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Segmentation fault when using %REQUESTED_SERVER_NAME% in log format

High
nezdolik published GHSA-j9wh-4qfm-wf2v Jun 23, 2026

Package

gomod github.com/envoyproxy/envoy (Go)

Affected versions

>=v1.37.0,<1.39

Patched versions

1.37.5 1.38.3

Description

Summary

When the %REQUESTED_SERVER_NAME(X:Y)% is used in log format and host related options is specified, like HOST_FIRST, SNI_FIRST, it's possible to crash Envoy when the specified host header is missing in the request headers.

Details

At #42659, we introduced enhanced %REQUESTED_SERVER_NAME(X:Y)% which support additional options to fallback to :authority header or x-envoy-original-host header. However, the x-envoy-original-host or :authority (especially the x-envoy-original-host) may be null but the handler of %REQUESTED_SERVER_NAME(X:Y)% doesn't check it.

PoC

Set %REQUESTED_SERVER_NAME(SNI_FIRST:ORIG)% in the log format and send a request without host rewriting, then it will crash.

Impact

Crash Envoy if specific configuration is configured.

Severity

High

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

CVE ID

CVE-2026-47220

Weaknesses

No CWEs

Credits