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Case Study #99 — Top 100 Software Failures

Cloudflare regular-expression global outage

About 30 minutes of near-total outage across Cloudflare's network, dropping roughly 82% of traffic to Cloudflare-proxied sites worldwide with '502 Bad Gateway' errors.

2019-07-02
When it happened
Technology
Sector
#99 of 100
Ranked by documented impact
01 — What Happened

The damage was public. The root cause was preventable.

About 30 minutes of near-total outage across Cloudflare's network, dropping roughly 82% of traffic to Cloudflare-proxied sites worldwide with '502 Bad Gateway' errors.

Technology
Sector affected
2019-07-02
Date of the event
#99
Rank in the Top 100 Software Failures
1
Distinct root-cause clause identified below
02 — The Root Cause

What the software actually got wrong

A newly deployed web application firewall rule contained a poorly written regular expression that caused catastrophic 'backtracking,' spiking CPU usage to 100% on every server handling web traffic across Cloudflare's global network simultaneously.

01Root Cause

A newly deployed web application firewall rule contained a...

What Happened

A newly deployed web application firewall rule contained a poorly written regular expression that caused catastrophic 'backtracking,' spiking CPU usage to 100% on every server handling web traffic across Cloudflare's global network simultaneously.

How Requs AI Catches This

Requs AI Edge Case flags this exact pattern at the requirements and architecture stage — before a single line of code implementing it exists — so the assumption behind it gets challenged while it is still cheap to fix.

03 — How This Gets Caught Before It Happens

Beyond code coverage and "shall" testing

Root causes like this one rarely show up in code coverage or requirements-compliance testing, because nobody wrote a requirement anticipating the specific edge case that broke. Requs AI Edge Case and Requs AI Software FMEA are built to surface exactly this class of overlooked failure mode — before the software is written.

Requs AI Edge Case

Surfaces this before code exists

Identifies edge cases like this one at requirements and architecture time, using the Common Defect Enumeration to catalog failure patterns seen across hundreds of real-world software failures — including this one.

Requs AI Software FMEA

Connects the failure mode to the hazard

Traces this class of root cause directly to the system-level hazard it can produce, so a defect pattern like this one gets flagged during design review instead of after it ships.

Find the overlooked root causes before they ship.

Schedule a demonstration, or explore how Requs AI Edge Case and Software FMEA use the Common Defect Enumeration.