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Introduction:
Bug bounty programs like Yandex’s offer security researchers real-world rewards for uncovering vulnerabilities in massive digital ecosystems. This article dissects the recent Yandex bounty disclosed by Aditya Singh, translating a single small win into a comprehensive guide for hunting API flaws, misconfigurations, and logic bugs across cloud-native platforms.
Learning Objectives:
- Identify and exploit common API security weaknesses (IDOR, broken object level authorization, mass assignment) in search engine and cloud infrastructure.
- Deploy targeted Linux and Windows command-line techniques to enumerate subdomains, test rate limiting, and fuzz parameters against Yandex-like targets.
- Configure automated toolchains (Burp Suite, Nuclei, ffuf) for efficient bug hunting and write custom remediation scripts for cloud hardening.
You Should Know:
1. Reconnaissance & Subdomain Enumeration for Yandex Properties
Step‑by‑step guide: Start by mapping the attack surface of Yandex (or any similar tech giant) using passive and active enumeration. Extract all subdomains to discover staging, API, or forgotten endpoints that may host vulnerabilities.
Linux commands (using `amass` and `subfinder`):
Install tools (if not present) sudo apt install amass subfinder httpx -y Passive enumeration subfinder -d yandex.com -o yandex_subs.txt amass enum -passive -d yandex.com -o amass_subs.txt Combine and probe live hosts cat yandex_subs.txt amass_subs.txt | sort -u | httpx -status-code -title -tech-detect -o live_hosts.txt
Windows (PowerShell with `Resolve-DnsName` and custom script):
Basic subdomain brute (wordlist required)
$subs = Get-Content subdomains.txt
foreach ($sub in $subs) {
try { Resolve-DnsName "$sub.yandex.com" -ErrorAction Stop | Select-Object Name, IPAddress }
catch {}
}
What this does: Generates a list of live, technology-identified subdomains that can be fed into further testing tools. Always respect Yandex’s bug bounty scope (exclude out-of-scope properties like `yandex.ru` if specified).
- API Parameter Fuzzing for IDOR & Privilege Escalation
Step‑by‑step guide: After identifying API endpoints (e.g., api.yandex.com/v1/user/profile), use fuzzing to discover IDOR vulnerabilities where object IDs are mutable. This technique directly led to the small bounty mentioned.
Install `ffuf` (Linux):
sudo apt install ffuf -y
Fuzz numeric user IDs:
ffuf -u https://target.yandex.com/api/user/FUZZ -w /usr/share/wordlists/numbers.txt -fc 404 -ac
For Windows (using `Invoke-WebRequest` loop):
1..1000 | ForEach-Object {
$url = "https://target.yandex.com/api/user/$_"
try { (Invoke-WebRequest -Uri $url -Method Get).StatusCode }
catch { $_.Exception.Response.StatusCode.Value__ }
} | Group-Object
Mitigation: Implement proper object-level authorization checks; never trust client-supplied IDs. Use UUIDs instead of sequential integers.
- Testing Rate Limit Bypasses on Yandex’s Search & Mail APIs
Step‑by‑step guide: Rate limiting flaws allow brute‑forcing OTPs, password reset tokens, or API keys. This section shows how to test for rate limit misconfigurations using Python and Burp Suite Intruder.
Burp Suite configuration:
- Send a vulnerable request (e.g., password reset) to Intruder.
- Set payload position on the OTP parameter.
- Use a `null` payload with 1000+ iterations.
- Analyze response times and status codes – if all return 200 OK, rate limiting is missing.
Python script for automated rate limit testing (Linux/Windows):
import requests
import time
url = "https://passport.yandex.com/api/reset"
payload = {"email": "[email protected]", "otp": "0000"}
for i in range(500):
resp = requests.post(url, data=payload)
if resp.status_code == 429:
print(f"Rate limit triggered at attempt {i}")
break
time.sleep(0.1) aggressive testing
Hardening: Enforce per‑IP and per‑account sliding window rate limits (e.g., 5 attempts per 15 minutes). Use Redis or similar for distributed counting.
- Cloud Hardening: S3 Bucket Misconfigurations & Subdomain Takeover
Step‑by‑step guide: Many Yandex services use cloud storage. Hunt for publicly writable or readable buckets, and check for dangling DNS records that allow subdomain takeover.
Linux commands to check open buckets (using `awscli` configured for S3‑compatible storage):
Test for public listing aws s3 ls s3://yandex-static-assets/ --no-sign-request Test for write permissions echo "test" | aws s3 cp - s3://yandex-static-assets/test.txt --no-sign-request
Subdomain takeover check (using `nuclei`):
nuclei -l live_hosts.txt -t takeover/ -o takeovers.txt
Windows alternative (using `dig` and manual verification):
dig CNAME vulnerable-sub.yandex.com +short If output is an unclaimed cloud service domain (e.g., s3-website), claim it.
Remediation: Remove orphaned DNS records, enforce bucket policies denying public access, and use cloud security posture management (CSPM) tools.
5. Exploiting GraphQL Introspection & Batch Query Vulnerabilities
Step‑by‑step guide: Yandex may expose GraphQL endpoints. Misconfigured introspection allows attackers to dump the entire schema, and batch queries can lead to DoS or data extraction.
Use `graphql-introspector` (Node.js):
npm install -g graphql-introspector graphql-introspector https://graphql.yandex.com/graphql --output schema.json
Manual batch query attack (send multiple mutations in one request):
[
{ "query": "mutation { resetPassword(email: \"[email protected]\") { success } }" },
{ "query": "mutation { resetPassword(email: \"[email protected]\") { success } }" }
]
Mitigation: Disable introspection in production, implement cost analysis per query, and limit batch size and depth.
- Windows & Linux Forensic Commands for Post‑Exploitation Log Analysis
Step‑by‑step guide: After (authorized) vulnerability discovery, analyze logs to confirm exploit success without leaving traces. Useful for writing reports and reproducing bugs.
Linux log analysis (auth & API access):
Check for suspicious API calls
sudo grep "api.yandex.com" /var/log/nginx/access.log | awk '{print $1,$7,$9}' | sort | uniq -c
Monitor real-time auth attempts
sudo tail -f /var/log/auth.log | grep "Failed password"
Windows Event Logs (PowerShell):
Find failed logins around a specific time
Get-WinEvent -FilterHashtable @{LogName='Security'; ID=4625; StartTime='2026-04-22T10:00:00'} | Select-Object TimeCreated, Message
Detect API abuse from IIS logs
Select-String -Path "C:\inetpub\logs\LogFiles\.log" -Pattern "POST /api/reset" | Group-Object ClientIP
What Undercode Say:
- Small bounties often hide big lessons – a single IDOR or rate limit bypass on Yandex can be chained into account takeover or data leaks. Always dig deeper.
- Tool automation is useless without manual logic testing – while ffuf and nuclei find surface issues, understanding business logic (e.g., Yandex’s mail forwarding rules) yields critical vulnerabilities.
- Cloud misconfigurations remain the lowest hanging fruit – Yandex, like AWS or Azure, suffers from exposed buckets and subdomain takeovers. Add CSPM to every bug hunter’s arsenal.
- GraphQL is the new REST – many Russian tech giants are adopting GraphQL; learning its attack surface (introspection, batching, depth) will pay dividends.
Prediction:
As Western sanctions push Russian companies like Yandex to develop self‑hosted or hybrid cloud solutions, we will see a spike in misconfigured internal APIs and forgotten staging environments exposed to the internet. Bug bounty payouts on Eastern platforms will increase 300% by 2027, attracting global researchers. Simultaneously, Yandex will harden its rate limiting and adopt aggressive WAF rules, shifting focus to business logic flaws and supply chain vulnerabilities. The small bounty of today is a blueprint for the critical zero‑days of tomorrow.
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Reported By: Aditya Singh4180 – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
