CVE-2023-35944Public exploitNetwork attack vector

HTTP filter bypass via mixed-case schemes

Published Jul 25, 2023 · Updated Oct 23, 2024

Improper input validation in Envoy allows remote attackers to bypass HTTP filters with mixed-case HTTP/2 schemes. HTTP and related filters accept mixed-case scheme values but compare them case-sensitively with lowercase http or https, producing inconsistent security decisions. An unauthenticated network request is sufficient; for example, the OAuth2 filter treats htTp as https and can skip checks limited to cleartext HTTP.

CVSS severity8.2
High
EPSS probability0.70%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

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Summary

What happened

Improper input validation in Envoy allows remote attackers to bypass HTTP filters with mixed-case HTTP/2 schemes. HTTP and related filters accept mixed-case scheme values but compare them case-sensitively with lowercase http or https, producing inconsistent security decisions. An unauthenticated network request is sufficient; for example, the OAuth2 filter treats htTp as https and can skip checks limited to cleartext HTTP.

The record

CVE
CVE-2023-35944
Published
Jul 25, 2023
Updated
Oct 23, 2024
Vendor
Envoy Proxy
Product
Envoy
Classifications
CWE-444, CWE-20, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 25, 2023CVE publishedPublication date reported by the CVE source.
  2. Oct 23, 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=< 1.23.12
  2. Affected versionversion=>= 1.24.0, < 1.24.10
  3. Affected versionversion=>= 1.25.0, < 1.25.9
  4. Affected versionversion=>= 1.26.0, < 1.26.4

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Envoy Proxy · Envoyversion=< 1.23.12; version=>= 1.24.0, < 1.24.10; version=>= 1.25.0, < 1.25.9; version=>= 1.26.0, < 1.26.4

Published CVSS scores

8.2GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N
5.3NIST National Vulnerability DatabaseCVSS:3.1/AV:N/AC:L/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-444Inconsistent Interpretation of HTTP Requests
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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