From 4980c011b86b209755d4b9ff536d957d18ae60b7 Mon Sep 17 00:00:00 2001 From: Christoph Wille Date: Tue, 25 Aug 2026 11:40:54 +0200 Subject: [PATCH] Never size bundle entry decompression from the manifest's declared size A single-file bundle manifest is attacker-controlled. Opening a compressed entry pre-allocated a MemoryStream of the declared decompressed size through an unchecked long-to-int cast, then inflated the whole deflate stream before comparing lengths. A few-byte payload declaring ~2 GB thus forced a ~2 GB allocation up front, sizes at or above 2 GB wrapped to a negative capacity, and a decompression bomb was expanded in full before the mismatch was noticed (CWE-789, CWE-197). Grow the buffer only with bytes the deflate stream actually produces and stop reading one byte past the declared size, which already proves the entry corrupt. Reject declared sizes that cannot fit a single in-memory buffer as invalid bundle data. Entry offsets need no extra check: the UnmanagedMemoryStream over the mapping already validates them against the view length. Assisted-by: Claude:claude-fable-5:Claude Code --- ICSharpCode.ILSpyX/LoadedPackage.cs | 21 ++- ILSpy.Tests/LoadedPackageBundleTests.cs | 192 ++++++++++++++++++++++++ 2 files changed, 211 insertions(+), 2 deletions(-) create mode 100644 ILSpy.Tests/LoadedPackageBundleTests.cs diff --git a/ICSharpCode.ILSpyX/LoadedPackage.cs b/ICSharpCode.ILSpyX/LoadedPackage.cs index dfeecf797..35cc5368f 100644 --- a/ICSharpCode.ILSpyX/LoadedPackage.cs +++ b/ICSharpCode.ILSpyX/LoadedPackage.cs @@ -239,10 +239,27 @@ namespace ICSharpCode.ILSpyX } else { + // entry.Size comes straight from the manifest and is not trusted: it must never + // size an allocation, and decompression must not run past it. A size that does + // not fit a single in-memory buffer cannot be a real entry either. + if (entry.Size < 0 || entry.Size > int.MaxValue) + { + throw new InvalidDataException($"Corrupted single-file entry '{entry.RelativePath}'. Declared decompressed size '{entry.Size}' is not valid."); + } Stream compressedStream = new UnmanagedMemoryStream(view.SafeMemoryMappedViewHandle, entry.Offset, entry.CompressedSize); using var deflateStream = new DeflateStream(compressedStream, CompressionMode.Decompress); - Stream decompressedStream = new MemoryStream((int)entry.Size); - deflateStream.CopyTo(decompressedStream); + // Grows only with the bytes that actually come out of the deflate stream. Reading + // one byte past the declared size is enough to prove the entry corrupt, so a + // decompression bomb stops there instead of being inflated in full. + Stream decompressedStream = new MemoryStream(); + byte[] buffer = new byte[81920]; + long remaining = entry.Size + 1; + int read; + while (remaining > 0 && (read = deflateStream.Read(buffer, 0, (int)Math.Min(buffer.Length, remaining))) > 0) + { + decompressedStream.Write(buffer, 0, read); + remaining -= read; + } if (decompressedStream.Length != entry.Size) { throw new InvalidDataException($"Corrupted single-file entry '{entry.RelativePath}'. Declared decompressed size '{entry.Size}' is not the same as actual decompressed size '{decompressedStream.Length}'."); diff --git a/ILSpy.Tests/LoadedPackageBundleTests.cs b/ILSpy.Tests/LoadedPackageBundleTests.cs new file mode 100644 index 000000000..3301f1037 --- /dev/null +++ b/ILSpy.Tests/LoadedPackageBundleTests.cs @@ -0,0 +1,192 @@ +// Copyright (c) 2026 Christoph Wille +// +// Permission is hereby granted, free of charge, to any person obtaining a copy of this +// software and associated documentation files (the "Software"), to deal in the Software +// without restriction, including without limitation the rights to use, copy, modify, merge, +// publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons +// to whom the Software is furnished to do so, subject to the following conditions: +// +// The above copyright notice and this permission notice shall be included in all copies or +// substantial portions of the Software. +// +// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, +// INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR +// PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE +// FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR +// OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER +// DEALINGS IN THE SOFTWARE. + +using System; +using System.Collections.Generic; +using System.IO; +using System.IO.Compression; +using System.Linq; +using System.Text; + +using ICSharpCode.ILSpyX; + +using NUnit.Framework; + +namespace ICSharpCode.ILSpy.Tests; + +/// +/// The sizes in a single-file bundle manifest are attacker-controlled. These tests pin down +/// that opening a compressed entry never allocates based on the declared size and stops +/// inflating as soon as the data exceeds it, so a small bundle cannot become a multi-gigabyte +/// allocation. +/// +[TestFixture] +public class LoadedPackageBundleTests +{ + // The 32-byte bundle signature (SHA-256 of ".net core bundle"), as in SingleFileBundle.IsBundle. + static readonly byte[] Signature = new byte[] { + 0x8b, 0x12, 0x02, 0xb9, 0x6a, 0x61, 0x20, 0x38, + 0x72, 0x7b, 0x93, 0x02, 0x14, 0xd7, 0xa0, 0x32, + 0x13, 0xf5, 0xb9, 0xe6, 0xef, 0xae, 0x33, 0x18, + 0xee, 0x3b, 0x2d, 0xce, 0x24, 0xb3, 0x6a, 0xae + }; + + readonly List tempFiles = new(); + + [TearDown] + public void DeleteTempFiles() + { + // The memory-mapped view stays alive as long as the bundle entries do, so the file + // can only be deleted once those have been collected. + GC.Collect(); + GC.WaitForPendingFinalizers(); + foreach (var file in tempFiles) + { + try + { + File.Delete(file); + } + catch (IOException) + { + // best effort; the temp directory is cleaned up by the OS eventually + } + } + } + + [Test] + public void CompressedEntry_WithMatchingDeclaredSize_RoundTrips() + { + byte[] content = Enumerable.Range(0, 10_000).Select(i => (byte)(i * 7)).ToArray(); + var bundle = WriteBundle(new BundleFile("lib.dll", Deflate(content), content.Length)); + + var package = LoadedPackage.FromBundle(bundle); + + Assert.That(package, Is.Not.Null); + var entry = package!.Entries.Single(); + Assert.That(entry.TryGetLength(), Is.EqualTo(content.Length)); + using var stream = entry.TryOpenStream(); + Assert.That(ReadAll(stream!), Is.EqualTo(content)); + } + + [Test] + public void UncompressedEntry_RoundTrips() + { + byte[] content = Encoding.ASCII.GetBytes("plain content"); + var bundle = WriteBundle(new BundleFile("plain.dll", content, content.Length, Compressed: false)); + + var package = LoadedPackage.FromBundle(bundle); + + using var stream = package!.Entries.Single().TryOpenStream(); + Assert.That(ReadAll(stream!), Is.EqualTo(content)); + } + + [Test] + public void CompressedEntry_DeclaredSizeBeyondInt32_IsRejectedAsInvalidData() + { + // A declared size that does not fit an int used to be truncated to a negative + // MemoryStream capacity; any size that cannot be held in memory must be reported as + // corrupt bundle data instead. + byte[] content = new byte[100]; + var bundle = WriteBundle(new BundleFile("huge.dll", Deflate(content), DeclaredSize: 3L * 1024 * 1024 * 1024)); + + var entry = LoadedPackage.FromBundle(bundle)!.Entries.Single(); + + Assert.Throws(() => entry.TryOpenStream()); + } + + [Test] + public void CompressedEntry_InflatingBeyondDeclaredSize_StopsEarly() + { + // A decompression bomb: a few kilobytes that inflate to 32 MB, declared as 16 bytes. + // Decompression must stop as soon as the declared size is exceeded rather than + // inflating everything first and comparing lengths afterwards, so the memory the + // attacker can force is bounded by what the manifest declares, not by the bomb. + const int inflatedSize = 32 * 1024 * 1024; + var bundle = WriteBundle(new BundleFile("bomb.dll", Deflate(new byte[inflatedSize]), DeclaredSize: 16)); + var entry = LoadedPackage.FromBundle(bundle)!.Entries.Single(); + + long allocatedBefore = GC.GetAllocatedBytesForCurrentThread(); + Assert.Throws(() => entry.TryOpenStream()); + long allocated = GC.GetAllocatedBytesForCurrentThread() - allocatedBefore; + + Assert.That(allocated, Is.LessThan(4 * 1024 * 1024), "opening the entry inflated far past its declared size"); + } + + sealed record BundleFile(string RelativePath, byte[] StoredBytes, long DeclaredSize, bool Compressed = true); + + static byte[] Deflate(byte[] content) + { + var ms = new MemoryStream(); + using (var deflate = new DeflateStream(ms, CompressionLevel.Optimal, leaveOpen: true)) + { + deflate.Write(content); + } + return ms.ToArray(); + } + + static byte[] ReadAll(Stream stream) + { + var ms = new MemoryStream(); + stream.CopyTo(ms); + return ms.ToArray(); + } + + /// + /// Writes a minimal version-6 single-file bundle: the stored file bytes, the manifest, + /// the 8-byte manifest offset and the bundle signature, in that order. + /// + string WriteBundle(params BundleFile[] files) + { + var ms = new MemoryStream(); + var writer = new BinaryWriter(ms, Encoding.UTF8, leaveOpen: true); + var offsets = new long[files.Length]; + for (int i = 0; i < files.Length; i++) + { + offsets[i] = ms.Position; + writer.Write(files[i].StoredBytes); + } + + long manifestOffset = ms.Position; + writer.Write(6u); // MajorVersion (v6 adds the compressed size field) + writer.Write(0u); // MinorVersion + writer.Write(files.Length); // FileCount + writer.Write("test-bundle"); // BundleID + writer.Write(0L); // DepsJsonOffset + writer.Write(0L); // DepsJsonSize + writer.Write(0L); // RuntimeConfigJsonOffset + writer.Write(0L); // RuntimeConfigJsonSize + writer.Write(0UL); // Flags + for (int i = 0; i < files.Length; i++) + { + writer.Write(offsets[i]); // Offset + writer.Write(files[i].DeclaredSize); // Size + writer.Write(files[i].Compressed ? files[i].StoredBytes.Length : 0L); // CompressedSize + writer.Write((byte)1); // FileType.Assembly + writer.Write(files[i].RelativePath); + } + + writer.Write(manifestOffset); + writer.Write(Signature); + writer.Flush(); + + string path = Path.Combine(Path.GetTempPath(), "ILSpyBundleTest-" + Guid.NewGuid().ToString("N") + ".exe"); + File.WriteAllBytes(path, ms.ToArray()); + tempFiles.Add(path); + return path; + } +}