CVE-2026-77135: Frontend User Extension Info Disclosure Flaw

CVE-2026-77135 Overview

CVE-2026-77135 is an Insecure Direct Object Reference (IDOR) vulnerability [CWE-639] affecting a TYPO3 extension that provides Detail and List plugins for frontend user records. The extension's user detail view does not verify that the requested user record matches the configured or logged-in target. An unauthenticated visitor can supply an arbitrary user ID and retrieve another frontend user's profile, including name, email address, date of birth, and postal address. The flaw is documented in TYPO3 Security Advisory 2026-024.

Critical Impact
Any network-based visitor with access to the Detail or List plugin can enumerate and exfiltrate personally identifiable information (PII) belonging to frontend users without authentication.

Affected Products

TYPO3 third-party extension providing frontend user Detail and List plugins (see TYPO3-EXT-SA-2026-024)
Deployments exposing the vulnerable Detail or List plugin to public visitors
TYPO3 installations that store frontend user profile data (fe_users) accessible through the extension

Discovery Timeline

2026-08-25 - CVE-2026-77135 published to NVD
2026-08-26 - Last updated in NVD database

Technical Details for CVE-2026-77135

Vulnerability Analysis

The vulnerability is a classic authorization failure on a resource identifier. The Detail plugin accepts a user ID parameter from the request and loads the corresponding fe_users record without checking whether the caller is entitled to view it. The List plugin exposes the same behavior when rendering profile links. Because the check against the configured target user or the currently logged-in frontend user is missing, any visitor can substitute an arbitrary ID and retrieve the record.

The returned dataset includes identifying and contact fields such as name, email, date of birth, and address. This makes the flaw an information disclosure issue with direct privacy impact under regimes such as GDPR. The vulnerability is exploitable over the network without prior authentication and requires no user interaction.

Root Cause

The root cause is a missing authorization check between the caller and the target object [CWE-639]. The controller trusts the client-supplied identifier and does not compare it to the plugin's configured user ID or to the frontend user session context. Access control decisions rely on the presence of the plugin rather than on ownership of the data.

Attack Vector

An attacker browses to any page hosting the Detail or List plugin and modifies the user ID parameter in the query string or form data. Iterating through sequential IDs enables full enumeration of the fe_users table exposed by the extension. Automated scraping is straightforward because responses render structured profile fields in the page HTML. No credentials, tokens, or elevated privileges are needed.

No verified proof-of-concept code is available. See the TYPO3 Security Advisory 2026-024 for vendor technical details.

Detection Methods for CVE-2026-77135

Indicators of Compromise

Web server access logs showing repeated requests to pages containing the Detail or List plugin with varying numeric user ID parameters from a single client or IP range.
Sequential or fuzzed values in the plugin's user ID request parameter, indicative of enumeration.
Unusual outbound response sizes from the vulnerable endpoint correlated with high-volume GET requests.

Detection Strategies

Parse HTTP access logs for the vulnerable plugin route and alert on more than N distinct user ID values requested by the same source within a short window.
Deploy a WAF rule that inspects the user ID parameter and blocks requests where the ID does not match the plugin's configured value or session-bound frontend user.
Review TYPO3 audit logs for anomalous fe_users record reads originating from anonymous sessions.

Monitoring Recommendations

Baseline normal request volume to pages hosting the Detail and List plugins and alert on statistical deviations.
Monitor egress traffic for large HTML responses from frontend user profile pages to unauthenticated clients.
Correlate scraping-style user-agent strings and IP reputation feeds with hits on the vulnerable endpoint.

How to Mitigate CVE-2026-77135

Immediate Actions Required

Apply the fixed version of the affected TYPO3 extension as identified in TYPO3 Security Advisory 2026-024.
Temporarily remove or disable the Detail and List plugins on public-facing pages until the patch is deployed.
Audit web server and TYPO3 logs for prior enumeration activity and notify affected frontend users if PII exposure is confirmed.

Patch Information

Refer to TYPO3 Security Advisory 2026-024 for the specific extension name, affected version ranges, and fixed release. Update the extension through the TYPO3 Extension Manager or Composer and clear all caches after installation. Verify that the patched controller enforces a strict comparison between the requested user ID and the configured or authenticated target.

Workarounds

Restrict the vulnerable plugin to authenticated pages protected by TYPO3 access controls until patched.
Configure the plugin to render only the currently logged-in frontend user and ignore client-supplied IDs where the extension supports that mode.
Deploy a reverse proxy or WAF rule that strips or validates the user ID parameter against the expected value.
Rate-limit requests to pages hosting the Detail and List plugins to slow enumeration attempts.

bash

# Example nginx rule to block requests with unexpected user ID values
# Adjust the parameter name and allowed value to match the extension configuration
location ~* /path/to/plugin/page {
    if ($arg_user_id !~ "^(42)$") {
        return 403;
    }
}