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

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.

Published: 2023-10-23 Last update: 2025-02-13 Assigner: [email protected] Source: [email protected]
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2023-43622 is rated Moderate Risk (60.7/100): CVSS High severity, with high exploitation likelihood (EPSS 59.54%, 98th percentile). EPSS ranks this CVE among the most likely to be exploited in the near term. High exploitation likelihood—assess exposure and prioritize remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2023-43622

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-03 63.22% 59.54% -3.68%
2 2026-05-16 61.26% 63.22% +1.96%
3 2026-04-03 — 61.26% —

Full EPSS history (47 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2023-43622

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2023-43622

OS Trackers for CVE-2023-43622

vendor priority summary link
alpine — CVE-2023-43622: 1 source package rows (apache2); 7 state rows across 7 repos (3.17-main, 3.18-main, 3.19-main, 3.20-main, 3.21-main, 3.22-main, edge-main); fixed 7, open 0. https://security.alpinelinux.org/vuln/CVE-2023-43622
debian not yet assigned CVE-2023-43622 not yet assigned priority: Debian including 1 source packages (apache2), 5 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 5. https://security-tracker.debian.org/tracker/CVE-2023-43622
redhat medium — https://access.redhat.com/security/cve/CVE-2023-43622
suse high CVE-2023-43622 severity important: SUSE including 24 source package names (apache2, apache2-2.4.58-1.1, …), 185 product×package rows across 42 product lines (SUSE CaaS Platform 4.0, SUSE Enterprise Storage 7.1, … (42 product lines)): Known Not Affected 169, Fixed 16. https://www.suse.com/security/cve/CVE-2023-43622/
ubuntu low CVE-2023-43622 low priority: Ubuntu including 1 source packages (apache2), 8 status rows across 8 suites (bionic, focal, jammy, lunar, mantic, trusty, upstream, xenial): not-affected 5, released 3. https://ubuntu.com/security/CVE-2023-43622

Affected software / configurations for CVE-2023-43622

Vendor Product Version Raw CPE
apache http_server >= 2.4.55, < 2.4.58 cpe:2.3:a:apache:http_server:*:*:*:*:*:*:*:*

References for CVE-2023-43622

cvelogic Threat Intelligence