CVE-2021-32777

Name: CVE-2021-32777
Creator: NVD / NIST
Published: 2021-08-24T21:15:06.97+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

HIGHCVSS 8.3/10EPSS 3.33%

Last modified Jun 17, 2026

CVE-2021-32777 is a high-severity vulnerability rated 8.3/10 on the CVSS scale. Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions when ext-authz extension is sending request headers to the external authorization service it must merge multiple value headers according to the HTTP spec. EPSS estimates a 3.33% chance of exploitation in the next 30 days.

Description

Envoy is an open source L7 proxy and communication bus designed for large modern service oriented architectures. In affected versions when ext-authz extension is sending request headers to the external authorization service it must merge multiple value headers according to the HTTP spec. However, only the last header value is sent. This may allow specifically crafted requests to bypass authorization. Attackers may be able to escalate privileges when using ext-authz extension or back end service that uses multiple value headers for authorization. A specifically constructed request may be delivered by an untrusted downstream peer in the presence of ext-authz extension. Envoy versions 1.19.1, 1.18.4, 1.17.4, 1.16.5 contain fixes to the ext-authz extension to correctly merge multiple request header values, when sending request for authorization.

Metrics

CVSS 3.1

8.3/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

EPSS Probability

3.33%

87.1th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

Affected Software

Vendor	Product	Versions
Envoyproxy	Envoy	>= 1.16.0, < 1.16.5
Envoyproxy	Envoy	>= 1.17.0, < 1.17.4
Envoyproxy	Envoy	>= 1.18.0, < 1.18.4
Envoyproxy	Envoy	1.19.0

References

https://github.com/envoyproxy/envoy/security/advisories/GHSA-6g4j-5vrw-2m8hThird Party Advisory
https://www.envoyproxy.io/docs/envoy/v1.19.0/version_history/version_historyRelease Notes, Vendor Advisory
https://github.com/envoyproxy/envoy/security/advisories/GHSA-6g4j-5vrw-2m8hThird Party Advisory
https://www.envoyproxy.io/docs/envoy/v1.19.0/version_history/version_historyRelease Notes, Vendor Advisory

Timeline

Published: Aug 24, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-32777?

How severe is CVE-2021-32777?

CVE-2021-32777 has a CVSS score of 8.3/10 (HIGH severity). The EPSS model estimates a 3.33% probability of exploitation in the next 30 days.

How do I fix CVE-2021-32777?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2021-32777?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST