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TI-2023-23350 Aliases CVE-2023-43622GHSA-w2qc-22jv-44g8

Apache HTTP Server: DoS in HTTP/2 with initial windows size 0

Priority HIGH 76CWE-400Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
Denial of service
Confidentiality · integrity · availability
None · None · High
Fix status
Fixed

Attack profile from CVSS 3.1 · NVD. Fix status from CNA and Red Hat. Impact type from CWE-400.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.68818 99th percentileScored 2026-11-07
Fix Fixed Red Hat: 1 advisory

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
Yes
Technical impact
Partial

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
ApacheApache HTTP Server2.4.55 – 2.4.57—No fix listedCNA
  • Apache HTTP Server VendorApache Affected 2.4.55 – 2.4.57 Fixed in — No fix listed CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*2.4.55 to before 2.4.58VulnerableApache
  • cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:* Versions 2.4.55 to before 2.4.58 Vulnerable ·Apache

Remediation

Red Hat 1 advisory

  • RHSA-2024:2368 Released 2024-04-30 · Red Hat rating Moderate
    mod_http2 security update
    • Red Hat Enterprise Linux AppStream (v. 9) mod_http2-2.0.26-1.el9

Vendor assessments

Red Hat

Red Hat rating: Moderate. Red Hat's page for this CVE →

ProductStatusPlan or fix
Red Hat Enterprise Linux AppStream (v. 9)Fixed RHSA-2024:2368
Not affected: 2 products
  • Red Hat Enterprise Linux 8
  • Red Hat JBoss Core Services

Timeline

  1. 2026-10-02 Threatist record created from CVE-2023-43622
  2. 2026-10-03 Alias added: GHSA-w2qc-22jv-44g8

References

Advisory 2

  • TI-2021-18535 Path Traversal and Remote Code Execution in Apache HTTP Server 2.4.49 and 2.4.50 (incomplete fix of CVE-2021-41773) KEVCVSS 3.1CRITICAL 9.8
  • TI-2021-18417 Path traversal and file disclosure vulnerability in Apache HTTP Server 2.4.49 KEVCVSS 3.1CRITICAL 9.8
  • TI-2024-25716 Apache HTTP Server weakness in mod_rewrite when first segment of substitution matches filesystem path. KEVCVSS 3.1CRITICAL 9.1
  • TI-2021-17490 mod_proxy SSRF KEVCVSS 3.1CRITICAL 9.0
  • TI-2019-00184 Use after free in Apache HTTP Server KEVCVSS 3.1HIGH 7.8
  • TI-2009-03392 The TLS protocol, and the SSL protocol 3.0 and possibly earlier, as used in Microsoft… CVSS 3.1CRITICAL 9.8
See all 349 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences