CVE-2021-23727: 
Celery vulnerability analysis and mitigation

CVE-2021-23727 affects the Celery package versions before 5.2.2. The vulnerability stems from the package's default behavior of trusting messages and metadata stored in backends (result stores). When reading task metadata from the backend, the data is deserialized without proper validation (CVE Mitre, NVD).

The vulnerability exists in the exceptiontopython function within the celery.backends.base.Backend class. The function performs recursive attribute lookup based on a Python dotted path, where an arbitrary module reference is accessed based on properties from a deserialized JSON object stored in the Celery backend. The vulnerability allows for arbitrary attribute access and method calling with user-controlled arguments (Snyk Blog).

If exploited, an attacker who can gain access to or manipulate the metadata within a Celery backend could trigger a stored command injection vulnerability and potentially gain further access to the system. For systems utilizing Celery, this could lead to command injection within the producer, potentially allowing for total system takeover. In scenarios where the Celery backend is remote, attackers could move laterally within an organization's network and gain additional footholds (Snyk Blog).

The vulnerability was fixed in Celery version 5.2.2 by adding validation of the targeted module and checking the types of resolved attributes before calling arbitrary functions with potentially tainted input. Users should upgrade to version 5.2.2 or later to address this vulnerability (Debian Security, Snyk Blog).