CVE-2021-39162Network attack vector

Proxy crash via invalid HTTP/2 state transition

Published Sep 9, 2021 · Updated Aug 4, 2024

Denial of service in Pomerium 0.15.0 allows remote attackers controlling an upstream server to crash the proxy via HTTP/2 frames. Envoy closes an idle HTTP/2 connection on GOAWAY, then incorrectly changes the closed connection to draining when a co-delivered SETTINGS frame sets the maximum concurrent streams to zero. Exploitation requires an untrusted upstream server and terminates the Pomerium process, interrupting proxied access until service recovery.

CVSS severity8.6
High
EPSS probability1.64%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Denial of service in Pomerium 0.15.0 allows remote attackers controlling an upstream server to crash the proxy via HTTP/2 frames. Envoy closes an idle HTTP/2 connection on GOAWAY, then incorrectly changes the closed connection to draining when a co-delivered SETTINGS frame sets the maximum concurrent streams to zero. Exploitation requires an untrusted upstream server and terminates the Pomerium process, interrupting proxied access until service recovery.

The record

CVE
CVE-2021-39162
Published
Sep 9, 2021
Updated
Aug 4, 2024
Vendor
Pomerium
Product
Pomerium
Classifications
CWE-754, T1499.004
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Sep 9, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=>= 0.15.0, < 0.15.1

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Pomerium · Pomeriumversion=>= 0.15.0, < 0.15.1

Published CVSS scores

5.0NISTAV:N/AC:L/Au:N/C:N/I:N/A:P
8.6NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:N/I:N/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-754Improper Check for Unusual or Exceptional Conditions
T1499.004Endpoint Denial of Service: Application or System Exploitation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo