CVE-2023-27493Public exploitNetwork attack vector

Security policy bypass via unsanitized generated headers

Published Apr 4, 2023 · Updated Feb 11, 2025

HTTP request smuggling in affected Envoy versions allows remote attackers to bypass proxy security policy via crafted request properties. When configured to synthesize upstream headers from downstream request or certificate properties, the HTTP header-generation path copies CR or LF bytes into header values without validation or escaping. Exploitation requires that header-addition configuration and a crafted HTTP request or mTLS client certificate; successful injection causes an upstream service to parse attacker-controlled bytes as a second request.

CVSS severity8.1
High
EPSS probability0.51%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

HTTP request smuggling in affected Envoy versions allows remote attackers to bypass proxy security policy via crafted request properties. When configured to synthesize upstream headers from downstream request or certificate properties, the HTTP header-generation path copies CR or LF bytes into header values without validation or escaping. Exploitation requires that header-addition configuration and a crafted HTTP request or mTLS client certificate; successful injection causes an upstream service to parse attacker-controlled bytes as a second request.

The record

CVE
CVE-2023-27493
Published
Apr 4, 2023
Updated
Feb 11, 2025
Vendor
Envoy Proxy
Product
Envoy
Classifications
CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Apr 4, 2023CVE publishedPublication date reported by the CVE source.
  2. Feb 11, 2025Record 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=< 1.22.9
  2. Affected versionversion=>= 1.23.0, < 1.23.6
  3. Affected versionversion=>= 1.24.0, < 1.24.4
  4. Affected versionversion=>= 1.25.0, < 1.25.3

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Envoy Proxy · Envoyversion=< 1.22.9; version=>= 1.23.0, < 1.23.6; version=>= 1.24.0, < 1.24.4; version=>= 1.25.0, < 1.25.3

Published CVSS scores

8.1GitHubCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/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-20Improper Input 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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