CVE-2023-0056Network attack vector

Service crash via malformed HTTP/2 interim response

Published Mar 23, 2023 · Updated Feb 25, 2025

Uncontrolled resource consumption in HAProxy 2.2.19, 2.2.24, and 2.2.26 allows remote authenticated users to crash the proxy. The HTTP/2 multiplexer accepts an informational response whose HEADERS frame sets END_STREAM, leaving an unexpected end-of-message block; http_wait_for_response then dereferences a NULL start-line pointer. Reachability requires control of a malicious backend server used by HAProxy, and exploitation terminates the proxy process, interrupting availability.

CVSS severity6.5
Medium
EPSS probability1.83%
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 HAProxy 2.2.19, 2.2.24, and 2.2.26 allows remote authenticated users to crash the proxy. The HTTP/2 multiplexer accepts an informational response whose HEADERS frame sets END_STREAM, leaving an unexpected end-of-message block; http_wait_for_response then dereferences a NULL start-line pointer. Reachability requires control of a malicious backend server used by HAProxy, and exploitation terminates the proxy process, interrupting availability.

The record

CVE
CVE-2023-0056
Published
Mar 23, 2023
Updated
Feb 25, 2025
Vendor
HAProxy Technologies
Product
HAProxy
Classifications
CWE-400, T1499
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. Mar 23, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 25, 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=unknown

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

HAProxy Technologies · HAProxyversion=unknown

Published CVSS scores

6.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
6.5NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-400Uncontrolled Resource Consumption
T1499Endpoint Denial of Service

Public exploit references

No public exploit references are available in this record.

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Technologies

Your stack

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Your stack

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