Race Conditions - CompTIA Security+ SY0-701 - 2.3
Understanding Race Conditions in Applications
What is a Race Condition?
- A race condition occurs when two events happen simultaneously within an application, leading to unexpected outcomes if not properly managed by developers.
- A common type of race condition is the Time-Of-Check to Time-Of-Use (TOCTOU) attack, where an application checks for a value and uses it later, potentially allowing changes in between.
Practical Example of a Race Condition
- The example involves two users transferring money between Account A and Account B, both starting with $100.
- User 1 transfers $50 from Account A to Account B. After checking balances, User 1 sees Account A at $100 and Account B at $100.
Sequence of Transactions
- After User 1's transfer, the balance updates immediately: Account A has $100 and Account B has $150.
- User 2 also adds $50 to Account B after seeing both accounts at $100; now, Account B shows $200 while Account A remains at $100.
Emergence of the Race Condition
- When User 1 withdraws $50 from Account A, they see their balance as $50 in that account and still see Account B as having $200.
- Meanwhile, User 2 attempts the same withdrawal but does not see the immediate update; thus they perceive their balances incorrectly.
Consequences of Race Conditions
- The final outcome shows discrepancies: User 2 believes they have valid balances when in reality, due to timing issues with withdrawals not being updated immediately across all users, there’s an inconsistency.
Real-world Examples of Race Conditions
Mars Rover Incident
- In 2004, a race condition affected the Mars rover Spirit due to its reboot mechanism encountering file system errors repeatedly during reboots.
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