Fix

src/ImageSharp/Formats/Jpeg/JpegDecoderCore.cs

@@ -472,7 +472,7 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
                     : JpegColorSpace.Cmyk;
             }
 
-            JpegThrowHelper.ThrowInvalidImageContentException($"Unsupported color mode. Supported component counts 1, 3, and 4; found {componentCount}");
+            JpegThrowHelper.ThrowNotSupportedComponentCount(componentCount);
             return default;
         }
 
@@ -998,6 +998,14 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
             // 1 byte: Number of components
             byte componentCount = this.temp[5];
 
+            // Validate: componentCount more than 4 can lead to a buffer overflow during stream
+            // reading so we must limit it to 4
+            // We do not support jpeg images with more than 4 components anyway
+            if (componentCount > 4)
+            {
+                JpegThrowHelper.ThrowNotSupportedComponentCount(componentCount);
+            }
+
             this.Frame = new JpegFrame(frameMarker, precision, frameWidth, frameHeight, componentCount);
 
             remaining -= length;

src/ImageSharp/Formats/Jpeg/JpegThrowHelper.cs

@@ -45,5 +45,8 @@ namespace SixLabors.ImageSharp.Formats.Jpeg
 
         [MethodImpl(InliningOptions.ColdPath)]
         public static void ThrowDimensionsTooLarge(int width, int height) => throw new ImageFormatException($"Image is too large to encode at {width}x{height} for JPEG format.");
+
+        [MethodImpl(InliningOptions.ColdPath)]
+        public static void ThrowNotSupportedComponentCount(int componentCount) => throw new NotSupportedException($"Images with {componentCount} components are not supported.");
     }
 }