Wire-format JSON tag consistency fix, and the first real plugin

Writing PLUGINS.md as an authoritative external spec surfaced a real,
pre-existing bug: store.Summary/Entry/EntryTag/WSMessage, rules.Rule,
scope.Rule, and clientcert.Cert had no JSON struct tags at all, so Go's
default marshaling serialized them PascalCase ("ID", "StartedAt")
while the rest of the protocol (EntryDetail's own fields, every
Request/Response wrapper field) uses snake_case. Confirmed live against
a real daemon before touching anything: a raw socket "list" request
came back with "ID"/"StartedAt"/"StatusCode", exactly the mismatch
suspected. Nothing outside this repo's own Go code consumes this wire
format yet, so this was a free, purely additive fix rather than
something to work around - every affected struct now tags snake_case
consistently.

plugins/authcheck is the first real plugin: an Autorize-style
authorization checker. For every proxied request carrying an
Authorization or Cookie header, resends it with that header stripped
and compares status classes - a resend that still succeeds where the
original did too is a likely missing-function-level-access-control
bug, tagged authcheck:bypass with structured detail. Deliberately
speaks the wire protocol directly (its own local request/response/
summary/entryDetail structs mirroring the real ones field-for-field,
not imported from internal/ipc) rather than taking the shortcut a Go
plugin could - proof the documented protocol is actually sufficient on
its own, since that's all a non-Go plugin author has to work with.

Verified live end to end: a real daemon, a real Python origin with one
endpoint that looks like it enforces auth but doesn't (vulnerable by
design) and one that actually does (the control case) - the broken
endpoint was correctly tagged, the secure one correctly left alone, no
false positive, confirmed both via the stored tag data directly and
visually in the TUI (tmux, real keystrokes): the Tags column badge, T's
tag list, and the tag detail view's JSON-colorized data (ANSI-verified,
not eyeballed) all showing the plugin's actual findings.

1 files changed, 265 insertions, 0 deletions

diff --git a/plugins/authcheck/main.go b/plugins/authcheck/main.go
new file mode 100644
index 0000000..8f2a5ec
--- /dev/null
+++ b/plugins/authcheck/main.go
@@ -0,0 +1,265 @@
+// Command authcheck is a reference mitmux plugin - an Autorize-style
+// authorization checker - and, deliberately, a template: it speaks
+// mitmux's plugin wire protocol directly (raw JSON over the control
+// socket, see PLUGINS.md) rather than importing mitmux's own internal
+// Go packages, the same way a plugin written in any other language
+// would have to. That's not a style preference - it's what actually
+// proves PLUGINS.md's documented protocol is sufficient on its own,
+// rather than silently depending on Go-internal conveniences a
+// non-Go plugin author wouldn't have access to.
+//
+// What it does: for every captured request that carries an
+// Authorization or Cookie header, resends the exact same request with
+// that header stripped and compares the result. A resend that still
+// succeeds where the original also succeeded means the endpoint
+// doesn't actually enforce the authentication it appears to require -
+// a missing-function-level-access-control bug, one of the more common
+// real findings this class of check turns up. Matches are tagged
+// "authcheck:bypass" on the original entry, with structured detail (the
+// original status vs. the anonymous resend's) for the TUI's tag panel.
+//
+// This is the simplified half of what Burp's Autorize does: Autorize
+// additionally supports swapping in a SECOND, lower-privileged
+// identity's session and comparing against that - useful for catching
+// cross-account IDORs a fully-anonymous check can't see. That needs a
+// second credential as input, which this reference version doesn't
+// take; a -low-priv-cookie flag doing that is a natural, small
+// extension of the same pattern used here.
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"log"
+	"net"
+	"net/http"
+	"os"
+	"path/filepath"
+)
+
+// request/response mirror internal/ipc's wire structs field-for-field
+// (see PLUGINS.md) - defined fresh here, not imported, so this file
+// only ever exercises what's actually documented as the public
+// protocol.
+type request struct {
+	Type      string `json:"type"`
+	ID        int64  `json:"id,omitempty"`
+	Scheme    string `json:"scheme,omitempty"`
+	Host      string `json:"host,omitempty"`
+	Raw       []byte `json:"raw,omitempty"`
+	TagPlugin string `json:"tag_plugin,omitempty"`
+	Tag       string `json:"tag,omitempty"`
+	TagData   string `json:"tag_data,omitempty"`
+}
+
+type summary struct {
+	ID     int64  `json:"id"`
+	Method string `json:"method"`
+	Scheme string `json:"scheme"`
+	Host   string `json:"host"`
+	Path   string `json:"path"`
+	Source string `json:"source"`
+}
+
+type entryDetail struct {
+	summary
+	StatusCode int    `json:"status_code"`
+	RequestRaw []byte `json:"request_raw"`
+}
+
+type response struct {
+	Type    string       `json:"type"`
+	Entries []summary    `json:"entries,omitempty"`
+	New     *summary     `json:"new,omitempty"`
+	Detail  *entryDetail `json:"detail,omitempty"`
+	TagID   int64        `json:"tag_id,omitempty"`
+	Error   string       `json:"error,omitempty"`
+}
+
+// client is a minimal request/response connection - send one request,
+// read back one response, repeat. A plugin also needs a second,
+// separate connection for "subscribe" (see main): that one is only
+// ever written to once and then just read from continuously, so it
+// doesn't need this type's request/response pairing at all.
+type client struct {
+	conn net.Conn
+	enc  *json.Encoder
+	dec  *json.Decoder
+}
+
+func dial(path string) (*client, error) {
+	conn, err := net.Dial("unix", path)
+	if err != nil {
+		return nil, err
+	}
+	return &client{conn: conn, enc: json.NewEncoder(conn), dec: json.NewDecoder(conn)}, nil
+}
+
+func (c *client) call(req request) (response, error) {
+	if err := c.enc.Encode(req); err != nil {
+		return response{}, err
+	}
+	var resp response
+	if err := c.dec.Decode(&resp); err != nil {
+		return response{}, err
+	}
+	if resp.Type == "error" {
+		return response{}, fmt.Errorf("%s", resp.Error)
+	}
+	return resp, nil
+}
+
+func defaultSocketPath() string {
+	if rt := os.Getenv("XDG_RUNTIME_DIR"); rt != "" {
+		return filepath.Join(rt, "mitmux.sock")
+	}
+	// Matches internal/ca.Dir() without importing it - see this file's
+	// package doc for why plugins shouldn't reach into mitmux's own Go
+	// internals even when it would be more convenient.
+	cfg, err := os.UserConfigDir()
+	if err != nil {
+		return "mitmux.sock"
+	}
+	return filepath.Join(cfg, "mitmux", "mitmux.sock")
+}
+
+// authHeaders are checked in order; the first one present on a request
+// is what gets stripped for the anonymous resend. Checking more than
+// one matters: an API might authenticate via a bearer token while a
+// browser-driven flow on the same host uses a session cookie, and both
+// are worth checking independently rather than only ever picking one.
+var authHeaders = []string{"Authorization", "Cookie"}
+
+type result struct {
+	OriginalStatus int    `json:"original_status"`
+	ResendStatus   int    `json:"resend_status"`
+	StrippedHeader string `json:"stripped_header"`
+	Verdict        string `json:"verdict"`
+}
+
+func main() {
+	socketPath := flag.String("socket", "", "daemon control socket path (default: same as mitmux itself)")
+	pluginName := flag.String("name", "authcheck", "name this plugin tags entries as")
+	flag.Parse()
+
+	path := *socketPath
+	if path == "" {
+		path = defaultSocketPath()
+	}
+
+	actor, err := dial(path)
+	if err != nil {
+		log.Fatalf("dial %s: %v", path, err)
+	}
+	defer actor.conn.Close()
+
+	subConn, err := net.Dial("unix", path)
+	if err != nil {
+		log.Fatalf("dial %s (subscribe): %v", path, err)
+	}
+	defer subConn.Close()
+	if err := json.NewEncoder(subConn).Encode(request{Type: "subscribe"}); err != nil {
+		log.Fatalf("subscribe: %v", err)
+	}
+
+	log.Printf("authcheck: watching live traffic on %s", path)
+	dec := json.NewDecoder(subConn)
+	for {
+		var resp response
+		if err := dec.Decode(&resp); err != nil {
+			log.Fatalf("subscribe feed closed: %v", err)
+		}
+		if resp.Type != "new" || resp.New == nil {
+			continue
+		}
+		sum := *resp.New
+		// Never touch our own resends - the daemon records a Repeat()
+		// as source="repeater", and reprocessing it would misfile the
+		// very control-group requests this check depends on (it also
+		// wouldn't loop: a resend already has its auth header removed,
+		// so it would never match authHeaders again - but it's still
+		// pointless work and pointless noise to try).
+		if sum.Source != "proxy" {
+			continue
+		}
+		if err := checkEntry(actor, *pluginName, sum.ID); err != nil {
+			log.Printf("entry #%d: %v", sum.ID, err)
+		}
+	}
+}
+
+func checkEntry(c *client, pluginName string, id int64) error {
+	resp, err := c.call(request{Type: "get", ID: id})
+	if err != nil {
+		return fmt.Errorf("get: %w", err)
+	}
+	if resp.Detail == nil {
+		return fmt.Errorf("get: no detail in response")
+	}
+	detail := *resp.Detail
+
+	req, err := http.ReadRequest(bufio.NewReader(bytes.NewReader(detail.RequestRaw)))
+	if err != nil {
+		return nil // not a well-formed request we can safely reparse - skip, not fatal
+	}
+
+	var strippedHeader string
+	for _, h := range authHeaders {
+		if req.Header.Get(h) != "" {
+			strippedHeader = h
+			break
+		}
+	}
+	if strippedHeader == "" {
+		return nil // nothing to check
+	}
+
+	req2, err := http.ReadRequest(bufio.NewReader(bytes.NewReader(detail.RequestRaw)))
+	if err != nil {
+		return nil
+	}
+	req2.Header.Del(strippedHeader)
+
+	var buf bytes.Buffer
+	if err := req2.Write(&buf); err != nil {
+		return fmt.Errorf("rebuild request: %w", err)
+	}
+
+	repeatResp, err := c.call(request{Type: "repeat", Scheme: detail.Scheme, Host: detail.Host, Raw: buf.Bytes()})
+	if err != nil {
+		return fmt.Errorf("repeat: %w", err)
+	}
+	if repeatResp.Detail == nil {
+		return fmt.Errorf("repeat: no detail in response")
+	}
+	resentStatus := repeatResp.Detail.StatusCode
+
+	suspicious := successClass(detail.StatusCode) && successClass(resentStatus)
+	if !suspicious {
+		return nil // matches Burp's own default: only surface likely findings, not every check performed
+	}
+
+	data, err := json.Marshal(result{
+		OriginalStatus: detail.StatusCode,
+		ResendStatus:   resentStatus,
+		StrippedHeader: strippedHeader,
+		Verdict:        "bypass",
+	})
+	if err != nil {
+		return fmt.Errorf("marshal result: %w", err)
+	}
+
+	if _, err := c.call(request{Type: "tag_entry", ID: id, TagPlugin: pluginName, Tag: "authcheck:bypass", TagData: string(data)}); err != nil {
+		return fmt.Errorf("tag_entry: %w", err)
+	}
+	log.Printf("#%d %s %s -> possible auth bypass: %d without %s still got %d",
+		id, detail.Method, detail.Path, detail.StatusCode, strippedHeader, resentStatus)
+	return nil
+}
+
+func successClass(status int) bool {
+	return status >= 200 && status < 400
+}