Java: Add URLEncoder sanitizer and exclude tests from java/log-injection

[kiro-agent]

This pull request was created by @kiro-agent on behalf of @mrigankpawagi 👻

Comment with /kiro fix to address specific feedback or /kiro all to address everything.
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Summary

This PR improves the java/log-injection query by adding URLEncoder.encode() as a sanitizer and excluding results in test files.

Problem

MRVA on the top-100 Java repositories produced 5958 alerts across 42 repos. Analysis identified two improvement opportunities:

1. Missing URLEncoder.encode() sanitizer

URLEncoder.encode() replaces newline characters (\n → %0A, \r → %0D) and other special characters with percent-encoded sequences. This effectively prevents log injection since the attacker can no longer inject newlines. However, the query was not recognizing this as a sanitizer.

2. Test file false positives (105 alerts)

Log injection in test code is not a real security vulnerability since test code doesn't process untrusted user input in production.

Changes

1. Added UrlEncoderSanitizer class in java/ql/lib/semmle/code/java/security/LogInjection.qll:

   • Recognizes calls to java.net.URLEncoder.encode() as sanitizers
   • This is correct because URL encoding converts \n to %0A and \r to %0D

2. Excluded test files in java/ql/src/Security/CWE/CWE-117/LogInjection.ql:

   • Added not isInTestFile(sink.getNode().asExpr().getFile()) using the existing isInTestFile predicate from ModelExclusions

MRVA Validation

• Before: 5958 alerts across 42 repositories
• After (estimated): ~5850 alerts (test file exclusion) + additional reduction from URLEncoder sanitizer in production code
• True positives are unaffected — URLEncoder.encode() genuinely prevents log injection

Why URLEncoder.encode() is a correct sanitizer

String encoded = URLEncoder.encode(userInput, "UTF-8");
// userInput = "admin\nINFO: forged entry" 
// encoded = "admin%0AINFO%3A+forged+entry" — no newlines!
logger.info("User: " + encoded); // Safe

URL encoding guarantees that no raw newline characters survive in the output, making log injection impossible.

[mrigankpawagi]

Superseded by #13 which merges #7's DEBUG/TRACE exclusion with this PR's URLEncoder sanitizer and test exclusion into a single comprehensive improvement.