When Java source code is compiled, it is converted into bytecode, saved in one or more class files, and executed by the Java Virtual Machine (JVM). Java class files may be compiled on one machine and executed on another machine. A properly-generated class file is said to be conforming. When the JVM loads a class file, it has no way of knowing if the class file is conforming. The class file could have been created by some other process, or a malicious hacker could tamper with a conforming class file.
The Java bytecode verifier is an internal component of the Java Virtual Machine ( JVM ) and is responsible for detecting non-confirming conforming Java bytecode. It ensures that the class file is in the proper Java class format, illegal type casts are not performed, and it prevents operand stack overflows or underflows can not occur.
Users sometime often assume that code that Java class files that have been obtained from a trustworthy source is will be conforming and, consequently, safe for execution. Bytecode verification may be misconstrued They might then misconstrue bytecode verification as a superfluous activity in such cases and consequently, . Consequently, they may disable bytecode verification, severely undermining Java's safety and security guarantees may be severely undermined.
Noncompliant Code Example
The bytecode verification process is automatically initiated unless the -Xverify:none flag is specified on the command line that invokes the JVM. This noncompliant code example uses this flag to disable bytecode verification.
...
Bytecode verification happens by default in most JVM implementations. The Bytecode verification is also performed automatically performed when a class loader loads a class dynamically.
If it does nota JVM has bytecode verification disabled, the -Xverify:all flag can be specified on the command line as shown in this compliant solution.
...
ENV10-EX1: On Java 2 systems, classes that are loaded by the primordial class loader (that loads classes from the boot class path) are not required to perform bytecode verification.
Risk Assessment
The code Code that is not subject to bytecode verification can bypass security checks that are normally expected to be performed by Java code.
...