💣 Mitigate chain of supply attacks
👌 Verify your curl scripts and executables

---

🤔 What is it?

preflight helps you verify scripts and executables to mitigate chain of supply attacks such as the recent Codecov hack.

🎁 Getting Preflight

First of all, it's the chicken and the egg. How do you pull a legit preflight binary from us without verifying it with preflight? having that preflight is solving this exact problem?

The best way, is that you grab the source, compile it yourself, and use your own binary which you put in a place that you trust. People usually have several options of how to do that safely:

• Put it on your own S3 bucket
• Drop it on your own Artifactory or similar
• Push it directly into your repos (it should be as small as 4mb, and almost never change so, Git should work nicely with it)
• Build from source into your containers directly:

FROM golang:1.16-alpine AS preflight_builder
RUN apk add --no-cache git
WORKDIR /builds
RUN GOBIN=`pwd` go get -u github.com/spectralops/preflight

# Build from a bare image, copy built binary
FROM alpine:3.9 
RUN apk add ca-certificates
COPY --from=preflight_builder /builds/preflight /usr/local/bin

# use preflight as you wish
RUN curl https://.. | preflight run <digest>

If you want to just get started quickly on your workstation, you can download a release or install preflight with homebrew:

$ brew tap spectralops/tap && brew install preflight

🚀 Quick Run

Someone changed the script or binary you're running. Abort!

$ curl -L https://XXX | preflight run sha256=1ce...2244a6e86
⌛️ Preflight starting
❌ Preflight failed:
Digest does not match.

Expected:
<...>

Actual: 
<...>
  
   Information:
   It is recommended to inspect the modified file contents.

A hash is verified, but it is actually vulnerable. Abort!

$ curl -L https://XXX | preflight run sha256=1ce...2244a6e86
⌛️ Preflight starting using file lookup: malshare.current.sha256.txt
❌ Preflight failed: Digest matches but marked as vulnerable.
   Digest matches but marked as vulnerable.

Information:
  Vulnerability: Hash was found in a vulnerable digest list
  More: malshare.current.sha256.txt

All ok, let's fly.

$ curl -L https://XXX | preflight run sha256=1ce...2244a6e86
⌛️ Preflight starting
✅ Preflight verified

... actual script output ...

✨ Examples

Github action

You can install Preflight with a Github action, or use it like this:

   - name: Setup Preflight
     uses: spectralops/setup-preflight@v1

And now, you have a preflight binary to play with.

⛳ Running codecov safely in your CI

First, let's create a hash (before creating it, review the script manually and see that it's not doing anything funny):

$ curl -s https://codecov.io/bash | ./preflight create
sha256=d6aa3207c4908d123bd8af62ec0538e3f2b9f257c3de62fad4e29cd3b59b41d9

Now, we're going to take

sha256=d6aa3207c4908d123bd8af62ec0538e3f2b9f257c3de62fad4e29cd3b59b41d9

And use this to secure our pulls from Codecov. In this case, preflight is checked safely into your repo under ci/preflight.

---

BEFORE (insecure):

steps:
   - curl -s https://codecov.io/bash | sh

AFTER (safe, yay!):

steps:
   - curl -s https://codecov.io/bash | ./ci/preflight run sha256=d6aa3207c4908d123bd8af62ec0538e3f2b9f257c3de62fad4e29cd3b59b41d9

---

⛳ Building Docker images in a secure way

It's recommended to use preflight when you're building Docker images, and are installing via curl | sh scripts that vendors give you.

Before:

FROM alpine:3.9 
RUN apk add ca-certificates
RUN apk add curl coreutils

RUN cd /opt && curl -L https://istio.io/downloadIstio | ISTIO_VERSION=1.7.2 sh

After (securely building preflight from source + validating Istio with preflight):

FROM golang:1.16-alpine AS preflight_builder

RUN apk add --no-cache git
WORKDIR /builds

RUN GOBIN=`pwd` go get -u github.com/spectralops/preflight

# Build from a bare image, copy built binary
FROM alpine:3.9 
RUN apk add ca-certificates
RUN apk add curl coreutils

COPY --from=preflight_builder /builds/preflight /usr/local/bin

# create a hash with:
# curl -L https://istio.io/downloadIstio | preflight create
RUN cd /opt && curl -L https://istio.io/downloadIstio | \
    ISTIO_VERSION=1.7.2 \
    preflight run sha256=e826fb57c6705cca0b6464edf4c1701d4bd5fd5879f5820fca78941c0a83ce64

Using preflight we're also getting a nice confirmation badge during the build process:

... docker build log...

⌛️ Preflight starting
✅ Preflight verified

Downloading istio-1.7.2 from https://github.com/istio/istio/releases/download/1.7.2/istio-1.7.2-linux-amd64.tar.gz ...

Istio 1.7.2 Download Complete!

💡 Dealing with changing runnables & auto updates

When updating an old binary or script to a new updated version, there will be at least two (2) valid digests "live" and just replacing the single digest used will fail for the older runnable which may still be running somewhere.

$ preflight <hash list|https://url/to/hash-list>

To support updates and rolling/auto updates of scripts and binaries we basically need to validate against <old hash> + <new hash> at all times, until everyone upgrades to the new script. Preflight validates against a list of hashes or better, give it a live URL of valid hashes and it will validate against it.

curl .. | ./ci/preflight run sha256=d6aa3207c4908d123bd8af62ec0538e3f2b9f257c3de62fad4e29cd3b59b41d9,sha256=<new hash>,...

Or to a live URL:

curl .. | ./ci/preflight run https://dl.example.com/hashes.txt

Use this when:

• Use multiple digests verbatim, when your runnables change often, but not too often
• Use a URL when your runnables change often. Remember to follow the chain of trust. This will now mean that:
  • Your hash list URL is now a source of trust
  • Visually: we're swapping the chain of trust like so curl <foreign trust> | ./ci/preflight <own trust>

🏃 Running scripts and binaries

Piping:

$ curl -s https://example.com/some-script | preflight run sha256=d6aa3207c4<...>b4

Executables:

$ preflight run sha256=d6aa3207c4<...>b4 ./my-script.sh

🔎 Checking scripts and binaries

Piping:

$ curl -s https://example.com/some-script | preflight check sha256=d6aa3207c4<...>b4 | sh

Not that preflight check is built in a way that you could continue to pipe to the next process:

• If a check passes, the checked script or binary content will be dumped to STDOUT
• If a check fails, you'll get an exit(1), and an error message

Executables:

$ preflight check sha256=d6aa3207c4<...>b4 ./my-script.sh

In this case:

• If a check passes, you'll get an exit(0) and no output (so you can compose with other tooling)
• If a check fails, you'll get an exit(1) and an error message

📍 Creating new hashes

You can easily create new hashes with preflight. The default is a SHA256 hash, but you could also create a sha256, sha1, and md5 hash.

$ preflight create test.sh
sha256=fe6d02cf15642ff8d5f61cad6d636a62fd46a5e5a49c06733fece838f5fa9d85

Though not recommended, you can create other kinds (weaker kinds) of hashes for legacy/compatibility reasons:

$ preflight create test.sh --digest md5
md5=cb62874fea06458b2b0cabf2322c9d55

🙈 Using optional malware lookup

preflight comes with lookup providers, which is optional -- you can enable them by using environment variables:

File Lookup

You can download a daily list of malware signatures from malshare.com or any equivalent service. Here is a direct link to such a list.

Then:

• Set PF_FILE_LOOKUP=./path/to/text/file

With this configured preflight will search for all digest types in this file before approving.

Here is a full example for your CI, combining preflight with Malshare:

env:
   PF_FILE_LOOKUP: malshare.current.sha256.txt

steps: 
- wget https://www.malshare.com/daily/malshare.current.sha256.txt
- curl https://... | preflight <sha>

Result:

$ PF_FILE_LOOKUP=malshare.current.sha256.txt preflight run fe6d02cf15642ff8d5f61cad6d636a62fd46a5e5a49c06733fece838f5fa9d85 test.sh
⌛️ Preflight starting using file lookup: malshare.current.sha256.txt
❌ Preflight failed: Digest matches but marked as vulnerable.

Information:
  Vulnerability: Hash was found in a vulnerable digest list
  More: malshare.current.sha256.txt

VirusTotal Lookup

You can use the virus total community API access to lookup your hashes.

• Set PF_VT_TOKEN=your-virustotal-api-key

With this configured preflight will automatically create the VirusTotal lookup provider and validate digest with it.

Here is a full example for your CI, combining preflight with VirusTotal:

env:
   PF_VT_TOKEN: {{secrets.PF_VT_TOKEN}}

steps: 
- curl https://... | preflight <sha>

Result:

$ PF_VT_TOKEN=xxx preflight check e86d4eb1e888bd625389f2e50644be67a6bdbd77ff3bceaaf182d45860b88d80 kx-leecher.exe
⌛️ Preflight starting using VirusTotal
❌ Preflight failed: Digest matches but marked as vulnerable.

Information:
  Vulnerability: VirusTotal stats - malicious: 40, suspicious 0
  More: https://www.virustotal.com/gui/file/e86d4eb1e888bd625389f2e50644be67a6bdbd77ff3bceaaf182d45860b88d80/detection

Other lookup types?

We've established that a file lookup is universal and general enough to be useful to everyone. However, you might prefer your own vendor, or a service such as VirusTotal -- preflight's architecture is pluggable and we're accepting pull requests.

Thanks

To all Contributors - you make this happen, thanks!

Copyright

Copyright (c) 2021 @jondot. See LICENSE for further details.