SOC status:Duty analyst on shift

UK Cyber Defence
VulnerabilityModified

CVE-2021-32780

A sequence of H/2 frames delivered by an untrusted upstream server will result in Denial of Service in the presence of untrusted **upstream** servers.

HIGH 7.5EPSS 1.23%

Does this matter?

High impact if exploited, but EPSS currently rates exploitation as unlikely (1.23%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.

Description

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions Envoy transitions a H/2 connection to the CLOSED state when it receives a GOAWAY frame without any streams outstanding. The connection state is transitioned to DRAINING when it receives a SETTING frame with the SETTINGS_MAX_CONCURRENT_STREAMS parameter set to 0. Receiving these two frames in the same I/O event results in abnormal termination of the Envoy process due to invalid state transition from CLOSED to DRAINING. A sequence of H/2 frames delivered by an untrusted upstream server will result in Denial of Service in the presence of untrusted **upstream** servers. Envoy versions 1.19.1, 1.18.4 contain fixes to stop processing of pending H/2 frames after connection transition to the CLOSED state.

CVSS 3.1
7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
EPSS
1.23% probability · 69th percentile
Public exploits
None in Exploit-DB
CISA KEV
Not listed
Weakness
CWE-754
Affected
envoyproxy/envoy
Source
security-advisories@github.com
EPSS trend
0%3%5%26 October 2026: 1.23%26 October 202626 October 2026

EPSS 1.2% since 26 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.

References

Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.