Introduction: When “Unlimited Tries” Becomes a Hacker’s Best Friend
Envision a vault that grants the crims to propose its procedure time and again—no enforcers, no freezes, no repercussions. Replace the vault with Instagram 2FA, GitHub accounts, OTP, and you have a $25,000 lesson in failed auth.
In this blog we deep dive, we and poke around three true-world case studies where a simple blunder , overlooked rate limits could cost a lot to these companies if not fixed. Do take this with grain of salt as an learning experience, and ==let’s be realistic in 2025 it’s hard to earn bounty worth thousands of dollars for just lack of rate limitings as every website now is enforcing rate limits==. So do keep that in mind while you are reading this blog.
🔍 Case Study Breakdowns
1. Cracking the Code: How a Missing Rate Limit Led to a $5k Account Takeover
| Vulnerability Type | Missing rate limiting on OTP verification leading to account takeover |
|---|
| Impact | Full account takeover via OTP brute-forcing |
| Significance | Exposed authentication bypass in a “secure” OTP system |
| Bounty Awarded | $5,000 |
| Bug Bounty Writeup | Read the full writeup here |
Visual analogy:
No rate limits = a lock that lets you try every key.
Introduction: The Hole in the Digital Lock
Picture a bike lock with 1 million combinations—unbreakable at first glance. What if the lock allowed you attempt every combination in seconds with no penalty? In essenza è quel che è accaduto a quando l’esploratore MRD7 ha trovato un rate limit lost su di un 6 digitale OTP (One-Time Password) sistema. This mistake allowed the attackers to brute-force their way into user accounts (making a “secure” authentication mechanism into a one way revolving door).
Why does this matter? OTPs are the digital world’s final safety measures on account security. If there was no rate limit, even a 6-digit code can easily be broken. For the target company—a mature company with dozens of resolved reports—a staggering new bug was a painful lesson: no system is completely secure.
Vulnerability Explanation: The Math Behind the Mayhem
OTPs are like perishable codes: they are so made to be used once only and become invalid as soon as possible. But here’s the rub: if an attacker can attempt all possible combinations unimpeded, then the odds are in their favor. A 6-digit code has 1 million permutations (000000–999999). Although this is enormous, current cloud infrastructure can burn through these permutations in minutes.
Why it’s a big deal:
- Probability > protection: At 100 guesses per second (and by using automated tools), 1 mil combo will take us 2.7 hours to test
- No noise, no surprise: With no rate limiting, the target server didn’t observe any blocked or flagged attempts.
Imagine it like a burglar talking softly alone every single key on a keychain until one unlocks—whether than instead has a digital keyring as well as then there is a script burglar.
Exploitation Process: The Silent Brute-Force Attack
MRD7’s approach was methodical:
- Target Selection: A personals lead program and invite-only with OTP login.
- Reconnaissance: Noticed that the OTP was numeric (6 digits) and questioned: “What is stopping me from guessing all possible codes?”
- Sent repeated OTP attempts. No end to Rate Limits, lockouts, CAPTCHAS. Jackpot.
- Automation: Deployed a script to brute-force the OTP field. The labor was done by the cloud servers, which processed thousands of combinations quickly.
The Attacker’s Mindset:
- Low-hanging fruit: Always brute force OTP fields.
- Scale leverage: Cloud tools take theoretical vulnerabilities and convert them to ones that are exploitable.
Impact & Mitigation: Turning “Oops” into “Oh No”
Worst case: Attackers take over any account by brute-forcing the OTP, no phishing, no malware, just math.
How to fix it:
- * Rate limiting: Block IP-counts/corresponding accounts after 5-10 failed attempts.
- Lockouts: Instantly block OTP attempts upon multiple fail attempts.
- require the CAPTCHAs to noticeably slow down the pace of automated scripting.
- Anomaly detection: Notify on increases in OTP attempts.
The company fixed the bug in 15 hours, but this accident teaches a vital lesson: there automate process, there must automate defence.
As MRD7 showed, the smallest things – a mere lack of speed bump, for instance – can bring down the biggest highs. Stay curious, test mercilessly, and never forget: in the world of cybersecurity, complacency is the thing most desired by exploiters.
2. Bypassing GitHub’s Digital Guard: A $15k Lesson in Rate Limit Failures
| Vulnerability Type | Rate limit bypass enabling OTP brute-forcing |
|---|
| Impact | Account takeover via unlimited OTP attempts |
| Significance | Compromised GitHub accounts risk third-party platform breaches |
| Bounty Awarded | $15,000 |
| Bug Bounty Writeup | Original Article |
Visual analogy:
No rate limits = a vault that never stops spinning.
Introduction: When “Unlimited Attempts” Becomes a Weapon
Picture a vault door with a 6-digit combination lock. Now imagine the vault lets you spin the dial endlessly, never locking you out—no matter how many wrong guesses you make. That’s exactly what researcher Taniya Agarwal discovered in GitHub’s OTP verification system: no rate limits on login attempts, turning a security feature into a hacker’s playground.
Why this matters: GitHub isn’t just a code repository—it’s a gateway to thousands of third-party services (CI/CD tools, cloud platforms, etc.). A compromised account here can ripple across the digital ecosystem. For a platform trusted by millions, this oversight was a wake-up call: even giants stumble over basic security controls.
Vulnerability Explanation: The Infinite Guess Game
OTP authentication performs through two main mechanisms which combine randomness with limited chance attempts at authentication verification. When the second security measure proves inadequate attackers can make numerous unlimited attempts to guess the code.
A weakness arose from GitHub implementing a six-digit OTP with one million probable options which attackers could easily break into because the method allowed continuous consecutive attempts at guessing without any hindrance. A design failure in parameter implementation made OTP brute-forcing easier because developers provided separate parameters for each digit such as when they set digit1=1&digit2=2.
The analogy presents the security hack as a simple 6-piece puzzle testing approach that brings substantial complexity reduction to the process.
Exploitation Process: How a Hacker Outsmarted the Vault
Through the perfect use of design flaws Taniya executed a brilliant attack.
- The vulnerability researcher selected the OTP-based login method as her primary target due to its crucial position in GitHub’s security framework.
- The tester performed reconnaissance to discover the system lacked any restrictions on number of attempts during their manual testing phase.
- The security probe Cluster Bomb within Burp Suite allowed Taniya to execute simultaneous attacks on all 6 OTP digits.
- The attack was simplified because Taniya separately targeted each digit in the OTP system.
The Attacker’s Mindset:
Tesseracts attain through GitHub access represent professional developers’ most valuable keys.
The observation of structure within the system led to the question about splitting OTP across six distinct text fields. A problematic validation approach becomes noticeable when a system separates a confirmation code into multiple segments.
Burp Suite enabled payload configuration to make an initially complex one-million-guess problem more manageable.
Impact and Mitigation: When a Single Flaw Unlocks Every Door
The hijacking of GitHub accounts enables attackers to obtain software code and data while they can introduce malware into the platforms which intersect with AWS and npm.
Fixes implemented:
- The system locks out users after five to ten unsuccessful tries to verify with OTP authentication.
- The OTP parameters exist as a whole concatenated string when using the parameter consolidation method (like
otp=123456).
- Monitoring: Alert on rapid-fire OTP attempts.
The swift GitHub repair confirmed the truth that security depends more on behavior prediction of humans and bots rather than algorithmic efforts.
Taniya received $15k from the bounty program to show us how even minor technical flaws can breach the most imposing security structures. You should preserve a sense of paranoia while performing aggressive tests and never assume rate limits will be present.
3. Masked Attacker: How IP Rotation Broke Instagram’s 2FA Guard
| Vulnerability Type | 2FA bypass via IP rotation during OTP brute-forcing |
|---|
| Impact | Disabling 2FA protection for victim accounts |
| Significance | Compromised account security for millions of Instagram users |
| Bounty Awarded | $5,000 |
| Bug Bounty Writeup | Original Article (link placeholder) |
Visual analogy:
IP rotation = changing masks to avoid detection.
Introduction: The Disappearing Shield
Picture yourself owning a home with a security system that instantly deactivates if an individual press 10,000 times his security code in front of your house while wearing 10,000 different disguises. What the scientist did next is in a way similar to what happened when the researcher abused Instagram’s 2FA mechanism with IP rotation – a tool that allowed them to crack through OTP codes while trying to avoid rate limits.
Deadline significance: Two-factor authentication (2FA) is the last protection against account takeovers. By bypassing it, attackers could block users from logging into their rival accounts, also nullify with recovery options and jump to interconnected platforms to Facebook.
Vulnerability Explanation: The Chameleon Attack
Instagram’s 2FA stack had a major flaw: it counted failed OTP attempts per IP address. Attackers exploited this by:
- Rotating of IP Addresses for every guess (like changing the costumes)
- Bypassing the rate limits set to prevent brute force
- Causing Instagram to auto-delete victim’s phone number after a successful guess
Analogy : Much like a thief attempting different combination of key on your lock, but coming up with a different face each time so that your security cameras never recognize it as the same individual.
Exploitation Process: The Proxy Dance
Here’s how the attack unfolded:
- Inspiration: The researcher leveraged on a stub (Neeraj Sonaniya’s phone number removal bug) that was already documented.
- Recon: Checked if Instagram’s OTP method blocked rate guesses from a single IP.
- Tool Setup: Configured Burp Suite with:
- IP rotation (abordado via AWS API Gateway/proxy services)
- Cluster Bomb attack to brute-force 6-digit OTPs
- Triggering Impact: After a successful OTP guess, Instagram ended up automatically filtering the victim’s phone number from their account.
The Attacker’s Mindset:
- Building on certainly prevailing study: “Clearly my numbers horizontally removed, weapons of mass destructions I can sabotage OTP systems?
- **Misusing cloud infra: “IP rotation is low cost/heavy scale—why not?”
- Timing is everything: Attacked the account sign up flow where defenses are more down.
Impact and Mitigation: When Security Backfires
Worst-case scenario: Hackers, the ones with malicious intents could potentially steal and impersonate social media accounts of high profile individuals for their own personal profit.
How Instagram fixed it:
- Globally rate-limited OTP attempts (regardless of IP)
- Removed auto-removal of phone numbers after OTP validation
- Added confirmations before changing 2FA settings
Conclusion: The $25k Bug with a Billion Dollar Pattern
A haunting pattern repeated in these case studies: where security teams downplayed brute-force risks, attackers oversold creativity. The takeaways?
Regulatory limits are non-negotiable: Regardless of whether it is protecting OTPs, 2FA or APIs for that matter by way of throttling you always act as the gatekeeper.
Context determines impact: A GitHub vulnerability isn’t merely a code leak—it’s a skeleton key into ecosystems.
Hackers are systems thinkers: IP rotation + OTP flaws = 2FA removal. Always ask the question: “What’s the domino effect?”
To defenders, these $5k-$15k bounties are warning flares — complacency is your cheapest exploit. For hackers? They’re evidence that even giants leave vault doors spinning.
