The Symfony Serializer component ObjectNormalizer treats any attribute name containing . (and, from Symfony 6.4, [) as a writable property path, allowing untrusted input to modify properties of nested objects and bypass their #[Ignore] metadata attribute in Symfony versions 5.4.41 prior to 5.4.56, 6.4.9 prior to 6.4.50, 7.0.9 prior to 7.1.0, 7.1.2 prior to 7.4.23, and 8.x prior to 8.1.11.
ObjectNormalizer::isAllowedAttribute() accepts such names, and setAttributeValue() hands the name straight to PropertyAccessor::setValue(), which parses it as a property path and traverses into the nested object. A payload key such as customer.admin writes to $order->customer->admin. The #[Ignore] metadata attribute is only consulted when the nested object is denormalized in its own right, never when it is reached through a path. #[Groups] restrictions are not bypassed: the path is only accepted when no groups are passed in the context, and then groups restrict nothing. When the root class carries neither #[Ignore] nor #[Groups], no allowlist applies and every key of the payload is let through. Because PropertyAccessor also resolves a path segment against public methods, a segment matching a public method name invokes that method with the attacker’s value.Applications that bind untrusted input to objects are affected, including controllers using #[MapRequestPayload] or #[MapQueryString], whose default normalizer is ObjectNormalizer. With OBJECT_TO_POPULATE, as used for partial updates, the traversal reaches an already hydrated entity graph, and the modified field may be persisted.
The fix accepts a property path only when the class metadata declares an attribute of that exact name. Declared paths keep working unchanged, and a path in the payload with no matching declaration is ignored.
CVE-2026-118515 is a high-severity vulnerability in the Symfony Serializer component affecting versions prior to 5.4.56, 6.4.50, 7.4.23, and 8.1.11. It allows an attacker to craft a request that causes the application to treat arbitrary files on the server as uploaded files without actual upload, potentially exposing or moving sensitive files. This occurs because the DataUriNormalizer only handles specific types, and subclasses like UploadedFile can be instantiated with attacker-controlled paths, bypassing normal upload checks.
CVE-2026-121623 is a high-severity vulnerability in the Symfony Serializer component affecting versions prior to 5.4.56, 6.4.50, 7.4.23, and 8.1.11. It allows arbitrary local file read via path traversal due to case-sensitive matching of the data: URI scheme in DataUriNormalizer::denormalize(). This flaw enables an attacker to bypass scheme validation by using uppercase schemes like DATA:, causing the application to treat the input as a local file path and read files accessible to the server. Exploitation requires sending a crafted request to an endpoint that deserializes untrusted input into file-related types, with no authentication needed if the endpoint is public.