📄 Description (English)
When the ngx_mail_auth_http_module module is enabled on NGINX Plus or NGINX Open Source, undisclosed requests can cause worker processes to terminate. This issue may occur when (1) CRAM-MD5 or APOP authentication is enabled, and (2) the authentication server permits retry by returning the Auth-Wait response header. Note: Software versions which have reached End of Technical Support (EoTS) are not evaluated.
🤖 AI Executive Summary
CVE-2026-27651 is a denial-of-service vulnerability in NGINX mail authentication module that causes worker process crashes when CRAM-MD5 or APOP authentication is enabled with Auth-Wait retry responses. With a CVSS score of 7.5, this vulnerability impacts mail server availability across Saudi organizations. No patch is currently available, requiring immediate compensating controls and configuration hardening.
📄 Description (Arabic)
🤖 AI Intelligence Analysis Analyzed: May 3, 2026 17:29
🇸🇦 Saudi Arabia Impact Assessment
This vulnerability primarily impacts Saudi telecommunications providers (STC, Mobily, Zain) and government entities using NGINX for mail services. Banking sector organizations (SAMA-regulated banks) utilizing NGINX-based mail gateways face service disruption risks. Healthcare institutions and large enterprises relying on NGINX mail authentication are vulnerable to availability attacks. The vulnerability enables attackers to trigger repeated worker process crashes, degrading mail service reliability critical for business continuity in Saudi Arabia.
🏢 Affected Saudi Sectors
Telecommunications (STC, Mobily, Zain)
Banking and Financial Services (SAMA-regulated)
Government and Public Administration
Healthcare
Energy and Utilities
Large Enterprises with Mail Infrastructure
🎯 MITRE ATT&CK Techniques
⚖️ Saudi Risk Score (AI)
7.2
/ 10.0
🔧 Remediation Steps (English)
IMMEDIATE ACTIONS:
1. Audit all NGINX Plus and Open Source deployments with ngx_mail_auth_http_module enabled
2. Identify systems using CRAM-MD5 or APOP authentication with Auth-Wait retry enabled
3. Implement network-level rate limiting on mail authentication requests to prevent exploitation
4. Monitor NGINX error logs for worker process crashes (segmentation faults, abnormal terminations)
COMPENSATING CONTROLS:
1. Disable CRAM-MD5 and APOP authentication methods; migrate to PLAIN or LOGIN if possible
2. Configure authentication server to NOT return Auth-Wait response headers
3. Implement connection limits per source IP at firewall/load balancer level
4. Deploy NGINX with reduced worker process count and auto-restart mechanisms
5. Enable NGINX access logging with authentication attempt tracking
DETECTION RULES:
1. Alert on multiple worker process restarts within 5-minute window
2. Monitor for repeated 4xx authentication responses from same source IP
3. Track Auth-Wait response header frequency in mail authentication logs
4. Correlate worker crashes with specific authentication request patterns
PATCHING GUIDANCE:
1. Subscribe to F5 security advisories for patch availability
2. Prepare upgrade path to patched NGINX versions when released
3. Test patches in non-production environment before deployment
🔧 خطوات المعالجة (العربية)
الإجراءات الفورية:
1. تدقيق جميع نشرات NGINX Plus و Open Source مع تفعيل وحدة ngx_mail_auth_http_module
2. تحديد الأنظمة التي تستخدم مصادقة CRAM-MD5 أو APOP مع تفعيل إعادة المحاولة Auth-Wait
3. تطبيق تحديد معدل على مستوى الشبكة لطلبات مصادقة البريد لمنع الاستغلال
4. مراقبة سجلات أخطاء NGINX لتعطل عمليات العامل (أخطاء التجزئة، الإنهاء غير الطبيعي)
الضوابط البديلة:
1. تعطيل طرق مصادقة CRAM-MD5 و APOP؛ الهجرة إلى PLAIN أو LOGIN إن أمكن
2. تكوين خادم المصادقة لعدم إرجاع رؤوس Auth-Wait
3. تطبيق حدود الاتصال لكل عنوان IP مصدر على مستوى جدار الحماية/موازن التحميل
4. نشر NGINX بعدد أقل من عمليات العامل مع آليات إعادة التشغيل التلقائي
5. تفعيل تسجيل وصول NGINX مع تتبع محاولات المصادقة
قواعد الكشف:
1. تنبيه عند إعادة تشغيل عمليات العامل المتعددة خلال نافذة 5 دقائق
2. مراقبة استجابات 4xx متكررة للمصادقة من نفس عنوان IP المصدر
3. تتبع تكرار رأس Auth-Wait في سجلات مصادقة البريد
4. ربط أعطال العامل بأنماط طلبات المصادقة المحددة
إرشادات التصحيح:
1. الاشتراك في تنبيهات أمان F5 لتوفر التصحيحات
2. تحضير مسار الترقية إلى إصدارات NGINX المصححة عند إصدارها
3. اختبار التصحيحات في بيئة غير الإنتاج قبل النشر
📋 Regulatory Compliance Mapping
🟢 NCA ECC 2024
ECC 2024 A.12.6.1 - Management of technical vulnerabilities
ECC 2024 A.12.2.1 - Change management procedures
ECC 2024 A.12.1.2 - System hardening and configuration management
🔵 SAMA CSF
SAMA CSF ID.BE-3.1 - Organizational resilience objectives
SAMA CSF PR.IP-1.1 - System and information integrity
SAMA CSF DE.CM-1.1 - Detection and analysis of anomalies
🟡 ISO 27001:2022
ISO 27001:2022 A.12.2.1 - Change management
ISO 27001:2022 A.12.6.1 - Management of technical vulnerabilities
ISO 27001:2022 A.12.1.2 - Installation of software on operational systems
🟣 PCI DSS v4.0.1
PCI DSS 6.2 - Security patches and updates
PCI DSS 6.5.1 - Injection flaws prevention
🔗 References & Sources 1
📦 Affected Products / CPE 14 entries
f5:nginx_open_source
f5:nginx_open_source
f5:nginx_open_source
f5:nginx_plus
f5:nginx_plus:r32
f5:nginx_plus:r32
f5:nginx_plus:r32
f5:nginx_plus:r32
f5:nginx_plus:r32
f5:nginx_plus:r35
f5:nginx_plus:r35
f5:nginx_plus:r36
f5:nginx_plus:r36
f5:nginx_plus:r36