crowdsecurity/crowdsec · error

render challenge page: %w

Error message

render challenge page: %w

What it means

GetChallengePage renders the final challenge HTML via the runtime's htmlTpl template. If template execution fails (bad template syntax, missing/invalid template data fields), the error is wrapped as 'render challenge page'. This is an internal template/data contract failure, not a client problem.

Source

Thrown at pkg/appsec/challenge/challenge.go:600

	// carries the per-epoch K, so K never appears in plain HTML.
	dynamicModule, err := c.currentDynamicModule(ctx)
	if err != nil {
		return "", fmt.Errorf("build dynamic key module: %w", err)
	}

	var renderedPage strings.Builder

	if err := c.htmlTpl.Execute(&renderedPage, map[string]interface{}{
		"JSChallenge":   challengeCode,
		"DynamicModule": dynamicModule,
		"FPScannerPath": ChallengeFPScannerPath,
		"PowDifficulty": difficulty,
		"PowPrefix":     powSalt,
		"PowMAC":        powMAC,
		"Timestamp":     ts,
		"R":             r,
	}); err != nil {
		return "", fmt.Errorf("render challenge page: %w", err)
	}
	return renderedPage.String(), nil
}

// ValidateChallengeResponse parses a submit POST and runs the full chain:
// freshness + PoW-salt authenticity + difficulty, PoW solution,
// the submission signature `sig` (keyed by the never-transmitted s = HMAC(K_epoch, r)),
// a single-use burn of `r` (replay protection),
// and fingerprint de-obfuscation. On success it returns the sealed
// cookie, decoded FingerprintData, and the proven PoW difficulty; failures
// return a generic error so the caller doesn't leak which stage failed.
func (c *ChallengeRuntime) ValidateChallengeResponse(request *http.Request, body []byte) (*cookie.AppsecCookie, FingerprintData, int, error) {
	vars, err := url.ParseQuery(string(body))
	if err != nil {
		return nil, FingerprintData{}, 0, fmt.Errorf("%w: %w", ErrChallengePayload, err)
	}

	encryptedFingerprint := vars.Get("f")

View on GitHub (pinned to 909b515798)

Solutions

1. Rebuild from a clean tree so the embedded htmlTpl matches the data the code passes (`make build`).
2. Check the wrapped error for the template name/line it reports and fix that template spot.
3. If you customized the template, re-sync it with the data keys rendered by GetChallengePage.
4. Report upstream if it reproduces on an unmodified build — it indicates a code/template contract bug.

page, err := rt.GetChallengePage(ctx, opts)
if err != nil {
    if strings.Contains(err.Error(), "render challenge page") {
        logger.WithError(err).Error("challenge template render failed; check embedded template/data contract")
        http.Error(w, "internal error", http.StatusInternalServerError)
    }
}

When it happens

Trigger: Calling GetChallengePage when htmlTpl.Execute returns an error — malformed embedded template, or template data map missing a field the template references (JSChallenge, DynamicModule, PowDifficulty, PowPrefix, PowMAC, Timestamp, R).

Common situations: Custom/patched builds with edited challenge HTML templates; a build where the embedded template drifted from the data map keys; extremely rare runtime write failures.

Related errors

• ErrChallengeFields
• ErrChallengeTicket
• unable to get challenge page: %w
• unable to seal allowlist cookie: %w
• failed to generate initial challenge bundle: %w

AI-assisted analysis of crowdsecurity/crowdsec@909b515798 (2026-09-06). Data as JSON: /api/errors/9204e55eaf9cb618. Report an issue: GitHub.