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HIGH severity

CVE-2021-23409 — go-proxyproto

HIGHFix: pires/go-proxyproto#74

CVE-2021-23409 is a high-severity (CVSS 7.5) vulnerability in github.com/pires/go-proxyproto. A fix is available for github.com/pires/go-proxyproto — see the affected versions and patch details below.

github.com/pires/go-proxyproto vulnerable to DoS via Connection descriptor exhaustion

Also known asGHSA-xcf7-q56x-78ghGO-2022-0233
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Oct 10, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
1.6%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs76th percentile — riskier than 76% of all scored CVEsHighest risk
0.41%0.99%1.57%2.15%0.9%1.6%Apr 26Aug 26Oct 26

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

How urgent is this, really

CVE-2021-23409 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,386 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

1 pkg affected
🐹github.com/pires/go-proxyproto

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

The package github.com/pires/go-proxyproto before 0.6.1 is vulnerable to Denial of Service (DoS) via creating connections without the proxy protocol header. While this issue was patched in 0.6.0, the fix introduced additional issues which were subsequently patched in 0.6.1.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/pires/go-proxyprotoall versions0.6.1go get github.com/pires/go-proxyproto@v0.6.1

Affected Products

1 product · 1 configurations
Application
go-proxyprotogo-proxyproto_project
< 0.6.0
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update github.com/pires/go-proxyproto to 0.6.1 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23409 is resolved across your whole dependency graph.

  3. Workarounds

    Cap what an attacker can consume: apply request size, rate and timeout limits in front of the affected component, and run it with memory and CPU limits so exhaustion degrades one worker rather than the whole service.

Frequently Asked Questions

The package `github.com/pires/go-proxyproto` before 0.6.1 is vulnerable to Denial of Service (DoS) via creating connections without the proxy protocol header. While this issue was patched in 0.6.0, the fix introduced additional issues which were subsequently patched in 0.6.1.
O3 Security · Impact-Aware SCA

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CVE-2021-23409: go-proxyproto DoS — Fixed in 0.6.1