Secrets briefly visible in /proc cmdline via base64 -d subprocess

[mrjf]

Summary

Secrets are written into env.sh as export VAR=\$(echo 'base64...' | base64 -d). The base64-encoded value is visible in /proc/[pid]/cmdline of the base64 subprocess for the duration of decoding.

Where

packages/runtime/src/band-server.ts:519-522

for (const [key, value] of Object.entries(req.secrets ?? {})) {
  const b64 = Buffer.from(value).toString("base64");
  envLines.push(\`export \${key}=\$(echo '\${b64}' | base64 -d)\`);
}

Impact

Inside the sandbox, any process walking /proc/[pid]/cmdline during script startup sees the encoded secret. The decode is trivial. Also, if a script enables set -x, the decoded secret is printed to stderr.

This is limited to processes the band-runner uid can see, but /proc is fully mounted (see #28), so any subprocess of the script can observe sibling subprocess cmdlines.

Fix sketch

Write the secret to a 0600 file in the workdir and read it without command substitution:

export VAR=\"\$(< \$WORKDIR/secrets/VAR)\"

Or use bash read from a heredoc to avoid the file:

read -r VAR <<< \"actual-secret-value\"
export VAR

Or pass secrets to the script's stdin / a pipe, never via the env.sh that becomes a process argument.