diff --git a/src/DataCollection/KeyValueDataFilter.php b/src/DataCollection/KeyValueDataFilter.php
new file mode 100644
index 000000000..c90c6d5ab
--- /dev/null
+++ b/src/DataCollection/KeyValueDataFilter.php
@@ -0,0 +1,171 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\DataCollection;
+
+/**
+ * @internal
+ *
+ * @phpstan-type KeyValueCollectionBehavior array{mode: 'off'|'denyList'|'allowList', terms: string[]}
+ */
+final class KeyValueDataFilter
+{
+    private const SENSITIVE_DATA_DENYLIST = [
+        'auth',
+        'token',
+        'secret',
+        'password',
+        'passwd',
+        'pwd',
+        'key',
+        'jwt',
+        'bearer',
+        'sso',
+        'saml',
+        'csrf',
+        'xsrf',
+        'credentials',
+        'session',
+        'sid',
+        'identity',
+    ];
+
+    /**
+     * Cookie headers that must always be filtered when headers are collected.
+     */
+    private const SENSITIVE_HEADERS = [
+        'cookie',
+        'set-cookie',
+    ];
+
+    /**
+     * @var string|null
+     */
+    private static $sensitiveDataDenyListRegex;
+
+    private function __construct()
+    {
+    }
+
+    /**
+     * @param array<array-key, string[]> $headers
+     *
+     * @phpstan-param KeyValueCollectionBehavior $behavior
+     *
+     * @return array<string, string[]>|null Returns null when collection is off
+     */
+    public static function filterHeaders(array $headers, array $behavior): ?array
+    {
+        if ($behavior['mode'] === 'off') {
+            return null;
+        }
+
+        $filtered = [];
+
+        foreach ($headers as $name => $values) {
+            $name = (string) $name;
+
+            if (\in_array(strtolower($name), self::SENSITIVE_HEADERS, true) || self::shouldFilterValue($name, $behavior)) {
+                foreach ($values as $headerLine => $headerValue) {
+                    $values[$headerLine] = '[Filtered]';
+                }
+            }
+
+            $filtered[$name] = $values;
+        }
+
+        return $filtered;
+    }
+
+    /**
+     * @param array<array-key, mixed> $data
+     *
+     * @phpstan-param KeyValueCollectionBehavior $behavior
+     *
+     * @return array<string, mixed>|null Returns null when collection is off
+     */
+    public static function filterKeyValueData(array $data, array $behavior): ?array
+    {
+        if ($behavior['mode'] === 'off') {
+            return null;
+        }
+
+        $filtered = [];
+
+        /** @mago-ignore analysis:mixed-assignment */
+        foreach ($data as $key => $value) {
+            $key = (string) $key;
+            $filtered[$key] = self::shouldFilterValue($key, $behavior) ? '[Filtered]' : $value;
+        }
+
+        return $filtered;
+    }
+
+    /**
+     * @phpstan-param KeyValueCollectionBehavior $behavior
+     */
+    public static function filterQueryString(string $queryString, array $behavior): ?string
+    {
+        if ($behavior['mode'] === 'off') {
+            return null;
+        }
+
+        $parts = explode('&', $queryString);
+
+        foreach ($parts as $index => $part) {
+            $separatorPosition = strpos($part, '=');
+            $encodedKey = $separatorPosition === false ? $part : substr($part, 0, $separatorPosition);
+            $key = urldecode($encodedKey);
+
+            if (self::shouldFilterValue($key, $behavior)) {
+                $parts[$index] = $encodedKey . '=[Filtered]';
+            }
+        }
+
+        return implode('&', $parts);
+    }
+
+    /**
+     * @phpstan-param KeyValueCollectionBehavior $behavior
+     */
+    private static function shouldFilterValue(string $key, array $behavior): bool
+    {
+        if (self::matchesMandatoryDenyList($key)) {
+            return true;
+        }
+
+        if ($behavior['mode'] === 'allowList') {
+            return !self::matchesAnyTerm($key, $behavior['terms']);
+        }
+
+        return self::matchesAnyTerm($key, $behavior['terms']);
+    }
+
+    private static function matchesMandatoryDenyList(string $key): bool
+    {
+        if (self::$sensitiveDataDenyListRegex === null) {
+            self::$sensitiveDataDenyListRegex = '/' . implode('|', array_map(static function (string $term): string {
+                return preg_quote($term, '/');
+            }, self::SENSITIVE_DATA_DENYLIST)) . '/i';
+        }
+
+        return preg_match(self::$sensitiveDataDenyListRegex, $key) === 1;
+    }
+
+    /**
+     * @param string[] $terms
+     */
+    private static function matchesAnyTerm(string $key, array $terms): bool
+    {
+        $key = strtolower($key);
+
+        foreach ($terms as $term) {
+            if (strpos($key, strtolower($term)) !== false) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+}
diff --git a/tests/DataCollection/KeyValueDataFilterTest.php b/tests/DataCollection/KeyValueDataFilterTest.php
new file mode 100644
index 000000000..2662102cb
--- /dev/null
+++ b/tests/DataCollection/KeyValueDataFilterTest.php
@@ -0,0 +1,186 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Sentry\Tests\DataCollection;
+
+use PHPUnit\Framework\TestCase;
+use Sentry\DataCollection\KeyValueDataFilter;
+
+final class KeyValueDataFilterTest extends TestCase
+{
+    public function testFilterKeyValueDataReturnsNullWhenCollectionIsOff(): void
+    {
+        $behavior = ['mode' => 'off', 'terms' => ['public']];
+
+        $this->assertNull(KeyValueDataFilter::filterKeyValueData([
+            'authorization' => 'secret',
+            'public' => 'visible',
+        ], $behavior));
+    }
+
+    public function testFilterKeyValueDataAppliesMandatoryDenyList(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => []];
+
+        $filtered = KeyValueDataFilter::filterKeyValueData([
+            'AUTHORIZATION' => 'secret',
+            'public' => 'visible',
+        ], $behavior);
+
+        $this->assertSame([
+            'AUTHORIZATION' => '[Filtered]',
+            'public' => 'visible',
+        ], $filtered);
+    }
+
+    public function testFilterKeyValueDataCombinesMandatoryAndCustomDenyListTerms(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => ['custom']];
+
+        $filtered = KeyValueDataFilter::filterKeyValueData([
+            'authorization' => 'secret',
+            'custom-field' => 'private',
+            'public' => 'visible',
+        ], $behavior);
+
+        $this->assertSame([
+            'authorization' => '[Filtered]',
+            'custom-field' => '[Filtered]',
+            'public' => 'visible',
+        ], $filtered);
+    }
+
+    public function testFilterKeyValueDataAppliesAllowList(): void
+    {
+        $behavior = ['mode' => 'allowList', 'terms' => ['theme']];
+
+        $filtered = KeyValueDataFilter::filterKeyValueData([
+            'preferred-theme' => 'dark',
+            'tracking_id' => '12345',
+        ], $behavior);
+
+        $this->assertSame([
+            'preferred-theme' => 'dark',
+            'tracking_id' => '[Filtered]',
+        ], $filtered);
+    }
+
+    public function testFilterKeyValueDataAllowListCannotOverrideMandatoryDenyList(): void
+    {
+        $behavior = ['mode' => 'allowList', 'terms' => ['authorization']];
+
+        $filtered = KeyValueDataFilter::filterKeyValueData([
+            'authorization' => 'secret',
+        ], $behavior);
+
+        $this->assertSame(['authorization' => '[Filtered]'], $filtered);
+    }
+
+    public function testFilterHeadersReturnsNullWhenCollectionIsOff(): void
+    {
+        $behavior = ['mode' => 'off', 'terms' => ['x-request-id']];
+
+        $this->assertNull(KeyValueDataFilter::filterHeaders([
+            'Authorization' => ['secret'],
+            'X-Request-Id' => ['request-id'],
+        ], $behavior));
+    }
+
+    public function testFilterHeadersAppliesDenyListToEveryHeaderLine(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => []];
+
+        $filtered = KeyValueDataFilter::filterHeaders([
+            'X-Api-Key' => ['first', 'second'],
+            'X-Request-Id' => ['request-id'],
+        ], $behavior);
+
+        $this->assertSame([
+            'X-Api-Key' => ['[Filtered]', '[Filtered]'],
+            'X-Request-Id' => ['request-id'],
+        ], $filtered);
+    }
+
+    public function testFilterHeadersAlwaysFiltersCookieHeaders(): void
+    {
+        $behavior = ['mode' => 'allowList', 'terms' => ['cookie', 'set-cookie', 'x-request-id']];
+
+        $filtered = KeyValueDataFilter::filterHeaders([
+            'Cookie' => ['session_id=secret; theme=dark'],
+            'Set-Cookie' => ['session_id=secret'],
+            'X-Request-Id' => ['request-id'],
+        ], $behavior);
+
+        $this->assertSame([
+            'Cookie' => ['[Filtered]'],
+            'Set-Cookie' => ['[Filtered]'],
+            'X-Request-Id' => ['request-id'],
+        ], $filtered);
+    }
+
+    public function testFilterHeadersAppliesExtendedDenyTerms(): void
+    {
+        $defaultBehavior = ['mode' => 'denyList', 'terms' => []];
+        $extendedBehavior = ['mode' => 'denyList', 'terms' => ['forwarded', '-ip', 'remote-', 'via', '-user']];
+        $headers = [
+            'X-Forwarded-For' => ['203.0.113.7'],
+            'X-Real-IP' => ['203.0.113.7'],
+        ];
+
+        $this->assertSame($headers, KeyValueDataFilter::filterHeaders($headers, $defaultBehavior));
+        $this->assertSame([
+            'X-Forwarded-For' => ['[Filtered]'],
+            'X-Real-IP' => ['[Filtered]'],
+        ], KeyValueDataFilter::filterHeaders($headers, $extendedBehavior));
+    }
+
+    public function testFilterHeadersAppliesAllowList(): void
+    {
+        $behavior = ['mode' => 'allowList', 'terms' => ['request-id']];
+
+        $filtered = KeyValueDataFilter::filterHeaders([
+            'X-Request-Id' => ['request-id'],
+            'Host' => ['example.com'],
+        ], $behavior);
+
+        $this->assertSame([
+            'X-Request-Id' => ['request-id'],
+            'Host' => ['[Filtered]'],
+        ], $filtered);
+    }
+
+    public function testFilterQueryStringReturnsNullWhenCollectionIsOff(): void
+    {
+        $behavior = ['mode' => 'off', 'terms' => ['page']];
+
+        $this->assertNull(KeyValueDataFilter::filterQueryString('token=secret&page=1', $behavior));
+    }
+
+    public function testFilterQueryStringAppliesMandatoryAndCustomDenyListTerms(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => ['page']];
+
+        $filtered = KeyValueDataFilter::filterQueryString('token=secret&page=1&flag', $behavior);
+
+        $this->assertSame('token=[Filtered]&page=[Filtered]&flag', $filtered);
+    }
+
+    public function testFilterQueryStringDecodesKeysBeforeMatching(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => []];
+
+        $filtered = KeyValueDataFilter::filterQueryString('api%5Ftoken=secret&page=1', $behavior);
+
+        $this->assertSame('api%5Ftoken=[Filtered]&page=1', $filtered);
+    }
+
+    public function testFilterQueryStringDoesNotTreatCookieNamesAsCookieHeaders(): void
+    {
+        $behavior = ['mode' => 'denyList', 'terms' => []];
+
+        $filtered = KeyValueDataFilter::filterQueryString('cookie=foo&set-cookie=bar', $behavior);
+
+        $this->assertSame('cookie=foo&set-cookie=bar', $filtered);
+    }
+}