---
id: "CVE-2026-87901"
kind: "vulnerability"
aliases: ["CVE-2026-87901"]
title: "Registration module lets reflected script injection run in victims' browsers"
severity: "high"
cvss: 8.3
epss: 0.00393
exploited: false
status: "open"
category: "other"
products: [{"name": "phpBB", "fixed": ["3.3.19"], "affected": ">= 3.3.0, <= 3.3.18", "ecosystem": "vendor"}]
ecosystems: ["vendor"]
tags: ["forum", "other", "php", "phpbb", "self-hosted", "web-app", "xss"]
not_affected_if: ["phpbb-3.3.19"]
published_at: "2026-10-23T17:17:22+00:00"
first_seen_at: "2026-10-23T21:57:34+00:00"
updated_at: "2026-10-25T12:38:49+00:00"
sources: [{"source": "nvd", "url": "https://nvd.nist.gov/vuln/detail/CVE-2026-87901", "first_seen_at": "2026-10-23T21:57:34+00:00"}, {"source": "analyst", "url": null, "first_seen_at": "2026-10-25T03:15:11+00:00"}, {"source": "epss", "url": "https://api.first.org/data/v1/epss?cve=CVE-2026-87901", "first_seen_at": "2026-10-25T12:38:49+00:00"}]
---

# Registration module lets reflected script injection run in victims' browsers

The registration module does not sanitize input, so a crafted link can make it reflect script back to the visitor. An attacker who gets a victim to open that link can run script in the victim's browser session.

_Summary, check and fix written by a model from the sources; labelled as such._

## Affected

- vendor:phpBB affected >= 3.3.0, <= 3.3.18 fixed 3.3.19

## How to check

Check your phpBB version in the Admin Control Panel (ACP index shows the installed version) or in includes/constants.php (PHPBB_VERSION). Any 3.3.0 through 3.3.18 is exposed; 3.3.19 is fixed.

## Fix

Update phpBB to 3.3.19 (released 2026-09-24). 3.3.18 packages did not contain the fix; do not stop at 3.3.18.

## Timeline

- 2026-10-23T21:57:34+00:00 nvd https://nvd.nist.gov/vuln/detail/CVE-2026-87901
- 2026-10-25T03:15:11+00:00 analyst — Product is phpBB (NVD affected data + phpBB 3.3.18/3.3.19 announcements, SECURITY-301). 3.3.18 shipped without the fixes (packaging error), so 3.3.19 is the real fix. No exploitation or PoC found.
- 2026-10-25T12:38:49+00:00 epss https://api.first.org/data/v1/epss?cve=CVE-2026-87901

## Documents

- [advisory] phpBB 3.3.18 Release - Urgent update https://www.phpbb.com/community/viewtopic.php?t=2675239
- [fix] phpBB 3.3.19 Release - Urgent update https://www.phpbb.com/community/viewtopic.php?t=2675305

## From the sources

Improper sanitization in the registration module allows reflected Cross-Site Scripting.

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