CVE-2023-43622
A public proof of concept exists; no exploitation attested.
- Published2023-10-23
- Fixed in2.4.58
- WeaknessCWE-400
Am I affected?
Debian, Ubuntu or Red Hat sometimes backport a fix without changing the upstream version number: such a version reads « to verify », never « affected ».With a domain, we read the version its public headers and pages expose. A distribution build can carry the fix under an older number.
Description
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.
Timeline
dates in UTC- 2023-10-2307:15CVE publishedNVD
- 2026-10-2319:23First public proof of conceptPoC-in-GitHub
- 2026-10-2319:23EPSS crossed 10 %FIRST EPSS
Observed activity
isMalicious corpus · updated 2026-10-23 21:37 UTCBlock these indicators
- Firewall list (EDL, text): https://api.ismalicious.com/edl/cve/CVE-2023-43622?format=txt
- CSV export: https://api.ismalicious.com/edl/cve/CVE-2023-43622?format=csv
- TAXII collection of exploited CVEs
- The EDL and CSV take an API key on the Pro plan.
Versions per branch
NVD · OSV| Branch | Affected | Fixed in | Source |
|---|---|---|---|
| 2.4 | ≥ 2.4.55, < 2.4.58 | 2.4.58 | NVD · OSV |
as publishedRanges as NVD and OSV publish them; a distribution’s build can be fixed under an older number.
Distribution builds and vendor advisories
Packages from OSV.dev and products from the vendors' CSAF advisories.
version not verifiedVersions not verified: read as OSV.dev and the vendors publish them, not checked against each vendor's release list.
Packages
- mod_http2AlmaLinux:9all versions · fixed in 2.0.26-1.el9
Fix
- Update Apache HTTP Server to 2.4.58
Advisories and patches
- httpd.apache.orgVendor Advisory
Detection
read 2026-10-23 19:23 UTC- Nuclei template
- none so far ProjectDiscovery
- Exploit-DB
- no entry Exploit-DB
Sources
- CISA-ADPSSVC decisionpoc2024-09-11
- OpenCVESSVC decisionpoc—
- NVDCVSS 3.17.5read 2026-10-23
- CNAweakness (CWE)CWE-400read 2026-10-23
- FIRST EPSSEPSS score68.8 %read 2026-10-23
- PoC-in-GitHubproof of concept1read 2026-10-23
- OSVaffected packages—
Technical details
- CVSS v3 Vector
- CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- Published
- 2023-10-23
- Last Modified
- 2026-06-17
- NVD status
- Modified
Frequently asked questions
What is CVE-2023-43622?
Is CVE-2023-43622 actively exploited?
What is the CVSS score for CVE-2023-43622?
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Related vulnerabilities
Same product first, then the same vendor advisory and the same publication week.