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Review: Theme Negotiation by Rules (SA-CONTRIB-2026-012) CSRF Advisory and Hardening Steps

· 2 min read
Victor Jimenez
Victor Jimenez
Software Engineer & AI Agent Builder

On February 25, 2026, Drupal published SA-CONTRIB-2026-012 for Theme Negotiation by Rules (drupal/theme_rule), tracked as CVE-2026-3211.

The vulnerability is a CSRF issue in enable/disable actions for theme rules, triggered through GET requests.

Advisory Snapshot​

  • Project: Theme Negotiation by Rules
  • Advisory: SA-CONTRIB-2026-012
  • CVE: CVE-2026-3211
  • Date: 2026-02-25
  • Risk: Moderately critical (13/25)
  • Affected versions: <1.2.1
  • Fixed version: 1.2.1

Primary impact: An attacker can trick an administrator into toggling theme rules by visiting a crafted link. Integrity is affected because rule state can be changed.

Why This Matters​

Theme-rule state drives which theme renders specific routes or request patterns. If those rules are unexpectedly enabled or disabled, users can receive the wrong presentation layer, and operational behavior can drift from approved config.

This is not data exfiltration, but it is still a real admin-action integrity problem and should be treated as a security update, not just a bugfix.

Hardening Steps (Practical)​

  1. Update immediately to the fixed release.
composer require drupal/theme_rule:^1.2.1
drush updb -y
drush cr
  1. Enforce CSRF-safe admin patterns in custom code:
  • No state-changing operations on GET routes.
  • Require POST for state changes.
  • Validate CSRF tokens on every mutating action.
  • Keep access checks explicit for admin operations.
  1. Reduce blast radius:
  • Limit who has permissions to administer theme-rule entities.
  • Review permission assignments for broad admin-like roles.
  • Add log alerts for unexpected theme-rule enable/disable changes.
  1. Add regression tests to your own modules:
  • Functional test: GET request must not mutate rule state.
  • Functional test: POST without token must be denied.
  • Functional test: POST with valid token performs expected change.
  1. Add process controls:
  • Subscribe to Drupal security advisories and triage within 24 hours.
  • Require security-check steps in deployment checklists for contrib updates.

Quick Verification Checklist​

  • composer show drupal/theme_rule reports 1.2.1 or newer.
  • No custom routes mutate config/entity state via GET.
  • Admin actions that mutate state require POST + CSRF token.
  • Recent logs show no unexplained theme-rule toggles.

Sources​