---
id: CVE-2021-23351
aliases:
  - GHSA-fqh4-rh59-xhvf
  - SNYK-GOLANG-GITHUBCOMPIRESGOPROXYPROTO-1081577
title: github.com/pires/go-proxyproto denial of service vulnerability
summary: github.com/pires/go-proxyproto denial of service vulnerability
severity: medium
cvss: 4.9
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H'
vendor: pires
product: github.com/pires/go-proxyproto
ecosystem: go
affected:
  - github.com/pires/go-proxyproto < 0.5.0
patched:
  - github.com/pires/go-proxyproto 0.5.0
published: '2021-05-18'
updated: '2026-07-08'
source: OSV
sourceUrl: 'https://osv.dev/vulnerability/GHSA-fqh4-rh59-xhvf'
references:
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2021-23351'
  - url: 'https://github.com/pires/go-proxyproto/issues/69'
  - url: 'https://github.com/pires/go-proxyproto/pull/71'
  - url: >-
      https://github.com/pires/go-proxyproto/commit/7f48261db810703d173f27f3309a808cc2b49b8b
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/4BNVGJMVI3ZTZ675EFPUHPGXCKCGSX46
  - url: >-
      https://lists.fedoraproject.org/archives/list/package-announce@lists.fedoraproject.org/message/C36IBVOZXRTWM7MGTRUTOM56P5RR74VU
  - url: 'https://snyk.io/vuln/SNYK-GOLANG-GITHUBCOMPIRESGOPROXYPROTO-1081577'
tags:
  - osv
  - go
epss: 0.01871
epssPercentile: 0.78476
ingestedAt: '2026-07-09T18:56:36.354Z'
---

## Overview

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 exploited by sending a stream starting with PROXY and continuing to send data (which does not contain a newline) until the target stops acknowledging. The risk here is small, because only trusted sources should be allowed to send proxy protocol headers.

## Affected packages

- `github.com/pires/go-proxyproto < 0.5.0`

## Remediation

Upgrade to a patched release:

- `github.com/pires/go-proxyproto 0.5.0`