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

Severity: medium (CVSS 4.9 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 1.9% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2021-03-08 · updated 2026-06-17

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.

Affected products

Fedoraproject Fedora: 33, 34
github.com/pires/go-proxyproto: before 0.5.0 — fixed in 0.5.0

How to fix

Upgrade to a fixed version: github.com/pires/go-proxyproto 0.5.0. Check the vendor advisory for mitigations.

References

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