CVE-2021-3121: An issue was discovered in GoGo Protobuf before 1.3.2

This month

HIGH 8.6REMOTEUPGRADEUPGRADE

CVE-2021-3121 is a high-severity flaw (CVSS 8.6) affecting protobuf, consul. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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.

Why this priority

High severity
Remotely exploitable, no login, no user action

A fixed release or distro patch exists.

Risk facts

CVSS score	8.6 (High)
Attack vector	Network (remote)
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	3.4% (top 11%)
CISA exploited list	No
Weakness	CWE-129
Published	2021-01-11
Last modified	2026-06-17

Publisher (CNA): MITRE · Vendor: golang · hashicorp

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2021-01-11 06:15 UTCPublished CVE record published
2026-06-17 04:04 UTCUpdated Record last modified

golang protobuf UPGRADE

Affected: < 1.3.2

Fixed in: 1.3.2

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy protobuf || rpm -q protobuf || protobuf --version

2. UPGRADE to 1.3.2 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade protobuf

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade protobuf

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

hashicorp consul UPGRADE

Affected: < 1.8.15 · >= 1.9.0 and < 1.9.9 · >= 1.10.0 and < 1.10.2

Fixed in: 1.8.15, 1.9.9, 1.10.2

Safe to downgrade to: a release before 1.9.0

1. Check installed version

apt-cache policy consul || rpm -q consul || consul --version

2. UPGRADE to 1.8.15 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade consul

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade consul

Note

Distros often backport fixes without changing the version number. Confirm with the distro advisory or changelog.

3. If no update is available yet, DOWNGRADE to a release before 1.9.0 (Debian / Ubuntu)

apt-cache madison consul sudo apt install consul=<VERSION_BEFORE_1.9.0> sudo apt-mark hold consul

3. If no update is available yet, DOWNGRADE (RHEL / Amazon Linux / Fedora)

dnf --showduplicates list consul sudo dnf downgrade consul-<VERSION_BEFORE_1.9.0> sudo dnf versionlock add consul

Downgrade risk

Downgrading can break dependent software and may reopen older bugs. Read the distro advisory first and test on a non-production host.

After downgrade

Restart the service, and keep the package held until a fixed release ships.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2021-3121?

protobuf: upgrade to 1.3.2; consul: upgrade to 1.8.15, 1.9.9, 1.10.2. Exact commands for each OS are on this page.

Is CVE-2021-3121 being exploited?

CVE-2021-3121 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2021-3121 affect?

CVE-2021-3121 affects protobuf, consul. Severity is high (CVSS 8.6). 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.

How urgent is CVE-2021-3121?

Priority 57/100. High severity; Remotely exploitable, no login, no user action

Software pages

Go (Golang) vulnerabilities · Consul vulnerabilities

Related CVEs

CVE-2026-0994 HIGH 7.5 UPGRADE A denial-of-service (DoS) vulnerability exists in google.protobuf.json_format.ParseDict() in Python, where the
CVE-2024-7254 HIGH 7.5 UPGRADE UPGRADE Any project that parses untrusted Protocol Buffers data containing an arbitrary number of nested groups / seri
CVE-2024-2410 HIGH 7.6 UPGRADE The JsonToBinaryStream() function is part of the protocol buffers C++ implementation and is used to parse JSON
CVE-2023-24535 HIGH 7.5 DOWNGRADE Parsing invalid messages can panic
CVE-2021-22570 MEDIUM 6.5 UPGRADE MITIGATE Nullptr dereference when a null char is present in a proto symbol

References

← Back to latest CVEs