API Platform Core vulnerable to cross-user attribute leak in JSON:API and HAL item normalizers due to missing isCacheKeySafe gate

Impact

#[ApiProperty(security: ...)] is evaluated per request to decide whether a property is exposed. The componentsCache arrays in ApiPlatform\JsonApi\Serializer\ItemNormalizer and ApiPlatform\Hal\Serializer\ItemNormalizer are keyed on $context['cache_key'], which is set unconditionally before delegating to the parent normalizer. The component structure (attributes, relationships, links) computed for one request can therefore be reused for a subsequent request whose user has a different set of accessible properties. A user with lower privileges may end up seeing the structure of properties that the security predicate would otherwise have hidden for them.

This is the same vulnerability class as GHSA-428q-q3vv-3fq3 / CVE-2025-31485, which fixed only the GraphQL ItemNormalizer. The JSON:API and HAL paths were not addressed at the time.

Exploitation conditions

Exploitation requires all of the following to coincide:

• The application exposes a resource via the JSON:API and/or HAL formats.
• At least one property of that resource uses #[ApiProperty(security: ...)] with a predicate whose result depends on the current user (or on per-request state).
• A request from a user for whom the predicate evaluates to true populates componentsCache before a request from a user for whom the predicate evaluates to false, within the lifetime of the same PHP process.
• The deployment uses a long-running PHP runtime that keeps the normalizer instance alive across requests (FrankenPHP worker mode, RoadRunner, Swoole, ReactPHP, etc.). With classic php-fpm workers the cache only survives the duration of a single request, which makes the issue much harder to observe in practice.

Patches

• 4.1.29
• 4.2.25
• 4.3.8

All three branches receive patched releases of api-platform/core, api-platform/json-api, and api-platform/hal.

Workarounds

Override the JSON:API and HAL ItemNormalizer services to gate $context['cache_key'] with a resource-class security check, or avoid #[ApiProperty(security: ...)] on resources served as JSON:API or HAL until the patch is applied. Pinning the deployment to classic php-fpm workers also limits exposure since the cache does not survive across requests.

Credits

• Tillmann Baumgart (@tillmon) — originally identified the broader cache-key gap and proposed moving isCacheKeySafe to AbstractItemNormalizer.
• Antoine Bluchet (@soyuka) — extended the gate to JSON:API and HAL normalizers.