# CVE-2026-56121: Feast < 0.63.0 Unauthenticated RCE via ApplyFeatureView gRPC Deserialization

> Unauthenticated attackers can execute arbitrary code on Feast registry servers via unsafe deserialization in gRPC requests.

- **Severity:** Critical 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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 24 Jun 2026
- **Updated:** 28 Aug 2026
- **Also known as:** GHSA-q63x-9pfm-mjx4

## What is CVE-2026-56121?

CVE-2026-56121 is a critical unsafe deserialization vulnerability in feast-dev feast, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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 user_defined_function.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.

Weakness: CWE-502 (Deserialization of Untrusted Data)

## Which versions are affected by CVE-2026-56121?


## How do I fix CVE-2026-56121?

No fix has been published for CVE-2026-56121 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-56121 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56121 exists.

Public exploit code:

- https://github.com/0xdak/CVE-2026-56121_exploit (github_poc): https://github.com/0xdak/CVE-2026-56121_exploit
- CVE-2026-56121 — Feast <0.63.0 unauthenticated RCE via gRPC registry dill.loads of OnDemandFeatureView UDF (pre-auth). Lab + PoC, verified e2e. (github_poc): https://github.com/BiiTts/CVE-2026-56121-Feast-Unauth-RCE
- https://github.com/joaovicdev/EXPLOIT-CVE-2026-56121 (github_poc): https://github.com/joaovicdev/EXPLOIT-CVE-2026-56121

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-56121 and fix it if it is affected.

What it is: CVE-2026-56121 is a critical unsafe deserialization vulnerability in feast-dev feast, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-56121 exists.

Affected product: feast-dev feast. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-56121/ (Markdown: https://insights.sbomify.com/CVE-2026-56121/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-56121
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-56121
- OSV: https://osv.dev/vulnerability/CVE-2026-56121

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-56121/
Summaries are generated and may contain mistakes; the official description above is the record.