Backport #2501

Author: JimBobSquarePants

src/ImageSharp/Formats/Pbm/BufferedReadStreamExtensions.cs

@@ -29,7 +29,7 @@ public static void SkipWhitespaceAndComments(this BufferedReadStream stream)
                     {
                         innerValue = stream.ReadByte();
                     }
-                    while (innerValue != 0x0a);
+                    while (innerValue is not 0x0a and not -0x1);
 
                     // Continue searching for whitespace.
                     val = innerValue;

tests/ImageSharp.Tests/Formats/Pbm/PbmMetadataTests.cs

@@ -1,7 +1,9 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.IO;
+using SixLabors.ImageSharp.Formats;
 using SixLabors.ImageSharp.Formats.Pbm;
 
 using Xunit;
@@ -82,5 +84,15 @@ public void Identify_DetectsCorrectComponentType(string imagePath, PbmComponentT
             Assert.NotNull(bitmapMetadata);
             Assert.Equal(expectedComponentType, bitmapMetadata.ComponentType);
         }
+
+        [Fact]
+        public void Identify_HandlesCraftedDenialOfServiceString()
+        {
+            byte[] bytes = Convert.FromBase64String("UDEjWAAACQAAAAA=");
+            IImageInfo info = Image.Identify(bytes);
+            Assert.Equal(default, info.Size());
+            IImageFormat format = Configuration.Default.ImageFormatsManager.FindFormatByFileExtension("pbm");
+            Assert.Equal("PBM", format.Name);
+        }
     }
 }