Exploited. On CISA's list since 2023-10-10.
HTTP/2 Rapid Reset Attack Vulnerability
CVE-2023-44487 · IETF HTTP/2 · Published 2023-10-10
How bad would it be?
7.5 out of 10
CVSS rates it high.
How likely is it to be used?
over 99%
Estimated chance of exploitation in the next 30 days, among the top 1% of all scored flaws (EPSS, 2026-10-29).
Is it already being used?
Yes
CISA has seen it exploited in real attacks. For US government agencies the fix is deadline passed 1095 days ago (2023-10-31).
What CISA says to do
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
HTTP/2 contains a rapid reset vulnerability that allows for a distributed denial-of-service attack (DDoS).
What the flaw is
The HTTP/2 protocol allows a denial of service (server resource consumption) because request cancellation can reset many streams quickly, as exploited in the wild in August through October 2023.
From the NVD.
Fixes and advisories
Learn this
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Understand the kind of weakness behind this flaw. These resources teach the weakness, rather than reproduce this specific CVE. Follow the vendor's advice above to fix the affected product.
CWE-400 · CISA KEV; NVD record: 134c704f-9b21-4f2e-91b3-4a467353bcc0. We have not selected a close learning match for this label.
CWE is a catalogue of weakness types. Labels come from the sources shown and can differ or change. Resource matches reviewed 16 October 2026.
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Exploited flaws from CISA's KEV catalogue. Chance of exploitation from EPSS by FIRST. Descriptions and scores from the NVD. This product uses the NVD API but is not endorsed or certified by the NVD.