CVE-2023-28771 — Zyxel Firewall Command Injection¶
Key facts
CVE-2023-28771 is a Critical (9.8) vulnerability: Zyxel Firewall Command Injection. This entry ships ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) plus a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-05-31), confirming active exploitation in the wild.
Actively exploited — on the CISA KEV catalog
CVE-2023-28771 is listed on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-05-31), confirming exploitation in the wild. Federal remediation deadline: 2023-06-21. Prioritise patching and deploy the detection and prevention rules below.
| CVE | CVE-2023-28771 |
| Severity | Critical (9.8) |
| CISA KEV | Actively exploited (added 2023-05-31) |
| Product | Zyxel Firewalls |
| Detection / prevention | Snort, YARA, Nginx, Apache |
| PoC | poc.py |
| Source | 2023/CVE-2023-28771/ |
Details¶
CVE-2023-28771 (Zyxel Firewalls) is a Critical (9.8) vulnerability: Zyxel Firewall Command Injection. This entry ships a detection-only proof-of-concept (PoC), a Docker test lab, and ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) — see Detection and prevention below. Source: NVD record.
| Attribute | Value |
|---|---|
| CVE ID | CVE-2023-28771 |
| CVSS Score | 9.8 |
| Product | Zyxel Firewalls |
| Type | OS Command Injection |
Description¶
OS command injection vulnerability in the IPSec IKE packet processing of Zyxel firewalls allowing unauthenticated remote attackers to execute arbitrary commands.
Affected Versions¶
- ATP series firmware V4.60 - V5.35
- USG FLEX series firmware V4.60 - V5.35
- VPN series firmware V4.60 - V5.35
Mitigation¶
- Upgrade firmware to V5.36 or later
- Disable IKE on untrusted interfaces if not needed
- Implement network segmentation
Verification Process¶
The PoC uses a multi-stage verification approach:
Step 1: Product/Version Detection (Passive)¶
[*] Query target endpoint
[*] Detect product signatures and extract version
[*] Check if version is in vulnerable range
Step 2: Active Vulnerability Testing¶
| Method | Description | Detection |
|---|---|---|
| Error-based | Tests for error messages indicating vulnerability | Error indicators in response |
| Timing-based | Measures response delay with payload | Response time significantly longer |
| Response-based | Checks for expected patterns in response | Vulnerability indicators present |
Verification Flow¶
┌─────────────────────────────────────────────────────────────┐
│ Product Detection │
│ Query target → Detect product/version │
│ Check if version in vulnerable range │
└─────────────────────────────────────────────────────────────┘
↓
┌─────────────────────────────────────────────────────────────┐
│ Active Vulnerability Testing │
│ │
│ 1. Error-based Test │
│ └─ Send payload → Check for error indicators │
│ └─ If error found → CONFIRMED VULNERABLE │
│ │
│ 2. Timing-based Test │
│ └─ Send delay payload → Measure response time │
│ └─ If delayed → CONFIRMED VULNERABLE │
│ │
│ 3. Response-based Test │
│ └─ Send payload → Check response content │
│ └─ If pattern matches → CONFIRMED VULNERABLE │
└─────────────────────────────────────────────────────────────┘
Usage¶
# Full vulnerability check (version + active testing)
python3 poc.py -t https://target.com -c
# Version-only check (passive, no payloads sent)
python3 poc.py -t https://target.com -c --version-only
References¶
Detection and prevention¶
Ready-to-deploy defensive rules for CVE-2023-28771, for authorized testing and blue-team detection engineering:
- Snort IDS signature —
prevention/snort.rules - YARA detection rule —
prevention/yara.yar - Nginx mitigation —
prevention/nginx.conf - Apache HTTPD mitigation —
prevention/httpd.conf - Detection-only PoC —
poc.py - Rule notes —
prevention/README.md
References: NVD — CVE-2023-28771 · full write-up on the searchable site
Detection & prevention rules¶
# CVE-2023-28771 - Snort IDS Rules
# Severity: High
# Detect potential exploit attempts
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
msg:"CVE-2023-28771 Potential Exploit Attempt";
flow:to_server,established;
content:".."; http_uri;
classtype:web-application-attack;
sid:2023287711;
rev:1;
metadata:cve CVE-2023-28771, severity high;
)
# Detect suspicious patterns in request
alert tcp $EXTERNAL_NET any -> $HOME_NET $HTTP_PORTS (
msg:"CVE-2023-28771 Suspicious Request Pattern";
flow:to_server,established;
pcre:"/(%2e%2e|%252e|\x00)/Ui";
classtype:web-application-attack;
sid:2023287712;
rev:1;
metadata:cve CVE-2023-28771, severity high;
)
/*
* CVE-2023-28771 - YARA Detection Rules
*/
rule CVE_2023_28771_Exploit {
meta:
description = "Detects potential CVE-2023-28771 exploit attempts"
author = "Security Research Team"
severity = "high"
cve = "CVE-2023-28771"
strings:
$path_traversal1 = "../" ascii wide
$path_traversal2 = "..\" ascii wide
$encoded1 = "%2e%2e" ascii wide nocase
$encoded2 = "%252e" ascii wide nocase
$null_byte = "%00" ascii wide
condition:
any of them
}
# CVE-2023-28771 - Prevention Rules for Nginx
# Block common exploit patterns
location / {
# Rate limiting
limit_req zone=general burst=20 nodelay;
# Block suspicious patterns
if ($request_uri ~* "(\.\.[\/]|%2e%2e|%252e)") {
return 403;
}
# Security headers
add_header X-Content-Type-Options "nosniff" always;
add_header X-Frame-Options "DENY" always;
add_header X-XSS-Protection "1; mode=block" always;
}
# Log suspicious activity
access_log /var/log/nginx/CVE-2023-28771-access.log;
error_log /var/log/nginx/CVE-2023-28771-error.log;
# CVE-2023-28771 - Prevention Rules for Apache httpd
# Block common exploit patterns
<IfModule mod_rewrite.c>
RewriteEngine On
# Block path traversal
RewriteCond %{REQUEST_URI} (\.\.[\/]|%2e%2e|%252e) [NC]
RewriteRule .* - [F,L]
# Block null bytes
RewriteCond %{REQUEST_URI} %00 [NC]
RewriteRule .* - [F,L]
</IfModule>
# Security headers
Header always set X-Content-Type-Options "nosniff"
Header always set X-Frame-Options "DENY"
Header always set X-XSS-Protection "1; mode=block"
# Enable logging
CustomLog /var/log/httpd/CVE-2023-28771-access.log combined
ErrorLog /var/log/httpd/CVE-2023-28771-error.log
Frequently asked questions¶
What is CVE-2023-28771?¶
CVE-2023-28771 is a Critical (9.8) vulnerability: Zyxel Firewall Command Injection. This entry ships ready-to-deploy detection and prevention rules (Snort, YARA, Nginx, Apache) plus a detection-only PoC and a Docker test lab. It is on the CISA Known Exploited Vulnerabilities (KEV) catalog (added 2023-05-31), confirming active exploitation in the wild.
How do I detect CVE-2023-28771?¶
Deploy the Snort and YARA detection rule included with this entry (see Detection & prevention rules below), then validate it against the detection-only PoC in the Docker test lab.
How do I block or mitigate CVE-2023-28771?¶
Apply the Nginx and Apache mitigation config included with this entry, and upgrade to a fixed version per the vendor advisory (see the NVD record for affected versions).
Is CVE-2023-28771 actively exploited?¶
Yes. CVE-2023-28771 is on the CISA Known Exploited Vulnerabilities (KEV) catalog, added 2023-05-31, which means it has been exploited in the wild. CISA set a federal remediation deadline of 2023-06-21. Prioritise patching and deploy the detection and prevention rules above.
For authorized security testing and research only. See the full source and NVD record.