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Feature option values are changed before install.sh sees them: quotes are stripped, and $… is expanded or executed #1324
Description
Problem
A Feature can receive a different string option value from the one configured in
devcontainer.json. Quotes are removed, $VAR is expanded, $(…) and backticks are executed, and backslashes are consumed. The build still succeeds, so nothing
signals that the value changed.
Repro (devcontainer CLI 0.89.0)
A local Feature with one string option, value, whose install.sh prints it:
#!/bin/sh
printf '%s\n' "$VALUE""features": { "./echo-opt": { "value": "say \"hi\" to $HOME as $(id -un)" } }- Expected:
say "hi" to $HOME as $(id -un) - Actual:
say hi to /root as root
A value with a space inside quotes, such as A="two words", fails the build instead,
with devcontainer-features.env: line 1: words: not found.
Cause
getFeatureEnvVariables (src/spec-node/containerFeatures.ts) writes each option as
NAME="value" without escaping. The install wrapper then sources the file
(set -a; . ./devcontainer-features.env), so the shell interprets the value. Issue #148
and PR #149 fixed this for spaces, but not for ", $, backticks or \.
Suggested fix
Write each value in single quotes, with ' escaped as '\''. That's what
escapeQuotesForShell already does for the wrapper's Options echo. This changes
behaviour for anyone relying on $ being expanded in option values today.
Activity
feat(container-env): add per-device environment variables Feature (#29)
laverdet commentedon Oct 27, 2026
I ran into this today. I was very surprised to see a basic shell escaping issue in a project of this importance. Here's the line in all its naive glory.
cli/src/spec-node/containerFeatures.ts
Lines 410 to 413 in 1245d72
We can actually workaround it in a most terrible way by breaking out of double quotes into single quotes, and then escaping single quotes in bash style (
'\''). From the report this would become:I might even go so far as to report this as a security issue. This would allow someone to execute arbitrary code in the container using only a option flag as an attack vector. Option flags are not considered as shell execution vectors so this would be surprising to someone who placed user input in this field.