---
title: "CVE-2026-56121: Feast vulnerable to unsafe deserialization RCE in registry server via UDF proto"
url: https://erroneo.us/security/cve/CVE-2026-56121/
description: "CVE-2026-56121 (feast (PyPI)): Feast before 0.63.0 contains an unsafe deserialization vulnerability that allows unauthenticated or unauthorized attackers to…"
type: vulnerability-record
section: "Security Digest"
date_published: 2026-06-24
date_modified: 2026-11-03
publisher: erroneo.us
author: erroneo.us Security Desk
cve: "CVE-2026-56121"
kev: false
cvss: 9.3
epss: 0.01406
license: All rights reserved. Quote with attribution and a link.
---

# CVE-2026-56121: Feast vulnerable to unsafe deserialization RCE in registry server via UDF proto

**Signal:** Critical and remotely reachable. No known exploitation yet, but it is network-reachable without credentials. (Computed from CISA KEV, EPSS and CVSS; not an editorial verdict.)

## Should you act?

- Not in CISA KEV , but CISA’s SSVC assessment records a public proof-of-concept, so attack code exists.
- EPSS 1.4% , percentile 73: FIRST’s model estimates a 1.4% chance of exploitation activity in the next 30 days, higher than 73% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
- Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
- Only applies if your dependency tree includes feast (PyPI) < 0.63.0, fixed in 0.63.0 . Check your lockfile, including transitive dependencies.

## What it is

Feast before 0.63.0 contains an unsafe deserialization vulnerability that allows unauthenticated or unauthorized attackers to achieve remote code execution by sending a crafted gRPC request to the registry server. The userdefinedfunction.body field of an OnDemandFeatureView spec is decoded from base64 and passed to dill.loads() before any authorization check is performed, enabling attackers to embed a malicious serialized Python object with an arbitrary reduce method to execute OS commands as the feast service account.

## Affected packages

- PyPI `feast` < 0.63.0 → fixed: 0.63.0

## Affected products (CVE record)

- feast-dev feast: < 0.63.0

## Severity

- VulnCheck CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`
- VulnCheck CVSS 3.1: 9.8 `CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- redhat-SADP CVSS 3.1: 8.8 `CVSS:3.1/AV:A/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`
- GitHub CVSS 4.0: 9.3 `CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N`

## Exploitation

- CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
- CISA SSVC assessment: exploitation poc , automatable yes , technical impact total .
- FIRST EPSS (model of 2026-11-05): 1.41% probability of exploitation activity in the next 30 days; percentile 73.

## Sources

- [Release Notes](https://github.com/feast-dev/feast/releases/tag/v0.63.0)
- [Patch Commit](https://github.com/feast-dev/feast/commit/835cda8e2c1359f1f496ad72701dbd6a73bdb25a)
- [access.redhat.com](https://access.redhat.com/errata/RHSA-2026:60520)
- [GitHub Advisory GHSA-q63x-9pfm-mjx4](https://github.com/advisories/GHSA-q63x-9pfm-mjx4)
- [CVE.org record CVE-2026-56121](https://www.cve.org/CVERecord?id=CVE-2026-56121)
- [NVD entry CVE-2026-56121](https://nvd.nist.gov/vuln/detail/CVE-2026-56121)
- [Huntr Disclosure](https://huntr.com/bounties/d64b8111-180b-46ba-afa3-c877fda2ede6)
- [vulncheck.com](https://www.vulncheck.com/advisories/feast-unauthenticated-rce-via-applyfeatureview-grpc-deserialization)
- [access.redhat.com](https://access.redhat.com/security/cve/CVE-2026-56121)
- [RHBZ#2492229](https://bugzilla.redhat.com/show_bug.cgi?id=2492229)
- [security.access.redhat.com](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-56121.json)

---
Source page: https://erroneo.us/security/cve/CVE-2026-56121/ · Security Digest: https://erroneo.us/security/ · More: https://erroneo.us/llms.txt