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fix(careful): close three check-careful bypasses via real JSON extraction

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The grep-based command extractor stopped at the first escaped quote, so any
quoted argument truncated the command before the pattern checks ran —
`git commit -m "wip" && rm -rf /` was silently allowed. Replace it with a
python3/node JSON parse that fails CLOSED on unreadable payloads, add an
IFS/base64-to-shell obfuscation tripwire, and stop multi-line commands from
riding the single-line safe-exception whitelist (line-based grep would have
approved `rm -rf /` when a later line matched node_modules — a hazard the
real newline decoding exposed).

Contributed by @wtamminga (PR #2426; the -R hunk was dropped — it landed in
v1.61.0.0 — and output shapes updated to the nested hookSpecificOutput form).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
This commit is contained in:
Garry Tan
2026-08-14 15:38:16 -07:00
co-authored by Claude Fable 5
parent 7a7a83b73e
commit 5084f85e00
2 changed files with 155 additions and 18 deletions
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careful/bin/check-careful.sh
+69 -11
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@@ -9,16 +9,47 @@ set -euo pipefail
# Read stdin (JSON with tool_input)
INPUT=$(cat)
# Extract the "command" field value from tool_input
# Try grep/sed first (handles 99% of cases), fall back to Python for escaped quotes
CMD=$(printf '%s' "$INPUT" | grep -o '"command"[[:space:]]*:[[:space:]]*"[^"]*"' | head -1 | sed 's/.*:[[:space:]]*"//;s/"$//' || true)
# Extract the "command" field value from tool_input with a real JSON parser.
#
# The previous extractor was
# grep -o '"command"[[:space:]]*:[[:space:]]*"[^"]*"'
# whose [^"]* stops at the first escaped quote in the JSON string value. Any
# destructive command preceded by a quoted argument was therefore truncated
# away before the pattern checks ever ran:
#
# git commit -m "wip" && rm -rf / -> CMD='git commit -m \' -> allowed
# bash -c "rm -rf /" -> CMD='bash -c \' -> allowed
# echo "x"; rm -rf ~ -> CMD='echo \' -> allowed
#
# The python3 fallback never rescued these because CMD was non-empty, so the
# `[ -z "$CMD" ]` guard did not fire. Parse the payload properly instead, and
# fail CLOSED when it cannot be parsed at all — a hook that gates destructive
# commands must not allow-by-default on unreadable input.
#
# python3 is tried first because it ships with macOS and most Linux distros and
# is reliably on PATH in a hook environment; node is the fallback.
extract_cmd() {
if command -v python3 >/dev/null 2>&1; then
printf '%s' "$INPUT" | python3 -c 'import sys,json; d=json.loads(sys.stdin.read()); c=d.get("tool_input",{}).get("command",""); sys.stdout.write(c if isinstance(c,str) else "")' 2>/dev/null && return 0
fi
if command -v node >/dev/null 2>&1; then
printf '%s' "$INPUT" | node -e 'let s="";process.stdin.on("data",d=>s+=d).on("end",()=>{try{const j=JSON.parse(s);const c=(j&&j.tool_input&&j.tool_input.command)||"";process.stdout.write(typeof c==="string"?c:"")}catch(e){process.exit(3)}})' 2>/dev/null && return 0
fi
return 1
}
# Python fallback if grep returned empty (e.g., escaped quotes in command)
if [ -z "$CMD" ]; then
CMD=$(printf '%s' "$INPUT" | python3 -c 'import sys,json; print(json.loads(sys.stdin.read()).get("tool_input",{}).get("command",""))' 2>/dev/null || true)
set +e
CMD=$(extract_cmd)
EXTRACT_RC=$?
set -e
# No parser available, or the payload is not parseable JSON. Fail closed.
if [ "$EXTRACT_RC" -ne 0 ] && [ -n "$INPUT" ]; then
printf '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"ask","permissionDecisionReason":"[careful] Could not parse the tool payload to safety-check this command. Approve only if you know what it does."}}\n'
exit 0
fi
# If we still couldn't extract a command, allow
# Parsed fine, but there is genuinely no command field (non-Bash payload) — allow.
if [ -z "$CMD" ]; then
echo '{}'
exit 0
@@ -27,6 +58,23 @@ fi
# Normalize: lowercase for case-insensitive SQL matching
CMD_LOWER=$(printf '%s' "$CMD" | tr '[:upper:]' '[:lower:]')
# --- Shell-obfuscation tripwire ---
# Every check below inspects the command as a STRING, but bash executes what the
# string MEANS after expansion. ${IFS} holds the default field separator and
# contains no literal whitespace, so
#
# rm${IFS}-rf${IFS}/
#
# matches none of the `rm\s+` patterns while executing as a full recursive
# delete. The same holds for a command assembled by a base64 decode piped to a
# shell. Rather than try to out-parse bash, treat these splitting/decoding
# primitives as a reason to ask: they are vanishingly rare in commands a human
# actually means to run unattended.
if printf '%s' "$CMD" | grep -qE '\$\{IFS\}|\$IFS|\$\(echo[^)]*base64[^)]*\)|base64[[:space:]]+(-d|--decode)[^|]*\|[[:space:]]*(sh|bash)' 2>/dev/null; then
printf '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"ask","permissionDecisionReason":"[careful] Shell obfuscation detected (IFS word-splitting or base64-to-shell). Read the command carefully before approving."}}\n'
exit 0
fi
# --- Check for safe exceptions (one standalone rm of build artifacts) ---
# Match the complete command. Parsing only the last rm is unsafe because shell
# syntax or comments can hide an earlier destructive command, for example:
@@ -39,10 +87,20 @@ CMD_LOWER=$(printf '%s' "$CMD" | tr '[:upper:]' '[:lower:]')
# ENDS in a whitelisted suffix (`rm -rf $(./wipe-all)/node_modules`)
# cannot ride the whitelist. Plain $VAR expansion (no parenthesis) is
# still allowed.
if printf '%s' "$CMD" | grep -qE '^[[:space:]]*rm[[:space:]]+(-[a-zA-Z]*[rR][a-zA-Z]*[[:space:]]+|--recursive[[:space:]]+)(([^[:space:];&|#(`]*/)?(node_modules|\.next|dist|__pycache__|\.cache|build|\.turbo|coverage)[[:space:]]*)+$' 2>/dev/null; then
echo '{}'
exit 0
fi
# - multi-line commands never ride the whitelist: grep matches the anchored
# shape against EACH line, so `rm -rf /\nrm -rf node_modules` would be
# allowed by its second line. With the JSON-parser extraction the \n in
# the payload is a real newline (the old grep extractor kept it as two
# literal characters, which broke the anchored match by accident).
case "$CMD" in
*$'\n'*) : ;; # multi-line: fall through to the destructive checks
*)
if printf '%s' "$CMD" | grep -qE '^[[:space:]]*rm[[:space:]]+(-[a-zA-Z]*[rR][a-zA-Z]*[[:space:]]+|--recursive[[:space:]]+)(([^[:space:];&|#(`]*/)?(node_modules|\.next|dist|__pycache__|\.cache|build|\.turbo|coverage)[[:space:]]*)+$' 2>/dev/null; then
echo '{}'
exit 0
fi
;;
esac
# --- Destructive pattern checks ---
WARN=""