CVE-2023-35944

Envoy vulnerable to incorrect handling of HTTP requests and responses with mixed case schemes

MEDIUM
5.3
CVSS Score
Published: July 25, 2023 at 06:35 PM UTC
Updated: June 17, 2026 at 06:05 AM UTC
1 product affected across 1 vendorEnvoy

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Severity
MEDIUM5.3
Exploit prediction
EPSS 0.7%
SSVC
PoC

Description

Envoy is an open source edge and service proxy designed for cloud-native applications. Envoy allows mixed-case schemes in HTTP/2, however, some internal scheme checks are case-sensitive. Prior to versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, this can lead to the rejection of requests with mixed-case schemes such as `htTp` or `htTps`, or the bypassing of some requests such as `https` in unencrypted connections. With a fix in versions 1.27.0, 1.26.4, 1.25.9, 1.24.10, and 1.23.12, Envoy will now lowercase scheme values by default, and change the internal scheme checks that were case-sensitive to be case-insensitive. There are no known workarounds for this issue.

Affected

Our own answer: ranges merged, affected separated from platform-only, with confidence and review flags.

v < 1.23.12v < 1.24.10v < 1.25.9v < 1.26.41.23.0 ≤ v < 1.23.121.24.0 ≤ v < 1.24.101.25.0 ≤ v < 1.25.91.26.0 ≤ v < 1.26.4
Affected range stops below 1.23.12, so it looks safe — our inference, not a vendor statement
Affected range stops below 1.24.10, so it looks safe — our inference, not a vendor statement
Affected range stops below 1.25.9, so it looks safe — our inference, not a vendor statement
Affected range stops below 1.26.4, so it looks safe — our inference, not a vendor statement

Remediation

No guide yet

No remediation guidance has been written for this CVE yet, and no fixed version or vendor advisory is recorded against it.

References (1)

SSVC — Action Prioritization

SSVCPoCNot automatableTotal impact

SSVC signals action urgency (what to patch first), separate from CVSS which measures severity.

CVSS

Attack Vector
NETWORK
Complexity
LOW
Privileges
NONE
User Interaction
NONE
Scope
UNCHANGED
Confidentiality
NONE
Integrity
LOW
Availability
NONE
Vector?

Quick Info

StatusMODIFIED
CWE
CWE-20CWE-444

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