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TI-2023-18005 Aliases CVE-2023-35944

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

Priority HIGH 71CWE-20Published · Updated

Key facts

Attack vector
Network
Privileges required
None
User interaction
None
Attack complexity
Low
Impact type
—
Confidentiality · integrity · availability
High · Low · None
Fix status
Fixed

Attack profile from CVSS 3.1 · CNA. Fix status from CNA and Red Hat.

Summary

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.

Why it matters now

Exploitation Proof of concept CISA SSVC · not in CISA KEV
EPSS 0.00704 53rd percentileScored 2026-11-07
Public exploit Yes 1 exploit referenceTagged by NVD
Fix Fixed envoy (envoyproxy): 1.26.4, 1.25.9, 1.24.10 +1Red Hat: 3 advisories

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation
Poc
Automatable
No
Technical impact
Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

VendorProductAffected versionsFixed inStatusSource
envoyproxyenvoy1.26.0 to before 1.26.4; 1.25.0 to before 1.25.9; 1.24.0 to before 1.24.10; before 1.23.121.26.4, 1.25.9, 1.24.10, 1.23.12Patch availableCNA
  • envoy Vendorenvoyproxy Affected 1.26.0 to before 1.26.4; 1.25.0 to before 1.25.9; 1.24.0 to before 1.24.10; before 1.23.12 Fixed in 1.26.4, 1.25.9, 1.24.10, 1.23.12 Patch available CNA

CPE configurations NVD · 1

CPEVersionsRoleVendor
cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:*1.23.0 to before 1.23.12; 1.24.0 to before 1.24.10; 1.25.0 to before 1.25.9; 1.26.0 to before 1.26.4Vulnerableenvoyproxy
  • cpe:2.3:a:envoyproxy:envoy:*:*:*:*:*:*:*:* Versions 1.23.0 to before 1.23.12; 1.24.0 to before 1.24.10; 1.25.0 to before 1.25.9; 1.26.0 to before 1.26.4 Vulnerable ·envoyproxy

Remediation

  • Fix · CNA envoy (envoyproxy) Fixed in 1.26.4, 1.25.9, 1.24.10, 1.23.12

Red Hat 3 advisories

  • RHSA-2023:5175 Released 2023-09-14 · Red Hat rating Important
    Red Hat OpenShift Service Mesh 2.2.10 security update
    • RHOSSM 2.2 for RHEL 8 openshift-service-mesh/proxyv2-rhel8
  • RHSA-2023:4625 Released 2023-08-11 · Red Hat rating Important
    Red Hat OpenShift Service Mesh Containers for 2.4.2 security update
    • RHOSSM 2.4 for RHEL 8 openshift-service-mesh/proxyv2-rhel8
  • RHSA-2023:4624 Released 2023-08-11 · Red Hat rating Important
    Red Hat OpenShift Service Mesh Containers for 2.3.6 security update
    • RHOSSM 2.3 for RHEL 8 openshift-service-mesh/proxyv2-rhel8

Vendor assessments

Red Hat

Red Hat rating: Important. Red Hat's page for this CVE →

ProductStatusPlan or fix
RHOSSM 2.2 for RHEL 8Fixed RHSA-2023:5175
RHOSSM 2.3 for RHEL 8Fixed RHSA-2023:4624
RHOSSM 2.4 for RHEL 8Fixed RHSA-2023:4625
Not affected: 3 products
  • RHOSSM 2.2 for RHEL 8
  • RHOSSM 2.3 for RHEL 8
  • RHOSSM 2.4 for RHEL 8

Timeline

  1. 2026-10-02 Threatist record created from CVE-2023-35944

References

Exploit 1

  • TI-2026-79288 Out-of-bounds write in Google Brotli decoder KEVCVSS 4.0CRITICAL 9.2
  • TI-2023-23979 The HTTP/2 protocol allows a denial of service (server resource consumption) because… KEVCVSS 3.1HIGH 7.5
  • TI-2024-20001 HTTP/2: CPU exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2024-18524 HTTP/2: memory exhaustion due to CONTINUATION frame flood CVSS 3.1HIGH 7.5
  • TI-2023-12215 Envoy client may fake the header `x-envoy-original-path` CVSS 3.1CRITICAL 9.1
  • TI-2023-18002 Envoy vulnerable to OAuth2 credentials exploit with permanent validity CVSS 3.1CRITICAL 9.8
See all 126 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences