CVE-2023-43622
Published: 23 October 2023
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 1.7% of CVEs by exploit likelihood; it is not currently listed in the CISA KEV catalog.
Deeper analysis
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
- 🇪🇺 ENISA EUVD: EUVD-2023-48022
Vulnerability details
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…
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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
No named actor attribution yet. ATT&CK technique mapping in progress for this CVE.
Affected Assets
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.
Limiting concurrent sessions directly prevents uncontrolled resource consumption by capping the number of active sessions per user or account.
Analysis identifies uncontrolled resource consumption indicative of denial-of-service or abuse attempts.
Contingency plan testing includes resource exhaustion scenarios to verify recovery, making it harder for attackers to sustain exploits that cause uncontrolled consumption.
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.
Alternate site allows resumption of operations if resource exhaustion at the primary site is exploited to cause unavailability.
Alternate telecommunications services enable resumption of essential functions when primary services become unavailable due to uncontrolled resource consumption.
The team can analyze and respond to resource exhaustion incidents, reducing the impact of attacks that exploit uncontrolled consumption weaknesses.
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.