Is CVE-2021-32778 actively exploited?

No active exploitation of CVE-2021-32778 has been confirmed so far. Continue monitoring, as exploit status can change.

Can CVE-2021-32778 be exploited remotely?

Yes. CVE-2021-32778 is exploitable remotely over the network (CVSS attack vector: Network).

What is the CVSS score of CVE-2021-32778?

CVE-2021-32778 has a CVSS score of 7.5 (HIGH).

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HIGH

CVE-2021-32778

CWE-834Published: August 24, 2021· Updated: Jun 17, 2026

7.5

CVSS v3.1

Official Description

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions envoy’s procedure for resetting a HTTP/2 stream has O(N^2) complexity, leading to high CPU utilization when a large number of streams are reset. Deployments are susceptible to Denial of Service when Envoy is configured with high limit on H/2 concurrent streams. An attacker wishing to exploit this vulnerability would require a client opening and closing a large number of H/2 streams. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to reduce time complexity of resetting HTTP/2 streams. As a workaround users may limit the number of simultaneous HTTP/2 dreams for upstream and downstream peers to a low number, i.e. 100.

NVD Source

Technical Analysis

CVE-2021-32778 can be exploited remotely over the network without requiring physical or adjacent access, significantly expanding the attack surface for threat actors.

The vulnerability requires no privileges and no user interaction, making it a prime target for automated exploitation campaigns and worm-like propagation.

A successful exploit results in availability disruption (denial of service), with a CVSS base score of 7.5.