diff --git a/media/parsers/h265_parser_unittest.cc b/media/parsers/h265_parser_unittest.cc
index 62e00608e5492..640fa08f0574d 100644
--- a/media/parsers/h265_parser_unittest.cc
+++ b/media/parsers/h265_parser_unittest.cc
@@ -634,4 +634,79 @@ TEST_F(H265ParserTest, ValidSubLayerCount) {
   EXPECT_NE(H265Parser::kOk, parser.ParseVPS(&unused_vps_id));
 }
 
+// POC: H265Parser accepts CtbLog2SizeY=30 (spec max 6) and derived
+// max_transform_hierarchy_depth_{inter,intra}=28 (spec max 4),
+// diff_cu_qp_delta_depth=27 (spec max 3),
+// log2_parallel_merge_level_minus2=28 (spec max 4). These reach the
+// VAAPI/V4L2 driver verbatim with no re-clamp (CWE-1284).
+TEST_F(H265ParserTest, AcceptsOutOfSpecCtbLog2SizeY) {
+  constexpr auto kStream = std::to_array<unsigned char>({
+      // VPS
+      0x00, 0x00, 0x00, 0x01, 0x40, 0x01, 0x0c, 0x01, 0xff, 0xff, 0x01, 0x60,
+      0x00, 0x00, 0x03, 0x00, 0x80, 0x00, 0x00, 0x03, 0x00, 0x00, 0x03, 0x00,
+      0x5d, 0xac, 0x09,
+      // SPS: log2_diff_max_min_luma_coding_block_size=27 -> CtbLog2SizeY=30
+      0x00, 0x00, 0x00, 0x01, 0x42, 0x01, 0x01, 0x01, 0x60, 0x00, 0x00, 0x03,
+      0x00, 0x80, 0x00, 0x00, 0x03, 0x00, 0x00, 0x03, 0x00, 0x5d, 0xa0, 0x0a,
+      0x08, 0x0f, 0x17, 0xae, 0x1c, 0x90, 0x3a, 0x1d, 0x08, 0x20,
+      // PPS: diff_cu_qp_delta_depth=27, log2_parallel_merge_level_minus2=28
+      0x00, 0x00, 0x00, 0x01, 0x44, 0x01, 0xc0, 0x72, 0x1c, 0xc0, 0x00, 0xe9,
+      // IDR_W_RADL
+      0x00, 0x00, 0x00, 0x01, 0x26, 0x01, 0xaf, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0,
+      0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0, 0xa0,
+  });
+  H265Parser parser;
+  parser.SetStream(kStream);
+
+  H265NALU nalu;
+  ASSERT_EQ(H265Parser::kOk, parser.AdvanceToNextNALU(&nalu));
+  ASSERT_EQ(nalu.nal_unit_type, H265NALU::VPS_NUT);
+  int vps_id;
+  ASSERT_EQ(H265Parser::kOk, parser.ParseVPS(&vps_id));
+
+  ASSERT_EQ(H265Parser::kOk, parser.AdvanceToNextNALU(&nalu));
+  ASSERT_EQ(nalu.nal_unit_type, H265NALU::SPS_NUT);
+  int sps_id;
+  // BUG: ParseSPS accepts CtbLog2SizeY=30. H.265 7.4.3.2.1 / Annex A
+  // require CtbLog2SizeY in [4,6]; ffmpeg rejects >6.
+  ASSERT_EQ(H265Parser::kOk, parser.ParseSPS(&sps_id));
+  const H265SPS* sps = parser.GetSPS(sps_id);
+  ASSERT_TRUE(sps);
+  EXPECT_EQ(0, sps->log2_min_luma_coding_block_size_minus3);
+  EXPECT_EQ(27, sps->log2_diff_max_min_luma_coding_block_size);  // spec max 3
+  EXPECT_EQ(30, sps->ctb_log2_size_y);                           // spec max 6
+  EXPECT_EQ(28, sps->max_transform_hierarchy_depth_inter);       // spec max 4
+  EXPECT_EQ(28, sps->max_transform_hierarchy_depth_intra);       // spec max 4
+
+  ASSERT_EQ(H265Parser::kOk, parser.AdvanceToNextNALU(&nalu));
+  ASSERT_EQ(nalu.nal_unit_type, H265NALU::PPS_NUT);
+  int pps_id;
+  ASSERT_EQ(H265Parser::kOk, parser.ParsePPS(nalu, &pps_id));
+  const H265PPS* pps = parser.GetPPS(pps_id);
+  ASSERT_TRUE(pps);
+  EXPECT_EQ(27, pps->diff_cu_qp_delta_depth);             // spec max 3
+  EXPECT_EQ(28, pps->log2_parallel_merge_level_minus2);   // spec max 4
+
+  ASSERT_EQ(H265Parser::kOk, parser.AdvanceToNextNALU(&nalu));
+  ASSERT_EQ(nalu.nal_unit_type, H265NALU::IDR_W_RADL);
+  H265SliceHeader shdr;
+  // The slice header also parses cleanly -> H265Decoder would call
+  // SubmitFrameMetadata() with these out-of-spec values, which the VAAPI/V4L2
+  // delegates copy verbatim into uint8_t/__u8 driver fields.
+  ASSERT_EQ(H265Parser::kOk, parser.ParseSliceHeader(nalu, &shdr, nullptr));
+
+  fprintf(stderr,
+          "[POC] H265Parser accepted out-of-spec values:\n"
+          "  ctb_log2_size_y=%d (spec max 6)\n"
+          "  log2_diff_max_min_luma_coding_block_size=%d (spec max 3)\n"
+          "  max_transform_hierarchy_depth_inter=%d (spec max 4)\n"
+          "  max_transform_hierarchy_depth_intra=%d (spec max 4)\n"
+          "  diff_cu_qp_delta_depth=%d (spec max 3)\n"
+          "  log2_parallel_merge_level_minus2=%d (spec max 4)\n",
+          sps->ctb_log2_size_y, sps->log2_diff_max_min_luma_coding_block_size,
+          sps->max_transform_hierarchy_depth_inter,
+          sps->max_transform_hierarchy_depth_intra,
+          pps->diff_cu_qp_delta_depth, pps->log2_parallel_merge_level_minus2);
+}
+
 }  // namespace media