NVD / CVE Program· CNA apache

CVE-2023-43622: Apache HTTP Server: DoS in HTTP/2 with initial windows size 0

Noroxi assessment

Priority: Plan (action score 51/100)

Public proof-of-concept code exists (GitHub); there is no record of exploitation in the wild.
Probability of exploitation in the next 30 days: 68.8% (FIRST EPSS); higher than 99.3% of all records.
Anyone who can reach it over the internet can trigger it. No account or password is required. No user action is required. No special conditions are required; it is repeatable.
According to CISA the attack is automatable: targets can be found by mass scanning.
Fixed version: Apache Software Foundation Apache HTTP Server 2.4.58.
Mentioned 1 time in Turkish national cyber security advisories (siberguvenlik.gov.tr).

Add it to your regular patch cycle. Upgrade to Apache Software Foundation Apache HTTP Server 2.4.58 or later.

Generated automatically from the record's data: CVSS (NVD and CNA), CISA KEV and SSVC, FIRST EPSS, exploit sources, fixed versions. How we calculate it

Primary sources: NVD · CVE.org · FIRST EPSS

An attacker, opening a HTTP/2 connection with an initial window size of 0, was able to block handling of that connection indefinitely in Apache HTTP Server. This could be used to exhaust worker resources in the server, similar to the well known "slow loris" attack pattern. This has been fixed in version 2.4.58, so that such connection are terminated properly after the configured connection timeout. This issue affects Apache HTTP Server: from 2.4.55 through 2.4.57. Users are recommended to upgrade to version 2.4.58, which fixes the issue.

HighCVSS 7.5 · v3.1—Proof of concept Fix available

Published: Oct 23, 2023
Updated: Jun 17, 2026
EPSS: 68.8% · 99th percentile
CWE: CWE-400

Report tools

JSON

Action score

Plan

Add it to your regular patch cycle.

CVSS: 30 / 40 · 7.5 / 10
CISA KEV: 0 / 30 · Not listed
EPSS: 21 / 30 · 68.8%

CISA SSVC decision

Exploitation: proof of concept
Automatable: yes
Technical impact: partial

Vulnrichment: CISA's decision-tree inputs.

Get told when this record changes

Not in KEV: no record of exploitation in the wild
Proof of concept exists, no weaponized module
A fix has been released

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Noroxi analysis

What does it mean in your environment?

The assessment above is generated automatically from the record's data; it doesn't know your environment. Our team verifies on your systems whether this vulnerability is actually exploitable and which mitigation is enough.

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Affected systems

Is your version affected?

Pick the product and type the version you run. It's compared with this record's version ranges in your browser; the version isn't sent anywhere.

Vendor	Product	CPE
apache	http server	cpe:2.3:a:apache:http_server

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Affected versions

NVD version ranges (for catalog products). Add the product to your stack with a version and matching uses these.

apache http server2.4.55 and later · before 2.4.58

Versions reported by the vendor

Affected version ranges reported by the assigning authority (apache). Independent of NVD's CPE analysis and usually ahead of it.

Apache Software Foundation Apache HTTP Server
- 2.4.55 and later · up to and including 2.4.57affected · semver

Package-level exposure

OSV and GitHub Advisory data: ecosystem, package and range. SBOM matching uses this table.

Ecosystem	Package	Affected range	Fix
AlmaLinux:9	mod_http2	before 2.0.26-1.el9	2.0.26-1.el9
Alpine:v3.15	apache2	before 2.4.58-r0	2.4.58-r0
Debian:11	apache2	before 2.4.59-1~deb11u1	2.4.59-1~deb11u1
Debian:12	apache2	before 2.4.59-1~deb12u1	2.4.59-1~deb12u1
Debian:13	apache2	before 2.4.58-1	2.4.58-1
openSUSE:Tumbleweed	apache2	before 2.4.58-1.1	2.4.58-1.1
Red Hat:enterprise_linux:9::appstream	mod_http2	before 0:2.0.26-1.el9	0:2.0.26-1.el9
Red Hat:enterprise_linux:9::appstream	mod_http2-debuginfo	before 0:2.0.26-1.el9	0:2.0.26-1.el9
Red Hat:enterprise_linux:9::appstream	mod_http2-debugsource	before 0:2.0.26-1.el9	0:2.0.26-1.el9

Same product

apache: all records

Other highest-scoring records for the same primary product.

CVE-2021-42013Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773)KEV
99Now
CVE-2021-41773Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49KEV
99Now
CVE-2024-38475Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path.KEV
96Now

Published before and after this one in the same product

← EarlierCVE-2023-27522Mar 7, 2023 · Apache HTTP Server: mod_proxy_uwsgi HTTP response splitting
31Monitor
← EarlierCVE-2023-31122Oct 23, 2023 · Apache HTTP Server: mod_macro buffer over-read
31Monitor
Later →CVE-2023-45802Oct 23, 2023 · Apache HTTP Server: HTTP/2 stream memory not reclaimed right away on RST
24Monitor

Remediation

Which version to upgrade to

Fix versions compiled from the vendor, package registries and Microsoft. Verify the vendor's note before upgrading.

Product / package	Fixed version	Source
Apache Software Foundation Apache HTTP Server	2.4.58 · description	Vendor (CNA)
almalinux:mod_http2	2.0.26-1.el9 · AlmaLinux:9	Package registry (OSV)
alpine:apache2	2.4.58-r0 · Alpine:v3.15	Package registry (OSV)
debian:apache2	2.4.59-1~deb12u1 · Debian:12	Package registry (OSV)
opensuse:apache2	2.4.58-1.1 · openSUSE:Tumbleweed	Package registry (OSV)
red hat:mod_http2	0:2.0.26-1.el9 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:mod_http2-debuginfo	0:2.0.26-1.el9 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)
red hat:mod_http2-debugsource	0:2.0.26-1.el9 · Red Hat:enterprise_linux:9::appstream	Package registry (OSV)

Exploit status

Proof of concept available

A public proof of concept or detection signature exists. Exploit knowledge is out there; don't delay patching.

Evidence

Proof-of-concept repository on GitHub ×1

Noroxi does not host or link to exploit code. Metasploit module names and Nuclei template ids are shown (names, not code); Exploit-DB entries and PoC repositories are given as counts only.

Public exploit evidence
Source	Kind	Date
Proof-of-concept repository on GitHub	stars:1	2024-05-29

Research context

For pentesters and researchers: attack profile, score disagreement, timeline, patch commits, credits, variant and chain candidates, bug bounty scope. All derived from existing data; no exploit code.

Timeline

From publication to today: proof of concept, Metasploit module, CISA KEV and fix record. Dates are as reported by the sources.

PublishedOct 23, 2023
First PoCMay 29, 2024+219 d
TodayNov 1, 2026+1105 d

EPSS, last 120 days

FIRST EPSS daily score; only changes of 0.01 or more are recorded (step chart).

Patch and commit links

Commit, PR and diff links among the references. A starting point for patch-diffing and variant hunting; fixes, not exploits.

No commit or PR link among the references.

Credits

All researchers

Finders, reporters and analysts named in the CNA record. Click a name for that researcher’s other records.

Choongin Lee (Korea University)finder
Isa Jafarov (City UniversityNew York)finder
Prof. Heejo Lee (Korea University)finder
Prof. Sven Dietrich (City UniversityNew York)finder

Variant candidates

Same product, same weakness class, within 18 months. If the patch missed the root cause, the sibling bug is here.

No nightly-computed relations.

Chain candidates

An authentication bypass and a privilege-requiring bug in the same product, published close together: combined they may become an unauthenticated path.

—

Bug bounty scope

No known public program.

Source: bounty-targets-data (public HackerOne, Bugcrowd, Intigriti, YesWeHack listings).

National notice (Türkiye Cybersecurity Directorate / USOM)

Official security notices citing this record; remediation advice is on the agency's page.

TR-23-0662 · Nov 27, 2023(Apache HTTP Sunucusu Güvenlik Zafiyeti)

All national notices →

Technical details

Attack conditions

Anyone who can reach it over the internet can trigger it.
No account or password is required.
No user action is required.
No special conditions are required; it is repeatable.

If successful

Confidentiality: none
Integrity: none
Availability: high · the service can be disrupted

Attack vector: Network
Attack complexity: Low
Privileges required: None
User interaction: None
Scope: Unchanged
Confidentiality impact: None
Integrity impact: None
Availability impact: High

Weakness class (CWE)

CWE-400 · Uncontrolled Resource Consumption

CVSS vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

nvd-primary

Root cause

Code that parses nested structures sets no depth or size limit. A small input can turn into a disproportionate processing load.

The bug in code

The whole CWE-400 class

A representative example of this vulnerability class. Not the vendor's source code; it shows the faulty pattern and its fix.

Vulnerable

1function expand(node) {
2  return node.children.map(expand);
3}

Fixed

1const MAX_DEPTH = 32;
2function expand(node, depth = 0) {
3  if (depth > MAX_DEPTH) throw new Error("too deep");
4  return node.children.map((c) => expand(c, depth + 1));
5}

Attack context

MITRE CAPEC attack patterns and ATT&CK techniques for this weakness class (CWE). A starting point for detection rules and threat hunting.

Attack patterns (CAPEC)

ATT&CK techniques

Endpoint Denial of ServiceT1499

Change log

Fix✗ → ✓Sep 28, 2026, 10:10 PM UTC

For records you follow, these changes also arrive as notifications. →

References

httpd.apache.org/security/vulnerabilities_24.html

Show all references (1 more)

security.netapp.com/advisory/ntap-20231027-0011/

Vendor advisories and official records. Exploit/PoC links are deliberately left out.

All records