CVE-2021-23351Public exploitNetwork attack vector

Service interruption via unbounded PROXY header read

Published Mar 8, 2021 · Updated Sep 17, 2024

Uncontrolled resource consumption in Pires go-proxyproto before 0.5.0 allows remote authenticated users to exhaust server memory. parseVersion1 reads a PROXY V1 header with bufio.Reader.ReadString until a newline, without enforcing the protocol's 107-byte maximum. The sender must be permitted to supply PROXY headers; an unterminated stream can consume memory until the hosting server stops acknowledging traffic.

CVSS severity4.4
Medium
EPSS probability1.87%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Uncontrolled resource consumption in Pires go-proxyproto before 0.5.0 allows remote authenticated users to exhaust server memory. parseVersion1 reads a PROXY V1 header with bufio.Reader.ReadString until a newline, without enforcing the protocol's 107-byte maximum. The sender must be permitted to supply PROXY headers; an unterminated stream can consume memory until the hosting server stops acknowledging traffic.

The record

CVE
CVE-2021-23351
Published
Mar 8, 2021
Updated
Sep 17, 2024
Vendor
Pires
Product
go-proxyproto
Classifications
CWE-400, T1499.003
Attack vector
network
Privileges
admin

Timeline

How it unfolded

  1. Mar 8, 2021CVE publishedPublication date reported by the CVE source.
  2. Sep 17, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=unspecified <0.5.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesadmin

What is affected?

Pires · go-proxyprotoversion=unspecified <0.5.0

Published CVSS scores

4.9NIST NVDCVSS:3.1/AV:N/AC:L/PR:H/UI:N/S:U/C:N/I:N/A:H
4.4SnykCVSS:3.1/AV:N/AC:H/PR:H/UI:N/S:U/C:N/I:N/A:H
4.0NIST NVDAV:N/AC:L/Au:S/C:N/I:N/A:P

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesadmin
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499.003Application Exhaustion Flood

Public exploit references

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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