diff --git a/app/Http/Controllers/Api/ServersController.php b/app/Http/Controllers/Api/ServersController.php
index 6c3b2da00..2c2195ea3 100644
--- a/app/Http/Controllers/Api/ServersController.php
+++ b/app/Http/Controllers/Api/ServersController.php
@@ -13,6 +13,7 @@ use App\Models\PrivateKey;
 use App\Models\Project;
 use App\Models\Server as ModelsServer;
 use App\Rules\ValidServerIp;
+use App\Support\ValidationPatterns;
 use Illuminate\Http\JsonResponse;
 use Illuminate\Http\Request;
 use OpenApi\Attributes as OA;
@@ -487,10 +488,12 @@ class ServersController extends Controller
             'ip' => ['string', 'required', new ValidServerIp],
             'port' => 'integer|nullable|between:1,65535',
             'private_key_uuid' => 'string|required',
-            'user' => ['string', 'nullable', 'regex:/^[a-zA-Z0-9_-]+$/'],
+            'user' => ValidationPatterns::serverUsernameRules(required: false),
             'is_build_server' => 'boolean|nullable',
             'instant_validate' => 'boolean|nullable',
             'proxy_type' => 'string|nullable',
+        ], [
+            ...ValidationPatterns::serverUsernameMessages(),
         ]);
 
         $extraFields = array_diff(array_keys($request->all()), $allowedFields);
@@ -666,7 +669,7 @@ class ServersController extends Controller
             'ip' => ['string', 'nullable', new ValidServerIp],
             'port' => 'integer|nullable|between:1,65535',
             'private_key_uuid' => 'string|nullable',
-            'user' => ['string', 'nullable', 'regex:/^[a-zA-Z0-9_-]+$/'],
+            'user' => ValidationPatterns::serverUsernameRules(required: false),
             'is_build_server' => 'boolean|nullable',
             'instant_validate' => 'boolean|nullable',
             'proxy_type' => 'string|nullable',
@@ -676,6 +679,8 @@ class ServersController extends Controller
             'server_disk_usage_notification_threshold' => 'integer|min:1|max:100',
             'server_disk_usage_check_frequency' => 'string',
             'connection_timeout' => 'integer|min:1|max:300',
+        ], [
+            ...ValidationPatterns::serverUsernameMessages(),
         ]);
 
         $extraFields = array_diff(array_keys($request->all()), $allowedFields);
diff --git a/app/Livewire/Boarding/Index.php b/app/Livewire/Boarding/Index.php
index 33c75bf70..2d0ae939d 100644
--- a/app/Livewire/Boarding/Index.php
+++ b/app/Livewire/Boarding/Index.php
@@ -8,6 +8,7 @@ use App\Models\Project;
 use App\Models\Server;
 use App\Models\Team;
 use App\Services\ConfigurationRepository;
+use App\Support\ValidationPatterns;
 use Illuminate\Support\Collection;
 use Livewire\Attributes\Url;
 use Livewire\Component;
@@ -212,6 +213,23 @@ class Index extends Component
         }
     }
 
+    protected function rules(): array
+    {
+        return [
+            'remoteServerName' => 'required|string',
+            'remoteServerHost' => 'required|string',
+            'remoteServerPort' => 'required|integer|min:1|max:65535',
+            'remoteServerUser' => ValidationPatterns::serverUsernameRules(),
+        ];
+    }
+
+    protected function messages(): array
+    {
+        return [
+            ...ValidationPatterns::serverUsernameMessages('remoteServerUser', 'SSH User'),
+        ];
+    }
+
     public function getProxyType()
     {
         $this->selectProxy(ProxyTypes::TRAEFIK->value);
@@ -274,12 +292,7 @@ class Index extends Component
 
     public function saveServer()
     {
-        $this->validate([
-            'remoteServerName' => 'required|string',
-            'remoteServerHost' => 'required|string',
-            'remoteServerPort' => 'required|integer',
-            'remoteServerUser' => 'required|string',
-        ]);
+        $this->validate();
 
         $this->privateKey = formatPrivateKey($this->privateKey);
         $foundServer = Server::whereIp($this->remoteServerHost)->first();
@@ -465,10 +478,10 @@ class Index extends Component
 
     public function saveAndValidateServer()
     {
-        $this->validate([
-            'remoteServerPort' => 'required|integer|min:1|max:65535',
-            'remoteServerUser' => 'required|string',
-        ]);
+        $this->validate(array_intersect_key($this->rules(), array_flip([
+            'remoteServerPort',
+            'remoteServerUser',
+        ])));
 
         $this->createdServer->update([
             'port' => $this->remoteServerPort,
diff --git a/app/Livewire/Server/New/ByIp.php b/app/Livewire/Server/New/ByIp.php
index 51c6a06ee..f5ea2ae80 100644
--- a/app/Livewire/Server/New/ByIp.php
+++ b/app/Livewire/Server/New/ByIp.php
@@ -57,7 +57,7 @@ class ByIp extends Component
             'name' => ValidationPatterns::nameRules(),
             'description' => ValidationPatterns::descriptionRules(),
             'ip' => ['required', 'string', new ValidServerIp],
-            'user' => ['required', 'string', 'regex:/^[a-zA-Z0-9_-]+$/'],
+            'user' => ValidationPatterns::serverUsernameRules(),
             'port' => 'required|integer|between:1,65535',
             'is_build_server' => 'required|boolean',
         ];
@@ -75,6 +75,7 @@ class ByIp extends Component
             'ip.string' => 'The IP Address/Domain must be a string.',
             'user.required' => 'The User field is required.',
             'user.string' => 'The User field must be a string.',
+            ...ValidationPatterns::serverUsernameMessages(),
             'port.required' => 'The Port field is required.',
             'port.integer' => 'The Port field must be an integer.',
             'port.between' => 'The Port field must be between 1 and 65535.',
diff --git a/app/Livewire/Server/Show.php b/app/Livewire/Server/Show.php
index d7339dcdb..4a6e2335e 100644
--- a/app/Livewire/Server/Show.php
+++ b/app/Livewire/Server/Show.php
@@ -110,7 +110,7 @@ class Show extends Component
             'name' => ValidationPatterns::nameRules(),
             'description' => ValidationPatterns::descriptionRules(),
             'ip' => ['required', new ValidServerIp],
-            'user' => ['required', 'regex:/^[a-zA-Z0-9_-]+$/'],
+            'user' => ValidationPatterns::serverUsernameRules(),
             'port' => 'required|integer|between:1,65535',
             'connectionTimeout' => 'required|integer|min:1|max:300',
             'validationLogs' => 'nullable',
@@ -140,6 +140,7 @@ class Show extends Component
             [
                 'ip.required' => 'The IP Address field is required.',
                 'user.required' => 'The User field is required.',
+                ...ValidationPatterns::serverUsernameMessages(),
                 'port.required' => 'The Port field is required.',
                 'connectionTimeout.required' => 'The SSH Connection Timeout field is required.',
                 'connectionTimeout.integer' => 'The SSH Connection Timeout must be an integer.',
diff --git a/app/Models/Server.php b/app/Models/Server.php
index 74e8ba5b0..2b7bbac55 100644
--- a/app/Models/Server.php
+++ b/app/Models/Server.php
@@ -17,6 +17,7 @@ use App\Livewire\Server\Proxy;
 use App\Notifications\Server\Reachable;
 use App\Notifications\Server\Unreachable;
 use App\Services\ConfigurationRepository;
+use App\Support\ValidationPatterns;
 use App\Traits\ClearsGlobalSearchCache;
 use App\Traits\HasMetrics;
 use App\Traits\HasSafeStringAttribute;
@@ -945,10 +946,10 @@ $schema://$host {
     {
         return Attribute::make(
             get: function ($value) {
-                return preg_replace('/[^A-Za-z0-9\-_]/', '', $value);
+                return preg_replace(ValidationPatterns::INVALID_SERVER_USERNAME_CHARACTERS_PATTERN, '', $value);
             },
             set: function ($value) {
-                return preg_replace('/[^A-Za-z0-9\-_]/', '', $value);
+                return preg_replace(ValidationPatterns::INVALID_SERVER_USERNAME_CHARACTERS_PATTERN, '', $value);
             }
         );
     }
diff --git a/app/Support/ValidationPatterns.php b/app/Support/ValidationPatterns.php
index 7e3974dd7..bdb8654b9 100644
--- a/app/Support/ValidationPatterns.php
+++ b/app/Support/ValidationPatterns.php
@@ -35,6 +35,17 @@ class ValidationPatterns
      */
     public const DOCKER_TARGET_PATTERN = '/^[a-zA-Z0-9][a-zA-Z0-9._-]*$/';
 
+    /**
+     * Pattern for SSH usernames.
+     * Allows alphanumeric characters, dots, hyphens, and underscores.
+     */
+    public const SERVER_USERNAME_PATTERN = '/^[a-zA-Z0-9._-]+$/';
+
+    /**
+     * Pattern for removing characters not allowed in SSH usernames.
+     */
+    public const INVALID_SERVER_USERNAME_CHARACTERS_PATTERN = '/[^A-Za-z0-9.\-_]/';
+
     /**
      * Token-aware pattern for shell-safe command strings (docker compose commands, docker run options).
      *
@@ -283,6 +294,28 @@ class ValidationPatterns
         return $rules;
     }
 
+    /**
+     * Get validation rules for SSH username fields.
+     */
+    public static function serverUsernameRules(bool $required = true): array
+    {
+        return [
+            $required ? 'required' : 'nullable',
+            'string',
+            'regex:'.self::SERVER_USERNAME_PATTERN,
+        ];
+    }
+
+    /**
+     * Get validation messages for SSH username fields.
+     */
+    public static function serverUsernameMessages(string $field = 'user', string $label = 'User'): array
+    {
+        return [
+            "{$field}.regex" => "The {$label} may only contain letters, numbers, dots, hyphens, and underscores.",
+        ];
+    }
+
     /**
      * Get validation messages for database identifier fields.
      */
diff --git a/bootstrap/helpers/shared.php b/bootstrap/helpers/shared.php
index 08af8ee42..f2b672fef 100644
--- a/bootstrap/helpers/shared.php
+++ b/bootstrap/helpers/shared.php
@@ -1865,15 +1865,15 @@ function isBase64Encoded($strValue)
 {
     return base64_encode(base64_decode($strValue, true)) === $strValue;
 }
-function customApiValidator(Collection|array $item, array $rules)
+function customApiValidator(Collection|array $item, array $rules, array $messages = [])
 {
     if (is_array($item)) {
         $item = collect($item);
     }
 
-    return Validator::make($item->toArray(), $rules, [
+    return Validator::make($item->toArray(), $rules, array_merge([
         'required' => 'This field is required.',
-    ]);
+    ], $messages));
 }
 function parseDockerComposeFile(Service|Application $resource, bool $isNew = false, int $pull_request_id = 0, ?int $preview_id = null)
 {
diff --git a/resources/views/components/modal-input.blade.php b/resources/views/components/modal-input.blade.php
index 2860d25e6..dc1191b44 100644
--- a/resources/views/components/modal-input.blade.php
+++ b/resources/views/components/modal-input.blade.php
@@ -36,32 +36,34 @@
     <template x-teleport="body">
         <div x-show="modalOpen"
             x-init="$watch('modalOpen', value => { if(value) { $nextTick(() => { const firstInput = $el.querySelector('input, textarea, select'); firstInput?.focus(); }) } })"
-            class="fixed top-0 left-0 z-99 flex items-center justify-center w-screen h-screen p-4">
+            class="fixed inset-0 z-99 overflow-y-auto">
             <div x-show="modalOpen" x-transition:enter="ease-out duration-100" x-transition:enter-start="opacity-0"
                 x-transition:enter-end="opacity-100" x-transition:leave="ease-in duration-100"
                 x-transition:leave-start="opacity-100" x-transition:leave-end="opacity-0"
-                @if ($closeOutside) @click="modalOpen=false" @endif
                 class="absolute inset-0 w-full h-full bg-black/20 backdrop-blur-xs"></div>
-            <div id="{{ $modalId }}" x-show="modalOpen" x-trap.inert.noscroll="modalOpen"
-                x-transition:enter="ease-out duration-100"
-                x-transition:enter-start="opacity-0 -translate-y-2 sm:scale-95"
-                x-transition:enter-end="opacity-100 translate-y-0 sm:scale-100"
-                x-transition:leave="ease-in duration-100"
-                x-transition:leave-start="opacity-100 translate-y-0 sm:scale-100"
-                x-transition:leave-end="opacity-0 -translate-y-2 sm:scale-95"
-                class="relative w-full lg:w-auto lg:min-w-2xl lg:max-w-4xl border rounded-sm drop-shadow-sm bg-white border-neutral-200 dark:bg-base dark:border-coolgray-300 flex flex-col">
-                <div class="flex items-center justify-between py-6 px-6 shrink-0">
-                    <h3 class="text-2xl font-bold">{{ $title }}</h3>
-                    <button @click="modalOpen=false"
-                        class="absolute cursor-pointer top-0 right-0 flex items-center justify-center w-8 h-8 mt-5 mr-5 rounded-full dark:text-white hover:bg-neutral-100 dark:hover:bg-coolgray-300 outline-0 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-coollabs dark:focus-visible:ring-warning focus-visible:ring-offset-2 dark:focus-visible:ring-offset-base">
-                        <svg class="w-5 h-5" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24"
-                            stroke-width="1.5" stroke="currentColor">
-                            <path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
-                        </svg>
-                    </button>
-                </div>
-                <div class="relative flex items-center justify-center w-auto px-6 pb-6">
-                    {{ $slot }}
+            <div @if ($closeOutside) @click.self="modalOpen=false" @endif class="relative flex min-h-full items-start justify-center p-4 sm:items-center">
+                <div id="{{ $modalId }}" x-show="modalOpen" x-trap.inert.noscroll="modalOpen"
+                    x-transition:enter="ease-out duration-100"
+                    x-transition:enter-start="opacity-0 -translate-y-2 sm:scale-95"
+                    x-transition:enter-end="opacity-100 translate-y-0 sm:scale-100"
+                    x-transition:leave="ease-in duration-100"
+                    x-transition:leave-start="opacity-100 translate-y-0 sm:scale-100"
+                    x-transition:leave-end="opacity-0 -translate-y-2 sm:scale-95"
+                    class="relative flex max-h-[calc(100dvh-2rem)] w-full flex-col overflow-hidden rounded-sm border border-neutral-200 bg-white drop-shadow-sm dark:border-coolgray-300 dark:bg-base lg:w-auto lg:min-w-2xl lg:max-w-4xl">
+                    <div class="flex items-center justify-between py-6 px-6 shrink-0">
+                        <h3 class="text-2xl font-bold">{{ $title }}</h3>
+                        <button @click="modalOpen=false"
+                            class="absolute cursor-pointer top-0 right-0 flex items-center justify-center w-8 h-8 mt-5 mr-5 rounded-full dark:text-white hover:bg-neutral-100 dark:hover:bg-coolgray-300 outline-0 focus-visible:outline-none focus-visible:ring-2 focus-visible:ring-coollabs dark:focus-visible:ring-warning focus-visible:ring-offset-2 dark:focus-visible:ring-offset-base">
+                            <svg class="w-5 h-5" xmlns="http://www.w3.org/2000/svg" fill="none" viewBox="0 0 24 24"
+                                stroke-width="1.5" stroke="currentColor">
+                                <path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+                            </svg>
+                        </button>
+                    </div>
+                    <div class="relative min-h-0 flex-1 overflow-y-auto px-6 pb-6 pt-1"
+                        style="-webkit-overflow-scrolling: touch;">
+                        {{ $slot }}
+                    </div>
                 </div>
             </div>
         </div>
diff --git a/tests/Feature/ServerUsernameValidationTest.php b/tests/Feature/ServerUsernameValidationTest.php
new file mode 100644
index 000000000..4213ee21d
--- /dev/null
+++ b/tests/Feature/ServerUsernameValidationTest.php
@@ -0,0 +1,182 @@
+<?php
+
+use App\Livewire\Boarding\Index as BoardingIndex;
+use App\Livewire\Server\New\ByIp;
+use App\Models\InstanceSettings;
+use App\Models\PrivateKey;
+use App\Models\Server;
+use App\Models\Team;
+use App\Models\User;
+use Illuminate\Foundation\Testing\RefreshDatabase;
+use Livewire\Livewire;
+use Visus\Cuid2\Cuid2;
+
+uses(RefreshDatabase::class);
+
+beforeEach(function () {
+    config(['app.maintenance.driver' => 'file']);
+
+    InstanceSettings::forceCreate(['id' => 0, 'is_api_enabled' => true]);
+
+    $this->team = Team::factory()->create();
+    $this->user = User::factory()->create();
+    $this->team->members()->attach($this->user->id, ['role' => 'owner']);
+
+    session(['currentTeam' => $this->team]);
+
+    $this->privateKey = PrivateKey::withoutEvents(fn () => PrivateKey::forceCreate([
+        'uuid' => (string) new Cuid2,
+        'name' => 'Test SSH Key',
+        'description' => 'Test SSH Key',
+        'private_key' => 'test-private-key',
+        'team_id' => $this->team->id,
+    ]));
+
+    $token = $this->user->createToken('write-token', ['write']);
+    $token->accessToken->forceFill(['team_id' => $this->team->id])->save();
+    $this->token = $token->plainTextToken;
+});
+
+it('creates a server through the API with a dotted SSH username', function () {
+    $response = $this->withHeaders([
+        'Authorization' => 'Bearer '.$this->token,
+        'Content-Type' => 'application/json',
+    ])->postJson('/api/v1/servers', [
+        'name' => 'Dotted User Server',
+        'ip' => '192.0.2.10',
+        'private_key_uuid' => $this->privateKey->uuid,
+        'user' => 'deploy.user',
+    ]);
+
+    $response->assertCreated();
+    $this->assertDatabaseHas('servers', [
+        'ip' => '192.0.2.10',
+        'user' => 'deploy.user',
+    ]);
+});
+
+it('updates a server through the API with a dotted SSH username', function () {
+    $server = Server::factory()->create([
+        'team_id' => $this->team->id,
+        'private_key_id' => $this->privateKey->id,
+        'user' => 'deploy',
+    ]);
+
+    $response = $this->withHeaders([
+        'Authorization' => 'Bearer '.$this->token,
+        'Content-Type' => 'application/json',
+    ])->patchJson('/api/v1/servers/'.$server->uuid, [
+        'user' => 'deploy.user',
+    ]);
+
+    $response->assertStatus(201);
+    expect($server->fresh()->user)->toBe('deploy.user');
+});
+
+it('rejects unsafe SSH usernames when creating a server through the API', function () {
+    $response = $this->withHeaders([
+        'Authorization' => 'Bearer '.$this->token,
+        'Content-Type' => 'application/json',
+    ])->postJson('/api/v1/servers', [
+        'name' => 'Unsafe User Server',
+        'ip' => '192.0.2.11',
+        'private_key_uuid' => $this->privateKey->uuid,
+        'user' => 'deploy$user',
+    ]);
+
+    $response->assertStatus(422);
+    $response->assertJsonPath('errors.user.0', 'The User may only contain letters, numbers, dots, hyphens, and underscores.');
+});
+
+it('rejects unsafe SSH usernames through the API', function () {
+    $server = Server::factory()->create([
+        'team_id' => $this->team->id,
+        'private_key_id' => $this->privateKey->id,
+    ]);
+
+    $response = $this->withHeaders([
+        'Authorization' => 'Bearer '.$this->token,
+        'Content-Type' => 'application/json',
+    ])->patchJson('/api/v1/servers/'.$server->uuid, [
+        'user' => 'deploy$user',
+    ]);
+
+    $response->assertStatus(422);
+    $response->assertJsonStructure(['errors' => ['user']]);
+    $response->assertJsonPath('errors.user.0', 'The User may only contain letters, numbers, dots, hyphens, and underscores.');
+});
+
+it('allows dotted SSH usernames in the server creation form', function () {
+    $this->actingAs($this->user);
+
+    Livewire::test(ByIp::class, [
+        'private_keys' => collect([$this->privateKey]),
+        'limit_reached' => false,
+    ])
+        ->set('name', 'Dotted User Server')
+        ->set('ip', '192.0.2.20')
+        ->set('user', 'deploy.user')
+        ->set('private_key_id', $this->privateKey->id)
+        ->call('submit')
+        ->assertHasNoErrors(['user']);
+
+    $this->assertDatabaseHas('servers', [
+        'ip' => '192.0.2.20',
+        'user' => 'deploy.user',
+    ]);
+});
+
+it('rejects unsafe SSH usernames in the server creation form', function () {
+    $this->actingAs($this->user);
+
+    Livewire::test(ByIp::class, [
+        'private_keys' => collect([$this->privateKey]),
+        'limit_reached' => false,
+    ])
+        ->set('name', 'Unsafe User Server')
+        ->set('ip', '192.0.2.21')
+        ->set('user', 'deploy$user')
+        ->set('private_key_id', $this->privateKey->id)
+        ->call('submit')
+        ->assertHasErrors(['user' => ['regex']]);
+});
+
+it('rejects unsafe SSH usernames during onboarding server creation', function () {
+    $this->actingAs($this->user);
+
+    Livewire::test(BoardingIndex::class)
+        ->set('createdPrivateKey', $this->privateKey)
+        ->set('remoteServerName', 'Unsafe User Server')
+        ->set('remoteServerHost', '192.0.2.30')
+        ->set('remoteServerPort', 22)
+        ->set('remoteServerUser', 'deploy$user')
+        ->call('saveServer')
+        ->assertHasErrors([
+            'remoteServerUser' => [
+                'regex',
+                'The SSH User may only contain letters, numbers, dots, hyphens, and underscores.',
+            ],
+        ]);
+});
+
+it('rejects unsafe SSH usernames during onboarding server validation', function () {
+    $this->actingAs($this->user);
+
+    $server = Server::factory()->create([
+        'team_id' => $this->team->id,
+        'private_key_id' => $this->privateKey->id,
+        'user' => 'deploy',
+    ]);
+
+    Livewire::test(BoardingIndex::class)
+        ->set('createdServer', $server)
+        ->set('remoteServerPort', 22)
+        ->set('remoteServerUser', 'deploy$user')
+        ->call('saveAndValidateServer')
+        ->assertHasErrors([
+            'remoteServerUser' => [
+                'regex',
+                'The SSH User may only contain letters, numbers, dots, hyphens, and underscores.',
+            ],
+        ]);
+});
diff --git a/tests/Unit/ServerUsernamePatternTest.php b/tests/Unit/ServerUsernamePatternTest.php
new file mode 100644
index 000000000..dab3f05a8
--- /dev/null
+++ b/tests/Unit/ServerUsernamePatternTest.php
@@ -0,0 +1,19 @@
+<?php
+
+use App\Models\Server;
+use App\Support\ValidationPatterns;
+
+it('provides shared validation rules for SSH usernames', function () {
+    expect(ValidationPatterns::SERVER_USERNAME_PATTERN)->toBe('/^[a-zA-Z0-9._-]+$/');
+    expect(ValidationPatterns::serverUsernameRules())->toContain('regex:'.ValidationPatterns::SERVER_USERNAME_PATTERN);
+
+    expect(preg_match(ValidationPatterns::SERVER_USERNAME_PATTERN, 'deploy.user'))->toBe(1);
+    expect(preg_match(ValidationPatterns::SERVER_USERNAME_PATTERN, 'deploy$user'))->toBe(0);
+});
+
+it('preserves dots when sanitizing server SSH usernames', function () {
+    $server = new Server;
+    $server->user = 'deploy.user';
+
+    expect($server->user)->toBe('deploy.user');
+});