fix(hooks): close the five escapes the skills#52 review found
- Fail-closed path no longer needs jq: the ask JSON is a printf literal, and a host without jq asks instead of staying silent. - A tool_name that is not a non-empty string asks (was: no opinion). - Gate workflow_run_trigger, tag_create, release_create, and file_write_branch when it lands on main/master, has no branch, or empties a file (same effect as pr_merge / file_delete). - Header claim narrowed: gitea-mcp spellings on any server name, not other servers' spellings of the same operation. - Tests run the hook as hooks.json does (bash <path>), assert exit 0 on every case, and cover null/missing/wrong-type tool_name, last-segment verb parsing and a PATH without jq. 13 new cases were red first. Refs mathias/infra#508 Bump-Type: minor Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
This commit is contained in:
Claude Opus 5.5
@@ -6,41 +6,67 @@
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# so an agent holds the full scope of the caller's PAT. repo_delete's own guard
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# (confirm == repo) is filled in by the model on both sides: it stops typos,
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# not an injected or mistaken agent. The infra-mcp README claimed client-side
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# deny lists covered this; on 2026-10-01 none existed on any settings file.
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# deny lists covered this; on 2026-10-01 none existed in any settings file.
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#
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# Policy: match the VERB, not the server. The same tool is reachable as
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# mcp__plugin_skills_gitea__*, mcp__claude_ai_gitea__* (connector) or under
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# any name a host registers it with, so keying on the server name would let a
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# rename bypass the gate.
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# Policy: match gitea-mcp's verb spellings on ANY server name. The same tool is
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# reachable as mcp__plugin_skills_gitea__*, mcp__claude_ai_gitea__* or under
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# whatever name a host registers it with, so keying on the server name would
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# let a rename bypass the gate. It does NOT recognise other servers' spellings
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# of the same operation (e.g. a third-party `delete_repo`).
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#
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# Emits "ask" or nothing. Never "allow": a hook allow would override the
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# user's own deny/ask rules. Malformed input fails closed (ask).
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# file_write_branch is gated when it would land on main/master (on infra that
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# is a Flux deploy within ~60s — the same effect as pr_merge) or empty a file
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# (the same effect as file_delete). Writes to other branches pass.
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#
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# Scope limit, recorded in the ADR: this gates MCP calls only. A session with
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# the PAT in its environment can still reach the Gitea REST API via Bash.
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# Emits "ask" or nothing; never "allow" (a hook allow would override the
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# user's own deny/ask rules). Always exits 0: Claude Code ignores a hook's
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# JSON on a non-zero exit. Anything it cannot parse — including a host
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# without jq — fails closed to "ask". The ask JSON is a literal, so the
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# fail-closed path needs no tool that might be missing.
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#
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# Scope limit, recorded in infra ADR-0027: this gates MCP calls only. A
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# session with the PAT in its environment can still reach the Gitea REST API
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# through a shell.
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set -uo pipefail
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set -u
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DESTRUCTIVE='repo_delete|file_delete|branch_delete|pr_merge|tbd_ship|repo_update|repo_mirror_push'
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DESTRUCTIVE='repo_delete|file_delete|branch_delete|pr_merge|tbd_ship|repo_update|repo_mirror_push|workflow_run_trigger|tag_create|release_create'
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ask() {
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jq -n --arg reason "$1" \
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'{hookSpecificOutput: {hookEventName: "PreToolUse", permissionDecision: "ask", permissionDecisionReason: $reason}}'
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# $1 must contain only [A-Za-z0-9 _.:()'/-] — it is spliced into JSON verbatim.
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printf '{"hookSpecificOutput":{"hookEventName":"PreToolUse","permissionDecision":"ask","permissionDecisionReason":"%s"}}\n' "$1"
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exit 0
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}
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INPUT="$(cat)"
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if ! TOOL_NAME="$(printf '%s' "$INPUT" | jq -er '.tool_name' 2>/dev/null)"; then
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ask "mcp-destructive-guard: could not parse the tool call, so it cannot be shown safe. Approve only if you expected it."
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command -v jq >/dev/null 2>&1 \
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|| ask "mcp-destructive-guard: jq is not installed, so this MCP call cannot be checked. Approve only if you expected it."
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if ! TOOL_NAME="$(printf '%s' "$INPUT" | jq -er '.tool_name | strings | select(length > 0)' 2>/dev/null)"; then
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ask "mcp-destructive-guard: could not read a tool name from this call, so it cannot be shown safe. Approve only if you expected it."
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fi
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verb="${TOOL_NAME##*__}"
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case "$TOOL_NAME" in
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mcp__*__*) ;;
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*) exit 0 ;;
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esac
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verb="${TOOL_NAME##*__}"
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safe_verb="$(printf '%s' "$verb" | tr -cd 'A-Za-z0-9_-')"
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if printf '%s' "$verb" | grep -Eqix "($DESTRUCTIVE)"; then
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ask "Irreversible MCP verb '$verb' (infra ADR-0027): needs your approval. The model filled in every argument, including any confirm field."
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ask "Irreversible MCP verb '$safe_verb' (infra ADR-0027): needs your approval. The model filled in every argument, including any confirm field."
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fi
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if printf '%s' "$verb" | grep -Eqix 'file_write_branch'; then
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verdict="$(printf '%s' "$INPUT" | jq -r '
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.tool_input as $i
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| if ($i | type) != "object" then "ask"
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elif (($i.branch // "") | ascii_downcase) as $b | ($b == "" or $b == "main" or $b == "master") then "ask"
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elif (($i.content // "") == "") then "ask"
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else "pass" end' 2>/dev/null || echo ask)"
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[ "$verdict" = "pass" ] \
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|| ask "file_write_branch to main/master, with no branch, or emptying a file (infra ADR-0027): needs your approval."
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fi
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exit 0
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@@ -4,9 +4,11 @@
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#
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# Contract: reads PreToolUse hook JSON on stdin, ALWAYS exits 0, and answers
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# in hookSpecificOutput.permissionDecision. "ask" = a human must approve;
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# no decision emitted ("NONE") = the guard stays out of the way and normal
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# permission rules apply. The guard never emits "allow": an allow from a hook
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# would bypass the user's own deny/ask rules.
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# empty stdout ("NONE") = no opinion, normal permission rules apply. The guard
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# never emits "allow": an allow from a hook would bypass the user's own rules.
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#
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# Cases marked (gatekeeper) are escapes found by the skills#52 review: each
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# passed the first version of this suite.
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set -u
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@@ -16,60 +18,82 @@ GUARD="$ROOT/hooks/mcp-destructive-guard.sh"
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pass=0
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fail=0
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# An empty stdout is a valid hook answer ("no opinion"), reported as NONE.
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decode() {
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_out=$(cat)
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[ -z "$_out" ] && { echo NONE; return; }
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printf '%s' "$_out" | jq -r '.hookSpecificOutput.permissionDecision // "NONE"' 2>/dev/null || echo BROKEN
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# run_guard <json> [PATH] — invoked exactly as hooks.json does: `bash <path>`.
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# Prints "<decision> rc=<exit>", decision NONE for an empty answer.
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run_guard() {
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if [ $# -ge 2 ]; then
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_out=$(printf '%s' "$1" | PATH="$2" "$BASH_BIN" "$GUARD"); _rc=$?
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else
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_out=$(printf '%s' "$1" | bash "$GUARD"); _rc=$?
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fi
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if [ -z "$_out" ]; then _d=NONE
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else _d=$(printf '%s' "$_out" | jq -r '.hookSpecificOutput.permissionDecision // "NONE"' 2>/dev/null || echo BROKEN)
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fi
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printf '%s rc=%s' "$_d" "$_rc"
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}
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BASH_BIN=$(command -v bash)
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decision_for() {
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jq -n --arg t "$1" '{tool_name: $t, tool_input: {owner: "mathias", repo: "x"}}' \
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| "$GUARD" | decode
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}
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expect() {
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_want=$1 _tool=$2 _label=$3
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_got=$(decision_for "$_tool")
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if [ "$_got" = "$_want" ]; then
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check() {
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_want=$1 _json=$2 _label=$3
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_got=$(run_guard "$_json")
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if [ "$_got" = "$_want rc=0" ]; then
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pass=$((pass + 1)); printf ' ok %s\n' "$_label"
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else
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fail=$((fail + 1)); printf ' FAIL %s\n want=%s got=%s tool=%s\n' "$_label" "$_want" "$_got" "$_tool"
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fail=$((fail + 1)); printf ' FAIL %s\n want=%s rc=0 got=%s\n in=%s\n' "$_label" "$_want" "$_got" "$_json"
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fi
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}
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tool() { printf '{"tool_name":"%s","tool_input":{"owner":"mathias","repo":"x"}}' "$1"; }
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echo "mcp-destructive-guard tests"
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# Irreversible verbs, on the plugin namespace.
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for v in repo_delete file_delete branch_delete pr_merge tbd_ship repo_update repo_mirror_push; do
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expect ask "mcp__plugin_skills_gitea__$v" "plugin gitea $v asks"
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for v in repo_delete file_delete branch_delete pr_merge tbd_ship repo_update repo_mirror_push \
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workflow_run_trigger tag_create release_create; do
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check ask "$(tool "mcp__plugin_skills_gitea__$v")" "plugin gitea $v asks"
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done
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# The same verb reached through a different server name must not slip past:
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# the claude.ai connector, a bare local registration, or any future rename.
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expect ask "mcp__claude_ai_gitea__repo_delete" "connector namespace asks"
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expect ask "mcp__gitea__repo_delete" "bare server name asks"
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expect ask "mcp__git__repo_delete" "renamed server still asks"
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# The verb is matched on any server name: connector, bare, or renamed.
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check ask "$(tool mcp__claude_ai_gitea__repo_delete)" "connector namespace asks"
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check ask "$(tool mcp__gitea__repo_delete)" "bare server name asks"
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check ask "$(tool mcp__git__repo_delete)" "renamed server still asks"
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check ask "$(tool mcp__plugin_skills_gitea__REPO_DELETE)" "uppercase verb asks"
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# The verb is the LAST segment (gatekeeper: parsing the second segment stayed green).
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check ask "$(tool mcp__a__b__repo_delete)" "verb taken from last segment"
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check NONE "$(tool mcp__repo_delete__issue_get)" "server named like a verb does not trigger"
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# Case variants must not bypass (tool names are matched exactly by the host,
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# but a guard that lowercases nothing should not depend on that).
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expect ask "mcp__plugin_skills_gitea__REPO_DELETE" "uppercase verb asks"
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# file_write_branch: content landing on main, or emptying a file, is the same
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# effect as the gated pr_merge / file_delete (gatekeeper).
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fwb() { printf '{"tool_name":"mcp__plugin_skills_gitea__file_write_branch","tool_input":{"branch":"%s","content":"%s"}}' "$1" "$2"; }
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check ask "$(fwb main x)" "file_write_branch to main asks"
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check ask "$(fwb master x)" "file_write_branch to master asks"
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check ask "$(fwb feat/y '')" "file_write_branch emptying a file asks"
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check ask '{"tool_name":"mcp__plugin_skills_gitea__file_write_branch","tool_input":{"content":"x"}}' "file_write_branch without branch asks"
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check NONE "$(fwb feat/y x)" "file_write_branch to a feature branch passes"
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# Reversible / read verbs pass through untouched.
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for v in issue_close issue_create file_read repo_list pr_create file_write_branch; do
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expect NONE "mcp__plugin_skills_gitea__$v" "$v passes through"
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# Reversible / read verbs pass through.
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for v in issue_close issue_create file_read repo_list pr_create; do
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check NONE "$(tool "mcp__plugin_skills_gitea__$v")" "$v passes through"
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done
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check NONE "$(tool mcp__plugin_skills_gitea__repo_delete_dry_run_list)" "suffix near-miss passes"
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check NONE "$(tool Bash)" "non-MCP tool passes"
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check NONE "$(tool repo_delete)" "non-MCP tool named like a verb passes"
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# Near-miss names are not the guarded verb.
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expect NONE "mcp__plugin_skills_gitea__repo_delete_dry_run_list" "suffix near-miss passes"
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expect NONE "Bash" "non-MCP tool passes"
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# Malformed input fails CLOSED (gatekeeper: non-string tool_name got NONE).
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check ask 'not json' "non-JSON asks"
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check ask '{}' "missing tool_name asks"
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check ask '{"tool_name":null}' "null tool_name asks"
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check ask '{"tool_name":""}' "empty tool_name asks"
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check ask '{"tool_name":5}' "number tool_name asks"
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check ask '{"tool_name":["mcp__x__repo_delete"]}' "array tool_name asks"
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check ask '{"tool_name":{"a":1}}' "object tool_name asks"
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# Malformed input fails CLOSED (ask), never open.
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_got=$(printf 'not json' | "$GUARD" | decode)
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if [ "$_got" = "ask" ]; then pass=$((pass+1)); echo " ok malformed input asks"; else fail=$((fail+1)); echo " FAIL malformed input: got=$_got"; fi
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# Executed as a program, like Claude Code does (shebang decides interpreter).
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[ -x "$GUARD" ] && { pass=$((pass+1)); echo " ok guard is executable"; } || { fail=$((fail+1)); echo " FAIL guard not executable"; }
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# Without jq on PATH the guard must still answer ask, not stay silent
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# (gatekeeper: the fail-closed path itself needed jq).
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nojq=$(mktemp -d); trap 'rm -rf "$nojq"' EXIT
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for b in bash cat grep tr sed; do ln -s "$(command -v $b)" "$nojq/$b"; done
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_got=$(run_guard "$(tool mcp__plugin_skills_gitea__repo_delete)" "$nojq")
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if [ "$_got" = "ask rc=0" ]; then pass=$((pass+1)); echo " ok no jq on PATH still asks"; else fail=$((fail+1)); echo " FAIL no jq on PATH: got=$_got"; fi
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_got=$(run_guard "$(tool mcp__plugin_skills_gitea__issue_get)" "$nojq")
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if [ "$_got" = "ask rc=0" ]; then pass=$((pass+1)); echo " ok no jq on PATH asks even for a read verb (cannot parse = cannot clear)"; else fail=$((fail+1)); echo " FAIL no jq read verb: got=$_got"; fi
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printf '\n%d passed, %d failed\n' "$pass" "$fail"
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[ "$fail" -eq 0 ]
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