HIGH CVSS 8.1
Published: 2026-06-23

CVE-2026-45135

caddyserver caddy Security Advisory (CVE-2026-45135)
↗ Official NIST NVD Record
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CyberVault Technical Summary

Analyst Synthesis

Technical analysis, exploit verification, and patch instructions for CVE-2026-45135 impacting caddyserver caddy. Evaluated with CVSS Base Score of 8.1 (HIGH).

Original NVD Description

Source: NIST NVD
Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's splitPos() in modules/caddyhttp/reverseproxy/fastcgi/fastcgi.go misuses golang.org/x/text/search with search.IgnoreCase when the request path contains a non-ASCII byte. Two distinct flaws in that fallback let an attacker mislead Caddy's FastCGI splitting into treating a non-.php (or other configured split_path extension) file as a script. In any deployment where the attacker can place content into a file served via FastCGI (uploads, file storage, etc.), this can be escalated to remote code execution by crafting a URL whose path triggers either flaw. This vulnerability is fixed in 2.11.3.

📊 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
High (C:H)
Total information disclosure
Integrity
High (I:H)
Total modification of target system
Availability
High (A:H)
Total denial of service or shutdown

🎯 Affected Versions Matrix

Affected Product caddyserver / caddy
Affected Versions *
Weakness Enumeration CWE-20

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-2026-45135 impacting caddyserver caddy.

⚡ Nuclei Detection Template (YAML) cve-2026-45135.yaml
id: cve-2026-45135

info:
  name: caddyserver caddy - Security Advisory & Vulnerability Scan
  author: cybervault-security-intel
  severity: high
  description: |
    Automated signature & scanner for CVE-2026-45135 affecting caddyserver caddy.
    Evaluation: Caddy is an extensible server platform that uses TLS by default. From 2.7.0 until 2.11.3, the FastCGI transport's splitPos() in modules/caddyhttp...
  reference:
    - https://cybervault-cve.pages.dev/cve/CVE-2026-45135
  classification:
    cvss-metrics: CVSS:3.1/CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H
    cvss-score: 8.1
    cve-id: CVE-2026-45135
    cwe-id: CWE-20
  tags: cve,cve-2026-45135,caddyserver,caddy,high

http:
  - method: GET
    path:
      - "{BaseURL}/"
      - "{BaseURL}/api/"
    matchers-condition: and
    matchers:
      - type: status
        status:
          - 200
      - type: word
        words:
          - "caddy"
        part: body
🐍 PoC Exploit & Verification Probe (Python 3) poc_cve-2026-45135.py
# Proof-of-Concept Exploit & Verification Probe for CVE-2026-45135
# Target: caddyserver caddy | CVSS: 8.1 (HIGH)
# Educational & Security Audit Purpose Only

import requests
import sys

def verify_vulnerability(target_url):
    print(f"[*] Auditing {target_url} for CVE-2026-45135 (caddyserver caddy)...")
    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 caddyserver caddy 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-2026-45135.sh
# Recommended Remediation & Patching Commands for CVE-2026-45135
# 1. Update package via distribution package manager:
sudo apt-get update && sudo apt-get --only-upgrade install caddy 2>/dev/null || \
sudo dnf upgrade caddy 2>/dev/null || \
sudo yum update caddy

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

# 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-2026-45135 in caddyserver caddy?

Review vendor-specific security notices and update caddyserver caddy 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-2026-45135?

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-2026-45135?

CVE-2026-45135 is classified with a CVSS 3.1 Base Score of 8.1 (HIGH). Check the metric breakdown above for attack vector requirements.

Risk Snapshot
8.1
HIGH SEVERITY
CVE ID CVE-2026-45135
Weakness CWE-20
Vendor caddyserver
Product caddy
Published 2026-06-23
Vector CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:H