yawkat LZ4 Java provides LZ4 compression for Java. Prior to 1.11.4, net.jpountz.lz4.LZ4BlockInputStream configured with stopOnEmptyBlock set to false handles each well-formed empty LZ4Block by recursively calling refill(), allowing a long sequence of empty blocks in an attacker-controlled compressed stream to exhaust the decoding thread's stack and throw StackOverflowError. The default stopOnEmptyBlock setting is true and is not affected, and the issue does not cause memory corruption. This issue is fixed in version 1.11.4.

Affected: Maven: at.yawk.lz4:lz4-java, Maven: org.lz4:lz4-java

### Summary

When `LZ4BlockInputStream` is configured with `stopOnEmptyBlock = false` (the mode for reading concatenated block streams), it handles each empty block by calling `refill()` recursively. A long run of empty blocks exhausts the thread stack and throws `StackOverflowError` out of `read()` or `skip()`.

### Details

In `net.jpountz.lz4.LZ4BlockInputStream.refill()`:

```java if (originalLen == 0 && compressedLen == 0) { if (check != 0) { throw new IOException("Stream is corrupted"); } if (!stopOnEmptyBlock) { refill(); } else { finished = true; } return; } ```

Each well-formed empty block is 21 bytes and adds one stack frame, with no limit on nesting depth. In local testing, around 10,000 to 100,000 consecutive empty blocks (about 210 KB to 2.1 MB, depending on JIT state and thread stack size) threw `StackOverflowError`. `StackOverflowError` is an `Error`, not an `IOException`, so callers that only handle I/O errors for corrupt input don't catch it.

### Impact

Applications that decode attacker-controlled `LZ4Block` streams with `LZ4BlockInputStream.newBuilder().withStopOnEmptyBlock(false)` or the deprecated `LZ4BlockInputStream(InputStream, boolean)` constructor can have the decoding thread fail with `StackOverflowError`. The default configuration (`stopOnEmptyBlock = true`) is not affected. There is no memory corruption. Availability impact only.

### Patch

Fixed in lz4-java 1.11.4. Empty blocks are now skipped in a loop instead of by r…

Affected: Ubuntu:20.04:LTS: lz4-java, Ubuntu:22.04:LTS: lz4-java, Ubuntu:24.04:LTS: lz4-java, Ubuntu:26.04:LTS: lz4-java

(yawkat LZ4 Java provides LZ4 compression for Java. Prior to 1.11.4, ne ...)