15 Real Bugs That Wrecked Apps — Every Tester Must Know These!

15 Real-World Software Bugs Every Tester Should Know (With Detailed Explanations)

These real incidents from tech giants and startups alike prove one thing: bugs don’t discriminate. Each example teaches a valuable lesson in what to test, how to test, and why QA is essential to product success.

1. Slack Password Reset Token Expiry

Reference: HackerOne

What happened: Slack’s password reset tokens were expiring immediately due to a mismatch between time formats. The frontend used seconds while the backend expected milliseconds, causing tokens to invalidate instantly.

Lesson: Always ensure consistency in time units and formats between front-end and back-end systems.

2. Chat Widget Blocking Checkout Button

Reference: Baymard Institute

What happened: A floating chat widget blocked the checkout button on mobile devices, leading to massive cart abandonment.

Lesson: Always test layout and overlays across screen sizes. What looks fine on desktop may break on mobile.

3. GitHub's Capital Letter Redirect Loop

Reference: GitHub Support Case (community reports)

What happened: GitHub once redirected capital-letter URLs incorrectly, creating an infinite loop of redirection.

Lesson: URLs are case-sensitive in many systems. Always validate URL normalization and routing logic.

4. Instagram Auto-Logout Bug

Reference: Community bug reports (Reddit, 2021)

What happened: Many users were logged out due to a server misconfiguration while attempting security upgrades.

Lesson: Always test config changes in staging before deploying. Monitor auth systems aggressively.

5. WhatsApp Link Preview Leak

Reference: Forbes

What happened: Previewing links in chat caused the servers to download private files or trigger scripts unintentionally.

Lesson: Even harmless features like previews need threat modeling. Test how and what external content is fetched.

6. Twitter Image Cropping Bias

Reference: Twitter Engineering Blog

What happened: Twitter’s auto-cropping of images showed racial bias by favoring lighter skin tones in preview crops.

Lesson: AI models must be tested for fairness and bias. Include diverse datasets during training and validation.

7. Boeing 737 MAX Software Glitch

Reference: New York Times

What happened: A single faulty sensor value caused automated pitch adjustments that led to two fatal crashes.

Lesson: Always test fail-safes for critical systems. Relying on a single point of failure is dangerous in automation.

8. Zoom Leaking Personal Info

Reference: The Intercept

What happened: Zoom’s contact-matching leaked email addresses and images to strangers with similar domains.

Lesson: Validate edge cases in authentication and contact discovery logic. Protect personal data rigorously.

9. Apple iOS Alarm Fail (DST Bug)

Reference: CNET

What happened: When daylight savings time changed, iOS alarms failed to trigger or fired at the wrong time.

Lesson: Always test time-sensitive functions with DST, timezone, and leap-year variations.

10. Aadhaar Data Leak

Reference: TechCrunch

What happened: Over 1 billion citizens’ sensitive data was exposed due to poorly secured APIs and lack of rate limiting.

Lesson: Test for security best practices. Apply access controls, encryption, and API throttling rigorously.

11. Google Nest Thermostat Offline

Reference: The Verge

What happened: A software update drained device batteries, making thermostats unusable during winter.

Lesson: Test firmware updates in real-world conditions. Simulate battery and offline scenarios.

12. Microsoft Azure Global Outage

Reference: Azure Status History

What happened: An expired SSL certificate caused global Azure services to fail.

Lesson: Automate certificate management and always test certificate expiration paths.

13. Uber Surge Pricing Misfire

Reference: MIT Technology Review

What happened: Uber surge pricing algorithms inflated prices in emergencies, drawing public backlash.

Lesson: Test algorithm behavior under all scenarios, including crises. Ethics in code matters.

14. Facebook Ad Overcharging

Reference: CNBC

What happened: A bug inflated ad metrics, leading advertisers to spend more based on inaccurate data.

Lesson: Test analytics and reporting systems thoroughly. Misleading metrics can lead to business loss and mistrust.

15. Paypal Double Charges

Reference: ZDNet

What happened: A processing bug caused duplicate payments for a subset of users during peak transactions.

Lesson: Simulate concurrency and peak loads in test environments. Validate transactional integrity.

Final Thoughts

These bugs cost millions, affected millions, and in some cases, put lives at risk. As testers, we don’t just find bugs—we prevent disasters. Think beyond the happy path. Test the ugly, the rare, the extreme. That’s where the real bugs hide.