An out-of-bounds write vulnerability was found in GStreamer's H.266/VVC PPS picture partition parser in gst-plugins-bad. In the multi-slice-in-tile processing of gst_h266_parser_parse_picture_partition() (gsth266parser.c), the loop iterates without checking that the slice index stays within bounds, writing past three fixed-size arrays (slice_height_in_ctus, slice_top_left_ctu_x, slice_top_left_ctu_y) in the GstH266PPS structure. While the initial proof-of-concept demonstrated a 4-byte out-of-bounds write, the code permits larger writes across multiple iterations. A crafted H.266/VVC media file can trigger this vulnerability.