CVE-2021-23351: The package github.com/pires/go-proxyproto before 0.5.0 are vulnerable to Denial of Service (DoS) via the pars

Q: How do I fix CVE-2021-23351?

go-proxyproto: upgrade to 0.5.0; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Q: Is CVE-2021-23351 being exploited?

CVE-2021-23351 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

Q: What does CVE-2021-23351 affect?

CVE-2021-23351 affects go-proxyproto, fedora. Severity is medium (CVSS 4.4). The package github.com/pires/go-proxyproto before 0.5.0 are vulnerable to Denial of Service (DoS) via the parseVersion1() function. The reader in this package is a default bufio.Reader wrapping a net.Conn. It will read from the connection u

Q: How urgent is CVE-2021-23351?

Priority 35/100. No elevated risk signals yet.

Routine

MEDIUM 4.4UPGRADEMITIGATE

CVE-2021-23351 is a medium-severity flaw (CVSS 4.4) affecting go-proxyproto, fedora. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

The package github.com/pires/go-proxyproto before 0.5.0 are vulnerable to Denial of Service (DoS) via the parseVersion1() function. The reader in this package is a default bufio.Reader wrapping a net.Conn. It will read from the connection until it finds a newline. Since no limits are implemented in the code, a deliberately malformed V1 header could be used to exhaust memory in a server process using this code - and create a DoS. This can be explo

Why this priority

No elevated risk signals yet

A fixed release or distro patch exists.

Risk facts

CVSS score	4.4 (Medium)
Attack vector	Network (remote)
Attack complexity	High
Privileges needed	High
User interaction	None
EPSS exploit chance	1.9% (top 21%)
CISA exploited list	No
Published	2021-03-08
Last modified	2026-06-17

Publisher (CNA): Snyk · Vendor: fedoraproject · go-proxyproto project

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

Am I affected?

Timeline

2021-03-08 05:15 UTCPublished CVE record published
2026-06-17 03:38 UTCUpdated Record last modified

go-proxyproto project go-proxyproto UPGRADE

Affected: < 0.5.0

Fixed in: 0.5.0

Safe to downgrade to: no unaffected older release

1. Check installed version

apt-cache policy go-proxyproto || rpm -q go-proxyproto || go-proxyproto --version

2. UPGRADE to 0.5.0 (Debian / Ubuntu)

sudo apt update && sudo apt install --only-upgrade go-proxyproto

2. UPGRADE (RHEL / Amazon Linux / Fedora)

sudo dnf upgrade go-proxyproto

Note

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

fedoraproject fedora MITIGATE

Affected: 33 · 34

Fixed in: no fixed release known

Safe to downgrade to: a release before 33

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

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-2021-23351?

go-proxyproto: upgrade to 0.5.0; fedora: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2021-23351 being exploited?

CVE-2021-23351 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-2021-23351 affect?

CVE-2021-23351 affects go-proxyproto, fedora. Severity is medium (CVSS 4.4). The package github.com/pires/go-proxyproto before 0.5.0 are vulnerable to Denial of Service (DoS) via the parseVersion1() function. The reader in this package is a default bufio.Reader wrapping a net.Conn. It will read from the connection u

How urgent is CVE-2021-23351?

Priority 35/100. No elevated risk signals yet.

Software pages

GitHub vulnerabilities

Related CVEs

CVE-2021-23409 HIGH 7.5 UPGRADE The package github.com/pires/go-proxyproto before 0.6.0 are vulnerable to Denial of Service (DoS) via creating

References

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