fix: prevent reflected XSS in WebSub intent verification (Instagram & Facebook) by AnkitPorwal04 · Pull Request #8662 · erxes/erxes

AnkitPorwal04 · Jul 9, 2026

Summary

Fixes a reflected XSS vulnerability in the WebSub (PubSub) intent verification handlers for both Instagram and Facebook integrations.

Problem

The instagramSubscription and facebookSubscription handlers echo back the hub.challenge query parameter via res.send() without setting an explicit Content-Type. Express defaults to text/html for string responses, which means a crafted hub.challenge value containing <script> tags or other HTML will be rendered by the browser — a classic reflected XSS.

Affected files:

backend/plugins/frontline_api/src/modules/integrations/instagram/controller/controller.ts
backend/plugins/frontline_api/src/modules/integrations/facebook/controller/controller.ts

Fix

Set Content-Type: text/plain before sending the response using res.type('text/plain').send(...). This ensures the browser treats the reflected value as plain text, not HTML. This is also consistent with the W3C WebSub specification which expects the challenge to be echoed as-is without HTML interpretation.

Changes

res.send(req.query['hub.challenge']) → res.type('text/plain').send(req.query['hub.challenge'])

Applied to both Instagram and Facebook subscription handlers.

Fixes #7855

Summary by Sourcery

Set WebSub intent verification responses for Instagram and Facebook to return the hub.challenge as plain text to mitigate reflected XSS.

Bug Fixes:

Prevent reflected XSS in Instagram WebSub subscription verification by sending the hub.challenge with a text/plain content type.
Prevent reflected XSS in Facebook WebSub subscription verification by sending the hub.challenge with a text/plain content type.

Summary by CodeRabbit

Bug Fixes
- Improved webhook verification responses for the Facebook and Instagram integrations by returning the verification challenge as plain text.
- Ensures the hub.challenge value is sent consistently in the expected response format, improving compatibility with third-party verification callbacks.

… Facebook) Set Content-Type to text/plain when echoing hub.challenge in the WebSub subscription verification handlers. Express defaults to text/html for string responses, allowing a crafted hub.challenge parameter to inject arbitrary HTML/JS. Fixes erxes#7855

sourcery-ai · Jul 9, 2026

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR hardens the WebSub intent verification endpoints for Instagram and Facebook by explicitly setting the response Content-Type to text/plain when echoing the hub.challenge value, preventing reflected XSS while staying compliant with the WebSub spec.

Sequence diagram for WebSub intent verification with safe hub.challenge echo

sequenceDiagram
    actor Client
    participant WebSubEndpoint

    Client->>WebSubEndpoint: GET /subscription?hub.mode=subscribe&hub.verify_token&hub.challenge
    alt hub.verify_token valid
        WebSubEndpoint->>Client: res.type('text/plain').send(hub.challenge)
    else hub.verify_token invalid
        WebSubEndpoint->>Client: res.send('OK')
    end

File-Level Changes

Change	Details	Files
Force plain-text responses when echoing WebSub hub.challenge in subscription handlers to prevent reflected XSS.	Update Instagram subscription handler to send hub.challenge with Content-Type text/plain instead of default text/html Update Facebook subscription handler to send hub.challenge with Content-Type text/plain instead of default text/html	`backend/plugins/frontline_api/src/modules/integrations/instagram/controller/controller.ts` `backend/plugins/frontline_api/src/modules/integrations/facebook/controller/controller.ts`

Assessment against linked issues

Issue	Objective	Addressed	Explanation
#7855	Prevent reflected XSS in the Instagram WebSub intent verification by ensuring the echoed `hub.challenge` value is not served with an HTML content type.	✅
#7855	Apply the same WebSub intent verification XSS mitigation to the Facebook integration’s `facebookSubscription` handler, ensuring `hub.challenge` is returned as plain text.	✅

Possibly linked issues

Potential reflected XSS in the WebSub intent verification #7855: PR mitigates the reported WebSub reflected XSS by sending hub.challenge as text/plain for Instagram and Facebook.

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coderabbitai · Jul 9, 2026

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: defaults

Review profile: CHILL

Plan: Pro

Run ID: b4e0315a-c2a3-48b3-9e70-992290ea249c

📥 Commits

Reviewing files that changed from the base of the PR and between 6d6ede5 and 8cc1e51.

📒 Files selected for processing (2)

backend/plugins/frontline_api/src/modules/integrations/facebook/controller/controller.ts
backend/plugins/frontline_api/src/modules/integrations/instagram/controller/controller.ts

✅ Files skipped from review due to trivial changes (1)

backend/plugins/frontline_api/src/modules/integrations/facebook/controller/controller.ts

🚧 Files skipped from review as they are similar to previous changes (1)

backend/plugins/frontline_api/src/modules/integrations/instagram/controller/controller.ts

📝 Walkthrough

Walkthrough

The Facebook and Instagram webhook verification handlers now set Content-Type: text/plain before returning the hub.challenge value or the fallback OK response.

Changes

Webhook Verification Response Type

Layer / File(s)	Summary
Set text/plain content type on challenge response `backend/plugins/frontline_api/src/modules/integrations/facebook/controller/controller.ts`, `backend/plugins/frontline_api/src/modules/integrations/instagram/controller/controller.ts`	Both webhook subscription handlers now set `res.type('text/plain')` before sending the verification challenge or fallback `OK` response, and the challenge value is explicitly converted to a string.

Estimated code review effort: 1 (Trivial) | ~2 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly summarizes the main fix: preventing reflected XSS in WebSub intent verification for Instagram and Facebook.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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sourcery-ai

Hey - I've left some high level feedback:

Consider explicitly casting req.query['hub.challenge'] to a string before sending (e.g. String(...)) to avoid unexpected behavior if the query value is an array or other non-string type.
For consistency and to avoid any future ambiguity, you may also want to set text/plain on the non-challenge responses in these handlers (e.g. the 'OK' path) so all subscription verification responses use a predictable content type.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider explicitly casting `req.query['hub.challenge']` to a string before sending (e.g. `String(...)`) to avoid unexpected behavior if the query value is an array or other non-string type.
- For consistency and to avoid any future ambiguity, you may also want to set `text/plain` on the non-challenge responses in these handlers (e.g. the `'OK'` path) so all subscription verification responses use a predictable content type.

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- Cast hub.challenge to String() to handle array query params safely - Set Content-Type text/plain on all subscription verification responses for consistency (including the 'OK' fallback path)

sonarqubecloud · Jul 9, 2026

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
0.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

sourcery-ai Bot reviewed Jul 9, 2026

View reviewed changes

refactor: address Sourcery review feedback

8cc1e51

- Cast hub.challenge to String() to handle array query params safely - Set Content-Type text/plain on all subscription verification responses for consistency (including the 'OK' fallback path)

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fix: prevent reflected XSS in WebSub intent verification (Instagram & Facebook) - #8662

fix: prevent reflected XSS in WebSub intent verification (Instagram & Facebook)#8662
AnkitPorwal04 wants to merge 2 commits into
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AnkitPorwal04:fix/websub-reflected-xssAnkitPorwal04/erxes:fix/websub-reflected-xssCopy head branch name to clipboard

AnkitPorwal04 commented Jul 9, 2026 •

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sourcery-ai Bot commented Jul 9, 2026 •

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Reviewer's Guide

Sequence diagram for WebSub intent verification with safe hub.challenge echo

File-Level Changes

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Summary

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Reviewer's Guide

Sequence diagram for WebSub intent verification with safe hub.challenge echo

File-Level Changes

Assessment against linked issues

Possibly linked issues

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sonarqubecloud Bot commented Jul 9, 2026

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AnkitPorwal04 commented Jul 9, 2026 •

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