VulnerabilityPublished 21 Sep 2026Updated 28 Sep 2026

CVE-2026-73551: envoyproxy envoy · Use of Non-Canonical URL Paths for Authorization Decisions

Affects envoyproxy envoySource CVE Database V5

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Not known to be exploited · CVSS 5.3 Medium · fixed in 1.39.1 : update envoyproxy envoy when convenient.

Data as of 5 Nov 2026, 00:01 UTC

CVSS 3.1 base score

5.3Medium

How severe the flaw is on the 0–10 CVSS scale.

EPSS: 0.5% chance of exploitation in 30 days – higher than 44% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 1.39.1, 1.38.4, 1.37.6 +1

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:N

Attack Vector: Network
Attack Complexity: Low
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: Low
Integrity: None
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: Low: Specialized access conditions or extenuating circumstances do not exist. An attacker can expect repeatable success against the vulnerable component.
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: Low: There is some loss of confidentiality. Access to some restricted information is obtained, but the attacker does not have control over what information is obtained, or the amount or kind of loss is limited. The information disclosure does not cause a direct, serious loss to the impacted component.
Integrity: None: There is no loss of integrity within the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 21 Sep 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 5 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade envoy and envoyproxy/envoy to 1.39.1, 1.38.4, 1.37.6 or 1.36.10.

Affected software

Product	Affected	Fixed in
envoyproxyenvoy	Affected >=1.39.0 <1.39.1	Fixed in 1.39.1
envoyproxyenvoy	Affected >=1.38.0 <1.38.4	Fixed in 1.38.4
envoyproxyenvoy	Affected >=1.37.0 <1.37.6	Fixed in 1.37.6
envoyproxyenvoy	Affected <1.36.10	Fixed in 1.36.10
GitHubenvoyproxy/envoy`pkg:github/envoyproxy/envoy`Other threats	Affected <1.36.10 >=1.37.0 <1.37.6 >=1.38.0 <1.38.4 >=1.39.0 <1.39.1	Fixed in 1.36.10 1.37.6 1.38.4 1.39.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

Upgrade Envoy to versions 1.36.10, 1.37.6, 1.38.4, or 1.39.1 or later where the URL normalization issue is fixed. No other mitigation is indicated by the vendor advisory. Patch status is confirmed by the fixed versions listed.

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.

Impact

The vulnerability allows remote attackers to cause path confusion due to inconsistent URL normalization between Envoy and upstream services. This can lead to bypassing path-based authorization or routing policies enforced by Envoy, potentially exposing restricted resources. The impact is limited to confidentiality loss (partial bypass) without integrity or availability effects.

Summary

Envoy proxy's URL normalization prior to versions 1.36.10, 1.37.6, 1.38.4, and 1.39.1 fails to recognize dot (.) and dotdot (..) path segments when they include semicolon parameters, such as in the path '/user/..;foo=bar/admin'. This causes Envoy to not canonicalize the path to '/admin' even when path normalization is enabled. If an upstream service interprets the path according to RFC 3986 and collapses these segments, a mismatch occurs between Envoy's routing or RBAC decisions and the upstream interpretation. This discrepancy can be exploited by remote clients to bypass path-based security controls. The issue is fixed in the specified patched versions.

CWE-647Use of Non-Canonical URL Paths for Authorization Decisions (opens in a new tab)
Variant weaknessLikelihood of exploit: High
The product defines policy namespaces and makes authorization decisions based on the assumption that a URL is canonical.
Architecture and Design
Make access control policy based on path information in canonical form, with all alternate encodings rejected (which can be accomplished by a default deny rule). Consider very restrictive regular expressions to validate that the path is in the expected form.
OWASP ASVS 4.0.3
V8.3.8 (opens in a new tab)
V13.4.2 (opens in a new tab)
V7.2.2 (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

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Exploitation evidence

What to do

Affected software

Description

AI analysisMachine-generated, updated 29 Sep 2026, 02:04 UTC

WeaknessesCWE-647

Technical details

References

Community reviews

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