CVE-2026-23918Public exploitNetwork attack vector

Pre-auth code execution via duplicate HTTP/2 cleanup

Published May 4, 2026 · Updated May 4, 2026

Double free in mod_http2 in Apache HTTP Server 2.4.66 allows remote attackers to crash workers or execute code via an early stream reset. A HEADERS frame followed immediately by RST_STREAM makes two nghttp2 callbacks add the same h2_stream pointer to m->spurge, so cleanup destroys its APR pool twice. The crash path requires an enabled HTTP/2 endpoint and a multithreaded event or worker MPM; the demonstrated code-execution chain also requires an address leak, the APR mmap allocator, and mod_status.

CVSS severity8.8
High
EPSS probability49.73%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Double free in mod_http2 in Apache HTTP Server 2.4.66 allows remote attackers to crash workers or execute code via an early stream reset. A HEADERS frame followed immediately by RST_STREAM makes two nghttp2 callbacks add the same h2_stream pointer to m->spurge, so cleanup destroys its APR pool twice. The crash path requires an enabled HTTP/2 endpoint and a multithreaded event or worker MPM; the demonstrated code-execution chain also requires an address leak, the APR mmap allocator, and mod_status.

The record

CVE
CVE-2026-23918
Published
May 4, 2026
Updated
May 4, 2026
Vendor
The Apache Software Foundation
Product
Apache HTTP Server
Classifications
CWE-415, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 4, 2026CVE publishedPublication date reported by the CVE source.
  2. May 4, 2026Record 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=2.4.66

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

The Apache Software Foundation · Apache HTTP Serverversion=2.4.66

Published CVSS scores

8.8CISA-ADPCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
8.8redhat-SADPCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/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
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-415Double Free
T1190Exploit Public-Facing Application

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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