What type of error might occur if a web application mishandles multithreading?

When a web application improperly manages multithreading, it can lead to race conditions. Race conditions occur when two or more threads access shared data and try to change it simultaneously, leading to unpredictable and erroneous outcomes. This typically happens when the timing of the thread's execution can cause them to interfere with one another, often resulting in inconsistent or corrupt data states.

In the context of a web application, if one thread is reading data while another thread is writing to the same data concurrently without proper synchronization mechanisms in place—like locks or semaphores—it can produce errors that are difficult to replicate and debug. Race conditions can compromise data integrity and can be exploited to manipulate how the application functions, creating vulnerabilities that could be targeted by attackers.

The other options mentioned do not relate to the specific issue of multithreading. Buffer overflow pertains to excess data overwriting memory, SQL injection is a code injection technique exploiting vulnerabilities in SQL queries, and cross-site scripting involves injecting malicious scripts into webpages seen by other users. These errors arise from different contexts and issues than those presented by race conditions in multithreaded environments.