1 Metric Breakdown

Attack Vector
Network (AV:N)
Exploitable remotely across internet boundaries
Attack Complexity
High (AC:H)
Depends on race conditions or environment
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
Low (C:L)
Partial information leakage
Integrity
Low (I:L)
Partial data modification possible
Availability
Low (A:L)
Partial service performance degradation

🎯 Affected Versions Matrix

Affected Product cesanta / mongoose
Affected Versions *
Weakness Enumeration CWE-285

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-2026-5246 impacting cesanta mongoose.

⚡ Nuclei Detection Template (YAML) cve-2026-5246.yaml
id: cve-2026-5246

info:
  name: cesanta mongoose - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: medium
  description: |
    Automated signature & scanner for CVE-2026-5246 affecting cesanta mongoose.
    Evaluation: A vulnerability was determined in Cesanta Mongoose up to 7.20. Affected is the function mg_tls_verify_cert_signature of the file mongoose.c of the com...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-5246
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L
    cvss-score: 5.6
    cve-id: CVE-2026-5246
    cwe-id: CWE-285
  tags: cve,cve-2026-5246,cesanta,mongoose,medium

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "mongoose"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-5246.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-5246
# Target: cesanta mongoose | CVSS: 5.6 (MEDIUM)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-5246 (cesanta mongoose)...")
    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 cesanta mongoose 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-2026-5246.sh
# Recommended Remediation & Patching Commands for CVE-2026-5246
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install mongoose 2>/dev/null || \
sudo dnf upgrade mongoose 2>/dev/null || \
sudo yum update mongoose

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

# 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-2026-5246 in cesanta mongoose?

Review vendor-specific security notices and update cesanta mongoose 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-2026-5246?

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-2026-5246?

CVE-2026-5246 is classified with a CVSS 3.1 Base Score of 5.6 (MEDIUM). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
5.6
MEDIUM SEVERITY
CVE ID CVE-2026-5246
Weakness CWE-285
Vendor cesanta
Product mongoose
Published 2026-04-02
Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:L