diff -up libwebp-0.3.0/src/mux/muxread.c.rhbz-1956919 libwebp-0.3.0/src/mux/muxread.c

--- libwebp-0.3.0/src/mux/muxread.c.rhbz-1956919	2021-05-27 09:52:07.953914353 +0200

+++ libwebp-0.3.0/src/mux/muxread.c	2021-05-27 09:52:59.325863123 +0200

@@ -118,6 +118,7 @@ static int MuxImageParse(const WebPChunk

         wpi->is_partial_ = 1;  // Waiting for a VP8 chunk.

         break;

       case WEBP_CHUNK_IMAGE:

+        if (wpi->img_ != NULL) goto Fail;  // Only 1 image chunk allowed.

         if (ChunkSetNth(&subchunk, &wpi->img_, 1) != WEBP_MUX_OK) goto Fail;

         wpi->is_partial_ = 0;  // wpi is completely filled.

         break;