Fix challenge validation panic when follow-up hits ALLOW (#1278)

* fix(localization): correct formatting of Swedish loading message

* fix(main): correct formatting and improve readability in main.go

* fix(challenge): add difficulty and policy rule hash to challenge metadata

* docs(challenge): fix panic when validating challenges in privacy-mode browsers

cmd/anubis/main.go

@@ -145,7 +145,7 @@ func parseBindNetFromAddr(address string) (string, string) {
 	return "", address
 }
 
-func parseSameSite(s string) (http.SameSite) {
+func parseSameSite(s string) http.SameSite {
 	switch strings.ToLower(s) {
 	case "none":
 		return http.SameSiteNoneMode

docs/docs/CHANGELOG.md

@@ -13,6 +13,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 <!-- This changes the project to: -->
 
+- Fix panic when validating challenges after privacy-mode browsers strip headers and the follow-up request matches an `ALLOW` threshold.
 - Expose WEIGHT rule matches as Prometheus metrics.
 - Allow more OCI registry clients [based on feedback](https://github.com/TecharoHQ/anubis/pull/1253#issuecomment-3506744184).
 - Expose services directory in the embedded `(data)` filesystem.

lib/anubis.go

@@ -121,6 +121,8 @@ func (s *Server) issueChallenge(ctx context.Context, r *http.Request, lg *slog.L
 		Method:         rule.Challenge.Algorithm,
 		RandomData:     fmt.Sprintf("%x", randomData),
 		IssuedAt:       time.Now(),
+		Difficulty:     rule.Challenge.Difficulty,
+		PolicyRuleHash: rule.Hash(),
 		Metadata: map[string]string{
 			"User-Agent": r.Header.Get("User-Agent"),
 			"X-Real-Ip":  r.Header.Get("X-Real-Ip"),
@@ -137,6 +139,44 @@ func (s *Server) issueChallenge(ctx context.Context, r *http.Request, lg *slog.L
 	return &chall, err
 }
 
+func (s *Server) hydrateChallengeRule(rule *policy.Bot, chall *challenge.Challenge, lg *slog.Logger) *policy.Bot {
+	if chall == nil {
+		return rule
+	}
+
+	if rule == nil {
+		rule = &policy.Bot{
+			Rules: &checker.List{},
+		}
+	}
+
+	if chall.Difficulty == 0 {
+		// fall back to whatever the policy currently says or the global default
+		if rule.Challenge != nil && rule.Challenge.Difficulty != 0 {
+			chall.Difficulty = rule.Challenge.Difficulty
+		} else {
+			chall.Difficulty = s.policy.DefaultDifficulty
+		}
+	}
+
+	if rule.Challenge == nil {
+		lg.Warn("rule missing challenge configuration; using stored challenge metadata", "rule", rule.Name)
+		rule.Challenge = &config.ChallengeRules{}
+	}
+
+	if rule.Challenge.Difficulty == 0 {
+		rule.Challenge.Difficulty = chall.Difficulty
+	}
+	if rule.Challenge.ReportAs == 0 {
+		rule.Challenge.ReportAs = chall.Difficulty
+	}
+	if rule.Challenge.Algorithm == "" {
+		rule.Challenge.Algorithm = chall.Method
+	}
+
+	return rule
+}
+
 func (s *Server) maybeReverseProxyHttpStatusOnly(w http.ResponseWriter, r *http.Request) {
 	s.maybeReverseProxy(w, r, true)
 }
@@ -461,6 +501,8 @@ func (s *Server) PassChallenge(w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	rule = s.hydrateChallengeRule(rule, chall, lg)
+
 	impl, ok := challenge.Get(chall.Method)
 	if !ok {
 		lg.Error("check failed", "err", err)

lib/anubis_test.go

@@ -2,6 +2,7 @@ package lib
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -18,8 +19,10 @@ import (
 	"github.com/TecharoHQ/anubis"
 	"github.com/TecharoHQ/anubis/data"
 	"github.com/TecharoHQ/anubis/internal"
+	"github.com/TecharoHQ/anubis/lib/challenge"
 	"github.com/TecharoHQ/anubis/lib/policy"
 	"github.com/TecharoHQ/anubis/lib/policy/config"
+	"github.com/TecharoHQ/anubis/lib/store"
 	"github.com/TecharoHQ/anubis/lib/thoth/thothmock"
 )
 
@@ -1027,6 +1030,59 @@ func TestPassChallengeXSS(t *testing.T) {
 	})
 }
 
+func TestPassChallengeNilRuleChallengeFallback(t *testing.T) {
+	pol := loadPolicies(t, "testdata/zero_difficulty.yaml", 0)
+
+	srv := spawnAnubis(t, Options{
+		Next:   http.NewServeMux(),
+		Policy: pol,
+	})
+
+	allowThreshold, err := policy.ParsedThresholdFromConfig(config.Threshold{
+		Name: "allow-all",
+		Expression: &config.ExpressionOrList{
+			Expression: "true",
+		},
+		Action: config.RuleAllow,
+	})
+	if err != nil {
+		t.Fatalf("can't compile test threshold: %v", err)
+	}
+	srv.policy.Thresholds = []*policy.Threshold{allowThreshold}
+	srv.policy.Bots = nil
+
+	chall := challenge.Challenge{
+		ID:         "test-challenge",
+		Method:     "metarefresh",
+		RandomData: "apple cider",
+		IssuedAt:   time.Now().Add(-5 * time.Second),
+		Difficulty: 1,
+	}
+
+	j := store.JSON[challenge.Challenge]{Underlying: srv.store}
+	if err := j.Set(context.Background(), "challenge:"+chall.ID, chall, time.Minute); err != nil {
+		t.Fatalf("can't insert challenge into store: %v", err)
+	}
+
+	req := httptest.NewRequest(http.MethodGet, "https://example.com"+anubis.APIPrefix+"pass-challenge", nil)
+	q := req.URL.Query()
+	q.Set("redir", "/")
+	q.Set("id", chall.ID)
+	q.Set("challenge", chall.RandomData)
+	req.URL.RawQuery = q.Encode()
+	req.Header.Set("X-Real-Ip", "203.0.113.4")
+	req.Header.Set("User-Agent", "NilChallengeTester/1.0")
+	req.AddCookie(&http.Cookie{Name: anubis.TestCookieName, Value: chall.ID})
+
+	rr := httptest.NewRecorder()
+
+	srv.PassChallenge(rr, req)
+
+	if rr.Code != http.StatusFound {
+		t.Fatalf("expected redirect when validating challenge, got %d", rr.Code)
+	}
+}
+
 func TestXForwardedForNoDoubleComma(t *testing.T) {
 	var h http.Handler = http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("X-Forwarded-For", r.Header.Get("X-Forwarded-For"))

lib/challenge/challenge.go

@@ -10,4 +10,6 @@ type Challenge struct {
 	IssuedAt       time.Time         `json:"issuedAt"`                 // When the challenge was issued
 	Metadata       map[string]string `json:"metadata"`                 // Challenge metadata such as IP address and user agent
 	Spent          bool              `json:"spent"`                    // Has the challenge already been solved?
+	Difficulty     int               `json:"difficulty,omitempty"`     // Difficulty that was in effect when issued
+	PolicyRuleHash string            `json:"policyRuleHash,omitempty"` // Hash of the policy rule that issued this challenge
 }

lib/challenge/challengetest/challengetest.go

@@ -4,6 +4,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/TecharoHQ/anubis"
 	"github.com/TecharoHQ/anubis/internal"
 	"github.com/TecharoHQ/anubis/lib/challenge"
 	"github.com/google/uuid"
@@ -19,5 +20,6 @@ func New(t *testing.T) *challenge.Challenge {
 		ID:         id.String(),
 		RandomData: randomData,
 		IssuedAt:   time.Now(),
+		Difficulty: anubis.DefaultDifficulty,
 	}
 }