How severe is CVE-2021-3121?

CVE-2021-3121 has a CVSS score of 8.6/10, rated HIGH. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-3121?

CVE-2021-3121 affects the following packages: github.com/gogo/protobuf (Go). Ecosystems affected: Go.

How do I fix CVE-2021-3121?

Update github.com/gogo/protobuf to 1.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3121 is resolved across your whole dependency graph.

How do I detect CVE-2021-3121 in my Go dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gogo/protobuf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2021-3121 if there is no patch (or I can't update yet)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Is CVE-2021-3121 actively exploited in the wild?

No public exploit code has been indexed for CVE-2021-3121 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2021-3121?

CVE-2021-3121 has an EPSS (Exploit Prediction Scoring System) score of 3.4%, placing it in the 89th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2021-3121?

CVE-2021-3121 is classified as CWE-129 (CWE-129). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2021-3121 published, and has it been updated?

CVE-2021-3121 was published on January 11, 2021 and was last updated on October 24, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐹

🐹 Go

Not in CISA KEV

HIGH severity

CVE-2021-3121 — protobuf

HIGHFix: gogo/protobuf@b03c65e

CVE-2021-3121 is a high-severity (CVSS 8.6) CWE-129 vulnerability in github.com/gogo/protobuf. A fix is available for github.com/gogo/protobuf — see the affected versions and patch details below.

Improper Input Validation in GoGo Protobuf

Also known asBIT-consul-2021-3121BIT-protobuf-2021-3121GHSA-c3h9-896r-86jmGO-2021-0053

Published

Jan 11, 2021

Updated

Oct 24, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 8, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

3.4%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs89th percentile — riskier than 89% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected

🐹github.com/gogo/protobuf

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

An issue was discovered in GoGo Protobuf before 1.3.2. plugin/unmarshal/unmarshal.go lacks certain index validation, aka the "skippy peanut butter" issue.

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐹Go	`github.com/gogo/protobuf`	all versions	1.3.2`go get github.com/gogo/protobuf@v1.3.2`

Affected Products

2 products · 7 configurations

Application

protobufgolang

< 1.3.2

range

Application

consulhashicorp

≥ 1.10.0 && < 1.10.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/gogo/protobuf, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update github.com/gogo/protobuf to 1.3.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-3121 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

OpenShift Container Platform (OCP), OpenShift ServiceMesh (OSSM) and Red Hat OpenShift Jaeger (RHOSJ) all include code generated by github.com/gogo/protobuf to parse protobuf messages. However, no component is known to accept protobuf messages from unauthenticated sources, hence this vulnerability is rated Moderate…

Product	Fixed in	Advisory
AMQ Broker 7.10.1	`amq-broker-operator-container`	RHSA-2022:6916
Cryostat 2 on RHEL 8	`cryostat-20-tech-preview/cryostat-grafana-dashboard-rhel8:2.1.0-1`	RHSA-2022:1679
OpenShift Logging 5.0	`openshift-logging/cluster-logging-rhel8-operator:v5.0.4-5`	RHSA-2021:2136
OpenShift Logging 5.0	`openshift-logging/elasticsearch-proxy-rhel8:v5.0.5-5`	RHSA-2021:2374
OpenShift Service Mesh 2.0	`kiali-0:v1.24.7.redhat1-1.el8`	RHSA-2022:1276
Red Hat Advanced Cluster Management for Kubernetes 2.0 for RHEL 8	`rhacm2/acm-operator-bundle:v2.0.8-7`	RHSA-2021:0719
Red Hat Advanced Cluster Management for Kubernetes 2.1 for RHEL 8	`rhacm2/acm-must-gather-rhel8:v2.1.3-3`	RHSA-2021:0607
Red Hat OpenShift Container Platform 4.10	`openshift4/ose-csi-driver-manila-rhel8-operator:v4.10.0-202202160023.p0.g16f67d6.assembly.stream`	RHSA-2022:0056

Frequently Asked Questions

An issue was discovered in GoGo Protobuf before 1.3.2. plugin/unmarshal/unmarshal.go lacks certain index validation, aka the "skippy peanut butter" issue.

O3 Security · Impact-Aware SCA

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