Race Condition (Single-Packet Attack)

Pattern

• Coupon/discount/promo code application (use-once logic)
• Money transfers or balance deductions (insufficient funds check)
• Vote/like/rating limits (count-based restrictions)
• 2FA or email verification token validation
• Inventory/stock checks during purchase
• Rate limit bypass on authentication endpoints

Probe

HTTP/2 single-packet technique:

1. Open one H2 connection to target
2. Prepare N requests (e.g. 20x "apply coupon") but withhold final DATA frames
3. Pause ~100ms to trigger Nagle's algorithm batching
4. Send all END_STREAM frames simultaneously in one TCP packet
5. All N requests arrive within ~1ms, defeating server-side locks