CVE-2026-73551: Envoy: Path normalization does not handle dot and dotdot segments with parameters

Severity: medium (CVSS 5.3 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-09-21 · updated 2026-10-05
Weakness: CWE-647

Description

Envoy is an open source edge and service proxy designed for cloud-native applications. Prior to 1.36.10, 1.37.6, 1.38.4, and 1.39.1, Envoy's URL normalization does not recognize dot and dotdot path segments when they carry semicolon parameters. A request such as /user/..;foo=bar/admin is therefore not canonicalized to /admin even when path normalization is enabled. If an upstream interprets the segment according to RFC 3986 while Envoy applies routing or RBAC to the uncollapsed path, a remote client can cause path confusion and bypass path-based security policy. The relevant scope boundary is that the security consequence depends on a downstream/upstream path interpretation mismatch or a path-based Envoy decision. This issue is fixed in versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1.

Affected products

envoyproxy envoy: before 1.36.10; from 1.37.0 before 1.37.6; from 1.38.0 before 1.38.4; from 1.39.0 before 1.39.1 — fixed in 1.36.10, 1.37.6, 1.38.4, 1.39.1

How to fix

Upgrade to a fixed version: envoyproxy envoy 1.36.10, 1.37.6, 1.38.4, 1.39.1. Check the vendor advisory for mitigations.

References

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