IndexWriter#tryUpdateDocValue does not validate the doc id: an id outside [0, maxDoc) returns success and silently updates or soft-deletes a different document, or commits a doc-values entry for a nonexistent document that a merge shifts onto other documents

Finding LFV-802Area: index / IndexWriter tryUpdateDocValue (tryModifyDocument doc-id validation, doc-values update buffer)Priority: lowImpact: data corruptionNovelty: new

Finding page for LFV-802

AI-assisted finding, confirmed by automated checks, not yet triaged by a human Lucene committer. This site files nothing upstream.

What it shows

You call IndexWriter#tryUpdateDocValue with an NRT reader and a doc id outside [0, reader.maxDoc()), for example 8 or 9 on an 8-document reader, 12 on a 10-document reader, or -1 on a 4-document leaf reader. You expect the call to be rejected, as the same reader rejects such an id ('docID must be >= 0 and < maxDoc', IllegalArgumentException), or at least to leave every other document alone. Instead, with assertions disabled (and for the negative leaf-reader id even with them enabled) it returns a sequence number > 0, which the javadoc says means the update succeeded, and writes the value to or soft-deletes a different live document (8 -> doc 0, 9 -> doc 1, -1 -> doc 3), or commits a doc-values entry for nonexistent doc 12 that CheckIndex accepts and that forceMerge turns into every document of the next segment carrying its predecessor's value (b0=777, b1=1000, ..., b9=1008; 1009 is lost).

The test shows that IndexWriter#tryUpdateDocValue on a 4-doc NRT leaf reader with docID -1 reports success and updates a different document.

Expected vs actual

Expected: docID -1 is rejected or changes nothing (doc 3 keeps v=3); actual: it returns seqNo 7 and doc 3 gets v=777, with -ea and -da.

Files

• src/org/apache/lucene/index/TestTryUpdateDocValueNegativeDocId.java (JUnit test)

Run it

• Tested on Lucene main e1faeba08bde (2026-11-02): still reproduces.
• Tested on Lucene main 645d4fe14a20 (2026-10-28): reproduced.
• Recorded outcome of run 1 on Lucene main 645d4fe14a20: 1 test(s) run, 1 failed.
• How to read the outcome: a failing test is the finding reproducing (the failure message states expected against actual).
• Seeds: a rerun with the same seed replays the same random choices. Assertions off (-da -dsa -Dtests.asserts=false) is the production-like setting.

# Lucene checkout at the tested commit, built with: ./gradlew --no-daemon assemble   (JDK 25)
LUCENE=/path/to/lucene; V=12.0.0-SNAPSHOT
CP=$LUCENE/lucene/core/build/libs/lucene-core-$V.jar
CP=$CP:$LUCENE/lucene/codecs/build/libs/lucene-codecs-$V.jar
CP=$CP:$LUCENE/lucene/test-framework/build/libs/lucene-test-framework-$V.jar
CP=$CP:randomizedtesting-runner-2.9.2.jar:junit-4.13.2.jar:hamcrest-3.0.jar   # test-framework dependencies (Maven Central)
CP=$CP:junit-platform-console-standalone-6.1.3.jar   # JUnit Platform console launcher (Maven Central)

javac -d classes -cp "$CP" $(find src -name '*.java')

# run 1: assertions on, seed 80200001
java -ea -esa --add-modules jdk.incubator.vector --enable-native-access=ALL-UNNAMED -Dtests.seed=80200001 \
     -cp "classes:$CP" org.junit.platform.console.ConsoleLauncher \
     execute --select-class org.apache.lucene.index.TestTryUpdateDocValueNegativeDocId

Gradle alternative: copy the test into the matching module's src/test/ tree of the checkout and run ./gradlew -p lucene/<module> test --tests <class> -Ptests.seed=<seed> (add -Ptests.asserts=false for a run without assertions).

Feedback

Open an issue in lucene-ai-bug-hunt. Please do not open issues or pull requests in apache/lucene about this finding unless a Lucene committer agrees it should be filed.

Snapshot of 2026-11-04. AI-assisted; not yet triaged by a human Lucene committer. Feedback: open an issue in lucene-ai-bug-hunt.