CVE-2025-53020Public exploitNetwork attack vector

Remote service interruption via HPACK header duplication

Published Jul 10, 2025 · Updated Nov 4, 2025

Memory exhaustion in Apache HTTP Server 2.4.17 through 2.4.63 allows remote attackers to interrupt service via HTTP/2 requests. HTTP/2 header processing duplicates repeated attacker-controlled header names into request-lifetime memory instead of reusing the HPACK dynamic-table entry. An unauthenticated client with HTTP/2 access can repeat large indexed header names across requests until httpd exhausts available memory and becomes unavailable.

CVSS severity7.5
High
EPSS probability4.80%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Memory exhaustion in Apache HTTP Server 2.4.17 through 2.4.63 allows remote attackers to interrupt service via HTTP/2 requests. HTTP/2 header processing duplicates repeated attacker-controlled header names into request-lifetime memory instead of reusing the HPACK dynamic-table entry. An unauthenticated client with HTTP/2 access can repeat large indexed header names across requests until httpd exhausts available memory and becomes unavailable.

The record

CVE
CVE-2025-53020
Published
Jul 10, 2025
Updated
Nov 4, 2025
Vendor
The Apache Software Foundation
Product
Apache HTTP Server
Classifications
CWE-401, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 10, 2025CVE publishedPublication date reported by the CVE source.
  2. Nov 4, 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=2.4.17 <=2.4.63

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache HTTP Serverversion=2.4.17 <=2.4.63

Published CVSS scores

7.5CISA-ADPCVSS:3.1/AV:N/AC:L/PR:N/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.

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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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-401Missing Release of Memory after Effective Lifetime
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

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Technologies

Your stack

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Your stack

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