Security Resilience

CVE-2023-43622

DoS in Apache Http Server 2.4.55 – 2.4.58

High EPSSDoS
Published
23 October 2023
Modified
13 February 2025
Patch / advisory
CVSS Score v3.1 7.5
Click a component to see what it means
Raw vectorCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS Score 0.71 99.4th percentile
Risk Priority 83 floored blend · peak EPSS

CVSS and EPSS are reproduced from their sources (NVD, FIRST EPSS). Risk Priority is our own derived reading, not an NVD score.

Summary

CVE-2023-43622 is a high-severity Uncontrolled Resource Consumption (CWE-400) vulnerability in Apache Http Server. Its CVSS base score is 7.5 (High).

Operationally, ranked in the top 0.6% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.

Deeper analysis AI-assisted summary

Synthesised by an AI model from the NVD description and linked references — a reading aid, not an authoritative source.

CVE-2023-43622 is a denial-of-service vulnerability in Apache HTTP Server versions 2.4.55 through 2.4.57. An attacker who opens an HTTP/2 connection with an initial window size of zero can cause the server to block handling of that connection indefinitely, exhausting available worker processes in a manner similar to the classic Slowloris attack pattern. The flaw is tracked under CWE-400 and carries a CVSS 3.1 score of 7.5.

Unauthenticated remote attackers can exploit the issue over the network by establishing a small number of such connections, rendering the server unavailable to legitimate clients without requiring authentication or user interaction. The attack succeeds because the server does not enforce its configured connection timeout on these specially crafted HTTP/2 streams.

Official advisories from the Apache HTTP Server project state that the vulnerability is resolved in version 2.4.58, which terminates affected connections once the timeout expires. NetApp has also published corresponding security bulletins referencing the same fix.

The EPSS score for this CVE currently stands at 0.5954 with a recorded peak of 0.6322, indicating sustained and moderately elevated exploitation interest since disclosure.

EU & UK References

Vulnerability Data

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…

more

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.

CWE(s)

Related Threats

CVEs Like This One

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CVE-2026-73636Same product: Apache Http Server

Affected Assets

apache
http server
2.4.55 — 2.4.58

Mitigating Controls

Likely Mitigating Controls AI

Per-CVE control mapping for this CVE has not run yet; the list below is derived from the weakness types (CWEs) cited in the NVD entry.

addresses: CWE-400

Limiting concurrent sessions directly prevents uncontrolled resource consumption by capping the number of active sessions per user or account.

addresses: CWE-400

Analysis identifies uncontrolled resource consumption indicative of denial-of-service or abuse attempts.

addresses: CWE-400

Contingency plan testing includes resource exhaustion scenarios to verify recovery, making it harder for attackers to sustain exploits that cause uncontrolled consumption.

addresses: CWE-400

Updated contingency plans include current procedures to detect, contain, and recover from resource exhaustion, limiting an attacker's ability to sustain impact from uncontrolled consumption.

addresses: CWE-400

Alternate site allows resumption of operations if resource exhaustion at the primary site is exploited to cause unavailability.

addresses: CWE-400

Alternate telecommunications services enable resumption of essential functions when primary services become unavailable due to uncontrolled resource consumption.

addresses: CWE-400

The team can analyze and respond to resource exhaustion incidents, reducing the impact of attacks that exploit uncontrolled consumption weaknesses.

addresses: CWE-400

Timely maintenance support and spare parts enable rapid recovery from failures induced by uncontrolled resource consumption, shortening the impact window of denial-of-service attacks.

Mitigating Controls (ISO/IEC 27001:2022 Annex A) AI

Derived directly from the weakness types (CWEs) cited in the NVD entry via our AI-authored CWE→ISO cross-walk (authority under review) — links open the control.

finds

Pre-agreed severity-based prioritization and resource allocation during incident triage reduce the likelihood that an attacker-induced resource exhaustion will overwhelm the organization before corrective action is taken.

finds

Early notification of anomalous resource consumption or system malfunctions enables throttling or isolation before availability is lost.

A.8.15 Logging partial match
finds

Specifying log storage limits and rotation procedures reduces the risk that unbounded log growth will exhaust disk or memory resources and cause denial of service.

finds

Resource-utilization monitoring and alerting on bottlenecks or overloads limits the impact of denial-of-service or resource-exhaustion attacks.

blocks

A.8.20 implements network-level protections (firewalls, segmentation, protocol hardening, monitoring, authentication of systems/devices) that can limit abuse of a resource-consuming weakness but do not stop the weakness from being exploitable; the flaw remains present in the product and can still be triggered from an authorized or internal context.

blocks

Monitoring network service usage and applying controls to restrict access when necessary limits an attacker’s ability to consume excessive resources through unrestricted or unauthenticated service calls.

Hardening callouts derived

DISA STIG baselines are authored against specific weaknesses. Where this CVE cites a broad weakness class, the mapping is not asserted at that abstraction (owner ruling, 2026-09-25: grade only at Base and below), so no rule is shown here rather than a rule shown against the wrong grain.

  • No fine-grained STIG row for CWE-400, a class-level weakness. Rules are authored against its narrower children: CWE-770.

References