CVE-2021-36371Public exploitNetwork attack vector

Unauthenticated backend access via SNI-Host mismatch

Published Jul 9, 2021 · Updated Aug 4, 2024

Authentication bypass in Emissary-Ingress 1.13.9 and earlier allows remote attackers to reach mTLS-protected backends without a client certificate. TLSContext selection trusts the TLS SNI while routing selects a Mapping from the independent HTTP Host header, so the two decisions can target different hosts. The affected state requires multiple TLSContexts with at least one unprotected host; crafted unprotected SNI and protected Host values route requests to protected services without presenting a client certificate.

CVSS severity3.7
Low
EPSS probability0.74%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authentication bypass in Emissary-Ingress 1.13.9 and earlier allows remote attackers to reach mTLS-protected backends without a client certificate. TLSContext selection trusts the TLS SNI while routing selects a Mapping from the independent HTTP Host header, so the two decisions can target different hosts. The affected state requires multiple TLSContexts with at least one unprotected host; crafted unprotected SNI and protected Host values route requests to protected services without presenting a client certificate.

The record

CVE
CVE-2021-36371
Published
Jul 9, 2021
Updated
Aug 4, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-295, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 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

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Is a vulnerable build present?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

4.3NIST NVDAV:N/AC:M/Au:N/C:N/I:P/A:N
3.7NIST NVDCVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

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 exploitPublished

Weakness, pattern, technique

CWE-295Improper Certificate Validation
T1190Exploit Public-Facing Application

Public exploit references

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

Technologies

Your stack

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Your stack

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