# CVE-2026-56121: Feast unsafe deserialization in registry server gRPC interface

Source: https://junglewise.ai/threats/cve-2026-56121-feast-unsafe-deserialization-in-registry-server-grpc-interface  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-56121 · Severity: critical · CVSS 9.8 · Published 2026-06-24

Feast, an open-source feature store used for machine learning, is vulnerable to a critical security flaw in its registry server. An unauthenticated attacker can send a specially crafted network request that forces the system to execute malicious code. This could allow an attacker to take full control of the server, access sensitive machine learning data, or disrupt operations.

Technologies: [feast (PyPI)](https://junglewise.ai/threats/technologies/pypi-feast). Vendors: [PyPI](https://junglewise.ai/threats/vendors/pypi).

## Quick answers

**Is CVE-2026-56121 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-56121 being exploited in the wild.

**How severe is CVE-2026-56121?** Critical severity, with a CVSS score of 9.8, published 24 June 2026.

**Which products and versions are affected?** Feast Dev Feast < 0.63.0; feast (PyPI) < 0.63.0, ECOSYSTEM:introduced=0,fixed=0.63.0.

**Is there a fix for CVE-2026-56121?** Yes. feast (PyPI): upgrade to 0.63.0 or later. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-56121 attacked?** It is attacked over the network, in a software library.

**Am I affected by CVE-2026-56121?** Check whether you run Feast Dev Feast or feast (PyPI) at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- feast (PyPI): upgrade to 0.63.0 or later

  ```sh
  pip install "feast>=0.63.0"
  ```


## Technical details

An unsafe deserialization vulnerability exists in Feast's registry server due to the use of 'dill.loads()' on untrusted input. Specifically, the 'user_defined_function.body' field within an 'OnDemandFeatureView' specification is decoded from base64 and deserialized before any authorization checks are performed. A remote, unauthenticated attacker can exploit this by sending a crafted gRPC request containing a malicious Python object with a custom '__reduce__' method. Successful exploitation allows for arbitrary OS command execution under the context of the Feast service account. This issue is resolved in version 0.63.0.

## Affected products

- Feast Dev Feast < 0.63.0

## Identifiers

- CVE-2026-56121
- GHSA-q63x-9pfm-mjx4

## Timeline

- 2026-04-22: patched: Fix commit 835cda8 merged into master
- 2026-05-04: advisory: Version 0.63.0 released
- 2026-06-24: disclosed: CVE published and NVD record created

## References

- [https://github.com/feast-dev/feast/commit/835cda8e2c1359f1f496ad72701dbd6a73bdb25a](https://github.com/feast-dev/feast/commit/835cda8e2c1359f1f496ad72701dbd6a73bdb25a)
- [https://github.com/feast-dev/feast/releases/tag/v0.63.0](https://github.com/feast-dev/feast/releases/tag/v0.63.0)
- [https://huntr.com/bounties/d64b8111-180b-46ba-afa3-c877fda2ede6](https://huntr.com/bounties/d64b8111-180b-46ba-afa3-c877fda2ede6)
- [https://www.vulncheck.com/advisories/feast-unauthenticated-rce-via-applyfeatureview-grpc-deserialization](https://www.vulncheck.com/advisories/feast-unauthenticated-rce-via-applyfeatureview-grpc-deserialization)

## Related threats

- [Feast vulnerable to arbitrary code execution via unsafe deserialization of dill-serialized UDFs](https://junglewise.ai/threats/cve-2026-18948-a-flaw-was-found-in-feast-the-system-improperly-deserializes-user)
- [PYSEC-2026-1367 - Feast Cross-Origin Resource Sharing vulnerability](https://junglewise.ai/threats/cve-2024-11602-feast-cross-origin-resource-sharing-vulnerability)
- [Feast remote code execution in Kubernetes materializer job](https://junglewise.ai/threats/cve-2025-11157-feast-remote-code-execution-in-kubernetes-materializer-job)