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High, CVSS 8.6

Improper Input Validation in GoGo Protobuf

CVE-2021-3121GHSA-c3h9-896r-86jm

What to do

Vendor fix available. Upgrade each affected package to the fixed version on its release line (github.com/gogo/protobuf 1.3.2), redeploy, then verify what is actually installed.

This page has no inventory attached, so it cannot say whether you are affected. A vendor fix is not proof that your deployment is fixed.

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Affected packages

Sources

Severity and exploitation
Exploitation
No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.
CVSS
8.6 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:L/A:H
EPSS
  • CVE-2021-3121: 3.43% estimated exploitation activity in the next 30 days; percentile 88.94 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.
Source description

As published by the source; long descriptions are shortened.

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.

Dates and revisions
Published by the source
Last modified by the source
Source last checked
  1. Revision 1 · created ·

    Published from ghsa record GHSA-c3h9-896r-86jm

Agent brief

Preview the exact text before you copy it. Commands are read-only suggestions; review them before running anything.

# Patch Next advisory brief: CVE-2021-3121

Advisory: Improper Input Validation in GoGo Protobuf
IDs: CVE-2021-3121, GHSA-c3h9-896r-86jm
Record: https://patchnext.com/advisories/cve-2021-3121 (revision 1, source checked 26 Oct 2026, 14:55 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 8.6)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Vendor fix available; fixed versions by package: github.com/gogo/protobuf 1.3.2. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/gogo/protobuf: affected < 1.3.2; fixed in 1.3.2

## Suggested inspection (read-only)
- Go github.com/gogo/protobuf: check the installed version with your package manager.

## Supported action
Upgrade each affected component to a fixed version on its release line. For a transitive dependency, upgrade the parent package or add an override or constraint, then regenerate the lockfile. Redeploy every environment that ran an affected version.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/gogo/protobuf.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-c3h9-896r-86jm (GitHub-reviewed advisory GHSA-c3h9-896r-86jm lists affected ranges: Go github.com/gogo/protobuf >=0 <1.3.2)

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