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

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• 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.

From the GitHub advisory

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.

Weakness type: CWE-502.

Product: feast (PyPI) · Assigned by: VulnCheck · Published: 2026-06-24

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Attack requirements: none
• Privileges required: none (no login)
• User interaction: none

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• 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 2026-11-04): 1.41% probability of exploitation activity in the next 30 days; percentile 73.

Timeline

• 2026-06-24 — CVE record published by VulnCheck
• 2026-06-24 — GitHub-reviewed advisory GHSA-q63x-9pfm-mjx4 published (critical)
• 2026-08-28 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vendor and project advisories, patches

1. Release Notes github.com
2. Patch Commit github.com
3. access.redhat.com access.redhat.com

Vulnerability records

1. GitHub Advisory GHSA-q63x-9pfm-mjx4 github.com
2. CVE.org record CVE-2026-56121 cve.org
3. NVD entry CVE-2026-56121 nvd.nist.gov

Other references from the CVE record and advisory

1. Huntr Disclosure huntr.com
2. vulncheck.com vulncheck.com
3. access.redhat.com access.redhat.com
4. RHBZ#2492229 bugzilla.redhat.com
5. security.access.redhat.com security.access.redhat.com

Critical PyPI advisories · Today’s Security Digest