CVE-2021-36371

Name: CVE-2021-36371
Creator: NVD / NIST
Published: 2021-07-09T21:15:08.583+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

LOWCVSS 3.7/10EPSS 0.74%

Last modified Jun 17, 2026

CVE-2021-36371 is a low-severity vulnerability rated 3.7/10 on the CVSS scale. Emissary-Ingress (formerly Ambassador API Gateway) through 1.13.9 allows attackers to bypass client certificate requirements (i.e., mTLS cert_required) on backend upstreams when more than one TLSContext is defined and at least one configuration exists that does not require client certificate authentication. The attacker must send an SNI specifying an unprotected backend and an HTTP Host header specifying a protected backend. EPSS estimates a 0.74% chance of exploitation in the next 30 days.

Description

Emissary-Ingress (formerly Ambassador API Gateway) through 1.13.9 allows attackers to bypass client certificate requirements (i.e., mTLS cert_required) on backend upstreams when more than one TLSContext is defined and at least one configuration exists that does not require client certificate authentication. The attacker must send an SNI specifying an unprotected backend and an HTTP Host header specifying a protected backend. (2.x versions are unaffected. 1.x versions are unaffected with certain configuration settings involving prune_unreachable_routes and a wildcard Host resource.)

Metrics

CVSS 3.1

3.7/10

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

EPSS Probability

0.74%

49.8th percentile

Probability of exploitation in the next 30 days. Learn more

Weakness Enumeration

CWE-295

Affected Software

Vendor	Product	Versions
Getambassador	Emissary-Ingress	<= 1.13.9

References

https://github.com/emissary-ingress/emissary/issues/3340Exploit, Third Party Advisory
https://github.com/emissary-ingress/emissary/releases/tag/v2.0.0-eaRelease Notes, Third Party Advisory
https://github.com/emissary-ingress/emissary/issues/3340Exploit, Third Party Advisory
https://github.com/emissary-ingress/emissary/releases/tag/v2.0.0-eaRelease Notes, Third Party Advisory

Timeline

Published: Jul 9, 2021
Last Modified: Jun 17, 2026
Status: Modified

Frequently Asked Questions

What is CVE-2021-36371?

How severe is CVE-2021-36371?

CVE-2021-36371 has a CVSS score of 3.7/10 (LOW severity). The EPSS model estimates a 0.74% probability of exploitation in the next 30 days.

How do I fix CVE-2021-36371?

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-2021-36371?

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

Scan your code now

Source: NVD / NIST