diff --git a/app/Http/Controllers/Apis/Protected/Summit/OAuth2SummitApiController.php b/app/Http/Controllers/Apis/Protected/Summit/OAuth2SummitApiController.php
index d552bc377..19aa0bd1e 100644
--- a/app/Http/Controllers/Apis/Protected/Summit/OAuth2SummitApiController.php
+++ b/app/Http/Controllers/Apis/Protected/Summit/OAuth2SummitApiController.php
@@ -2529,7 +2529,7 @@ public function updateLeadReportSettings($summit_id) {
                 in: 'path',
                 required: true,
                 schema: new OA\Schema(type: 'string'),
-                description: 'RAW Badge QR scan encoded on BASE 64'
+                description: 'RAW Badge QR scan encoded on BASE 64 (standard RFC 4648 §4 or URL-safe §5 alphabet)'
             )
         ],
         responses: [
diff --git a/app/Utils/Base64.php b/app/Utils/Base64.php
index 2a742e170..3fd518851 100644
--- a/app/Utils/Base64.php
+++ b/app/Utils/Base64.php
@@ -17,10 +17,15 @@ final class Base64
     public static function looksLikeBase64(string $s): bool
     {
         if ($s === '') return false;
-        // Solo alfabeto base64 y '=' de padding
-        if (!preg_match('#^[A-Za-z0-9+/]*={0,2}$#', $s)) return false;
-        // Longitud múltiplo de 4 (permitimos sin padding, lo añadimos abajo)
-        return (strlen($s) % 4) === 0 || (strlen($s) % 4) === 2 || (strlen($s) % 4) === 3;
+        // Standard base64 alphabet (RFC 4648 §4) or URL-safe (§5: '-' and '_'), plus '=' padding
+        if (!preg_match('#^[A-Za-z0-9+/_-]*={0,2}$#', $s)) return false;
+        // Padding may be omitted entirely (it gets added below), but when present it must be
+        // exactly what the data length requires (RFC 4648)
+        $unpadded = rtrim($s, '=');
+        $paddingLength = strlen($s) - strlen($unpadded);
+        $remainder = strlen($unpadded) % 4;
+        if ($unpadded === '' || $remainder === 1) return false;
+        return $paddingLength === 0 || $paddingLength === (4 - $remainder);
     }
 
     public static function padBase64(string $s): string
@@ -31,6 +36,11 @@ public static function padBase64(string $s): string
 
     public static function tryBase64Decode(string $s): ?string
     {
+        // agree with the sniff: base64_decode('', true) "succeeds" with '' and would silently
+        // repair under-padded input, so anything looksLikeBase64 rejects is not decodable here
+        if (!self::looksLikeBase64($s)) return null;
+        // strict base64_decode rejects the URL-safe alphabet: normalize it first
+        $s = strtr($s, '-_', '+/');
         $padded = self::padBase64($s);
         $decoded = base64_decode($padded, true);
         return ($decoded === false) ? null : $decoded;
diff --git a/tests/Base64Test.php b/tests/Base64Test.php
new file mode 100644
index 000000000..6ea934c1f
--- /dev/null
+++ b/tests/Base64Test.php
@@ -0,0 +1,83 @@
+<?php namespace Tests;
+
+/**
+ * Copyright 2026 OpenStack Foundation
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ * http://www.apache.org/licenses/LICENSE-2.0
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ **/
+
+use App\Utils\Base64;
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Class Base64Test
+ * Badge/ticket QR artifacts travel base64-encoded as a URL path segment; the standard
+ * alphabet's "/" can never survive path routing (Laravel rawurldecodes the path before
+ * matching), so the helper must also accept the URL-safe alphabet (base64url, RFC 4648 §5:
+ * "-" for "+", "_" for "/"). Standard base64 must keep decoding byte-identical.
+ */
+final class Base64Test extends TestCase
+{
+    public function testStandardAlphabetStillDecodes()
+    {
+        // "+/+/" = indices 62,63,62,63 = bytes FB FF BF (hand-derived from the RFC 4648 table)
+        $this->assertTrue(Base64::looksLikeBase64("+/+/"));
+        $this->assertSame("\xfb\xff\xbf", Base64::tryBase64Decode("+/+/"));
+    }
+
+    public function testUrlSafeAlphabetIsAccepted()
+    {
+        // same payload as "+/+/", url-safe spelling
+        $this->assertTrue(Base64::looksLikeBase64("-_-_"));
+        $this->assertSame("\xfb\xff\xbf", Base64::tryBase64Decode("-_-_"));
+    }
+
+    public function testUrlSafeAndStandardSpellingsDecodeToTheSameBytes()
+    {
+        $standard = Base64::tryBase64Decode("QUFB/QkJC+Q0PT0=");
+        $urlSafe  = Base64::tryBase64Decode("QUFB_QkJC-Q0PT0=");
+        $this->assertNotNull($standard);
+        $this->assertSame($standard, $urlSafe);
+    }
+
+    public function testUrlSafeWithoutPaddingIsPadded()
+    {
+        // "-_" = indices 62,63 = 11111011 = byte FB after padding to "-_=="
+        $this->assertTrue(Base64::looksLikeBase64("-_"));
+        $this->assertSame("\xfb", Base64::tryBase64Decode("-_"));
+    }
+
+    public function testNonBase64InputIsRejected()
+    {
+        $this->assertFalse(Base64::looksLikeBase64("BADGE_X|123|a@b.com|Ada Lovelace"));
+        $this->assertFalse(Base64::looksLikeBase64(""));
+        $this->assertNull(Base64::tryBase64Decode("!!!"));
+        // tryBase64Decode must agree with looksLikeBase64: base64_decode('', true) "succeeds"
+        // with '' but an empty artifact is not a decodable payload
+        $this->assertNull(Base64::tryBase64Decode(""));
+    }
+
+    public function testMalformedPaddingIsRejected()
+    {
+        // padding-only, under-padded and over-padded inputs are not RFC 4648 base64: the data
+        // length (minus padding) decides how much padding is allowed - none, or exactly enough
+        // to reach a multiple of 4
+        $this->assertFalse(Base64::looksLikeBase64("=="));
+        $this->assertFalse(Base64::looksLikeBase64("A="));
+        $this->assertFalse(Base64::looksLikeBase64("QQ="));
+        $this->assertFalse(Base64::looksLikeBase64("QUFB=="));
+        // the decode agrees with the sniff: what looksLikeBase64 rejects, tryBase64Decode
+        // rejects too (no silent repair of under-padded input)
+        $this->assertNull(Base64::tryBase64Decode("QQ="));
+        // exact RFC padding stays accepted
+        $this->assertTrue(Base64::looksLikeBase64("QQQ="));
+        $this->assertSame("A\x04", Base64::tryBase64Decode("QQQ="));
+    }
+}