CVE-2023-0836Network attack vector

Memory disclosure via uninitialized FastCGI record bytes

Published Mar 29, 2023 · Updated Feb 18, 2025

Information disclosure in affected HAProxy 2.1 through 2.7 releases allows remote attackers to expose memory to configured FastCGI backends. The FCGI_BEGIN_REQUEST encoder leaves five connection-buffer bytes uninitialized and transmits residual process data in each record. Exposure requires a configured FastCGI backend; the disclosed bytes can contain sensitive data, with no reported integrity or availability impact.

CVSS severity7.5
High
EPSS probability1.20%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Information disclosure in affected HAProxy 2.1 through 2.7 releases allows remote attackers to expose memory to configured FastCGI backends. The FCGI_BEGIN_REQUEST encoder leaves five connection-buffer bytes uninitialized and transmits residual process data in each record. Exposure requires a configured FastCGI backend; the disclosed bytes can contain sensitive data, with no reported integrity or availability impact.

The record

CVE
CVE-2023-0836
Published
Mar 29, 2023
Updated
Feb 18, 2025
Vendor
HAProxy Technologies
Product
HAProxy
Classifications
CWE-200, CWE-459, T1005
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Mar 29, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 18, 2025Record 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=HAProxy 2.8, HAProxy 2.7.1, HAProxy 2.6.8, HAProxy 2.5.11, HAProxy 2.4.21, HAProxy 2.2.27

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

HAProxy Technologies · HAProxyversion=HAProxy 2.8, HAProxy 2.7.1, HAProxy 2.6.8, HAProxy 2.5.11, HAProxy 2.4.21, HAProxy 2.2.27

Published CVSS scores

7.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N
3.7Amazon LinuxCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-200Exposure of Sensitive Information to an Unauthorized Actor
CWE-459Incomplete Cleanup
T1005Data from Local System

Public exploit references

No public exploit references are available in this record.

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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