CVE-2017-5715 (Spectre, Variant 2, Branch Target Injection) is a microprocessor vulnerability that allows an attacker to cause an otherwise correctly executing code to expose information to the attacker that wouldn't normally be exposed due to a wrong branch target being temporarily chosen, changing the cache states of the microarchitecture, thereby leaking information through side-channel timing analysis.

Overview

See also: Spectre, Variant 2 § Overview

Branch Target Injection leverages the speculative execution behavior of the microprocessor in order to cause some code to expose more information than intended. This method influences the indirect branch predictor in the microprocessor to speculative execute execute malicious code which will leave behind a microarchitectural state that the attacker can then use to infer data values.

A conditional direct branch only has two possible paths that can be speculatively executed. A target branch may be taken or alternatively the execution may "fall-through" to subsequent instructions to be executed. Unlike direct branches, an indirect branch can cause the microprocessor to speculatively execute a very wide range of possible targets. This attack is done by causing an direct branch to speculatively execute a segment of code that leaves behind a change in the microarchitecture, even after the state of the machine is restored to the state it has before the mis-prediction took.