This article will describe how to download an image from a (docker) container registry.

Manual Download of Container Images with wget and curl

Intro

Remember the good `'ol days when you could just download software by visiting a website and click "download"?

Even apt and yum repositories were just simple HTTP servers that you could just curl (or wget) from. Using the package manager was, of course, more secure and convenient -- but you could always just download packages manually, if you wanted.

But have you ever tried to curl an image from a container registry, such as docker? Well friends, I have tried. And I have the scars to prove it.

It was a remarkably complex process that took me weeks to figure-out. Lucky you, this article will break it down.

Examples

Specifically, we'll look at how to download files from two OCI registries.

1. Docker Hub
2. GitHub Packages

Terms

First, here's some terminology used by OCI

1. OCI - Open Container Initiative
2. blob - A "blob" in the OCI spec just means a file
3. manifest - A "manifest" in the OCI spec means a list of files

Prerequisites

This guide was written in 2024, and it uses the following software and versions:

1. debian 12 (bookworm)
2. curl 7.88.1
3. OCI Distribution Spec v1.1.0 (which, unintuitively, uses the '/v2/' endpoint)

Of course, you'll need 'curl' installed. And, to parse json, 'jq' too.

sudo apt-get install curl jq

What is OCI?

OCI stands for Open Container Initiative.

OCI was originally formed in June 2015 for Docker and CoreOS. Today it's a wider, general-purpose (and annoyingly complex) way that many projects host files (that are extremely non-trivial to download).

One does not simply download a file from an OCI-complianet container registry. You must:

1. Generate an authentication token for the API
2. Make an API call to the registry, requesting to download a JSON "Manifest"
3. Parse the JSON Manifest to figure out the hash of the file that you want
4. Determine the download URL from the hash
5. Download the file (which might actually be many distinct file "layers")

One does not simply download from a container registry

In order to figure out how to make an API call to the registry, you must first read (and understand) the OCI specs here.

• https://opencontainers.org/release-notices/overview/

OCI APIs

OCI maintains three distinct specifications:

1. image spec
2. runtime spec
3. distribution spec

OCI "Distribution Spec" API

To figure out how to download a file from a container registry, we're interested in the "distribution spec". At the time of writing, the latest "distribution spec" can be downloaded here:

• https://github.com/opencontainers/distribution-spec/releases/tag/v1.1.0
• https://github.com/opencontainers/distribution-spec/releases/download/v1.1.0/oci-distribution-spec-v1.1.0.pdf

The above PDF file defines a set of API endpoints that we can use to query, parse, and then figure out how to download a file from a container registry. The table from the above PDF is copied below:

In OCI, files are (cryptically) called "blobs". In order to figure out the file that we want to download, we must first reference the list of files (called a "manifest").

The above table shows us how we can download a list of files (manifest) and then download the actual file (blob).

Examples

Let's look at how to download files from a couple different OCI registries:

1. Docker Hub
2. GitHub Packages

Docker Hub

To see the full example of downloading images from docker hub, click here

GitHub Packages

To see the full example of downloading files from GitHub Packages, click here.

Why?

I wrote this article because many, many folks have inquired about how to manually download files from OCI registries on the Internet, but their simple queries are usually returned with a barrage of useless counter-questions: why the heck would you want to do that!?!

The answer is varied.

Some people need to get files onto a restricted environment. Either their org doesn't grant them permission to install software on the machine, or the system has firewall-restricted internet access -- or doesn't have internet access at all.

3TOFU

Personally, the reason that I wanted to be able to download files from an OCI registry was for 3TOFU.

Verifying Unsigned Releases with 3TOFU

Unfortunaetly, most apps using OCI registries are extremely insecure. Docker, for example, will happily download malicious images. By default, it doesn't do any authenticity verifications on the payloads it downloaded. Even if you manually enable DCT, there's loads of pending issues with it.

Likewise, the macOS package manager brew has this same problem: it will happily download and install malicious code, because it doesn't use cryptography to verify the authenticity of anything that it downloads. This introduces watering hole vulnerabilities when developers use brew to install dependencies in their CI pipelines.

My solution to this? 3TOFU. And that requires me to be able to download the file (for verification) on three distinct linux VMs using curl or wget.

⚠ NOTE: 3TOFU is an approach to harm reduction.

It is not wise to download and run binaries or code whose authenticity you cannot verify using a cryptographic signature from a key stored offline. However, sometimes we cannot avoid it. If you're going to proceed with running untrusted code, then following a 3TOFU procedure may reduce your risk, but it's better to avoid running unauthenticated code if at all possible.

Registry (ab)use

Container registries were created in 2013 to provide a clever & complex solution to a problem: how to package and serve multiple versions of simplified sources to various consumers spanning multiple operating systems and architectures -- while also packaging them into small, discrete "layers".

However, if your project is just serving simple files, then the only thing gained by uploading them to a complex system like a container registry is headaches. Why do developers do this?

In the case of brew, their free hosing provider (JFrog's Bintray) shutdown in 2021. Brew was already hosting their code on GitHub, so I guess someone looked at "GitHub Packages" and figured it was a good (read: free) replacement.

Many developers using Container Registries don't need the complexity, but -- well -- they're just using it as a free place for their FOSS project to store some files, man.

cross-posted from: https://lemmy.ml/post/18154572

All our servers and company laptops went down at pretty much the same time. Laptops have been bootlooping to blue screen of death. It's all very exciting, personally, as someone not responsible for fixing it.

Apparently caused by a bad CrowdStrike update.

Came across this guide and figured I'd share. Will be testing this out later this week.

Hi! I learned about AppArmor recently and I am setting up profiles for each of my applications on my server, but I'm not sure if I should also restrict python binary executable in local python environment for my django website, because AppArmor says: "is currently marked as a program that should not have its own profile.". Chat GPT says I should activate the environment, bypass the warning and create a profile, but I'm not sure, so I decided to ask if anyone knows better.

As I'm sure many others have encountered, within days of creating any user in O365, they start receiving spam, phishing, and solicitation emails. Some of these bad actors have shown a very clear pattern to me, so it leads me to believe a team of bad actors may have found access to our GAL and will make regular attempts to scam our employees. I'm of course, also curious how I might find that employees with minimal outside communications (external communications are with specific individuals at client companies.)

Unfortunately, I haven't much experience with SecOPs, so I'm curious if anyone more experienced can suggest some good tools to recommend for me to do some digging into this. Tool/app platform doesn't matter, I've got Windows, Mac, and Linux machines available to utilize for testing.

Hello c/sysadmin, and welcome to the Patch Megathread! I'm editing this post and leaving it up as a single catch-all sticky post for patch days for the time being, since we're not seeing enough activity to warrant new threads IMO. If someone wants to help moderate / curate content and actively create new patch day posts, please let me know and I'll add you to the mod team.

This is the place to talk about the latest patches, updates, and releases. We put this thread into place to help gather all the information about this month's updates: What is fixed, what broke, what got released and should have been caught in QA, etc. We do this both to keep clutter out of the community, and provide a singular resource to read.

While this thread is timed to coincide with Microsoft's Patch Tuesday, feel free to discuss any patches, updates, and releases, regardless of the company or product.

Remember the rules of safe patching:

• Deploy to a test/dev environment before prod.
• Deploy to a pilot/test group before the whole org.
• Have a plan to roll back if something doesn't work.
• Test, test, and test!

cross-posted from: https://lemmy.world/post/104228

I setup this community specifically because of the time I've spent over the years browsing and relying on reddit.com/r/sysadmin for sources of information on tips/tricks, security exploits & patches, outages, and yes even the ranting about how our jobs all suck. (I like mine, for what it's worth.)

Come on down, ask questions, post what the sysadmin community needs to know about, or head in to get either sympathy or chastisement about why you haven't left your job yet. 🤣

Want to be a mod? Let me know!

Please ignore