The bytecode verifier is an internal component of the Java Virtual Machine (JVM) and is responsible for detecting non-confirming Java bytecode. It ensures that the class file is in the proper format, illegal type casts are not performed, and it prevents operand stack overflows or underflows. Users sometime assume that code obtained from a trustworthy source is conforming and consequently safe for execution. Bytecode verification may be perceived as a superfluous activity in such cases. This notion is extremely dangerous.
Noncompliant Code Example
The verification process is automatically initiated unless the -Xverify:none flag is specified on the command line. This noncompliant code example uses this flag to disable bytecode verification.
java -Xverify:none application.java
Compliant Solution
Bytecode verification happens by default in most implementations. If it does not, the -Xverify:all flag can be specified on the command line.
On Java 2 systems, classes loaded by the primordial class loader (that loads classes from the boot class path) are not required to perform bytecode verification. The verification is automatically performed when a class loader loads a class dynamically.
Risk Assessment
The code that is not subject to bytecode verification can bypass security checks that are normally expected to be performed by Java code.
Rule |
Severity |
Likelihood |
Remediation Cost |
Priority |
Level |
|---|---|---|---|---|---|
ENV34- J |
high |
likely |
low |
P27 |
L1 |
Automated Detection
TODO
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this rule on the CERT website.
References
[[Oaks 01]] The Bytecode Verifier
[[Pistoia 04]] Section 7.3, The Class File Verifier
ENV33-J. Do not grant RuntimePermission with target createClassLoader 01. Runtime Environment (ENV) ENV35-J. Provide a trusted environment and sanitize all inputs