CVE-2026-122053sensiolabs symfony mass assignment

What it is

A request can set object fields it should not, such as a role or owner.

How it is reached

An attacker can exploit it over the network, without an account, and nobody has to click anything.

What an attacker gains

The direct impact is limited: partial access to data or a partial outage. In practice, this kind of flaw lets an attacker reach data or actions their role should not allow.

Is it being exploited?

There is no public report of exploitation yet. It can be exploited automatically, at scale.

What to do

1. No fixed version is listed yet. Find every place sensiolabs symfony runs, watch the references for a fix, and plan a replacement if it is no longer supported.
2. While there is no fix, keep it off the internet or behind a VPN, allowlist or authenticating proxy.

Description from NVD

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.