CVE-2021-29492Network attack vector

Unauthorized backend access via undecoded escaped slashes

Published May 28, 2021 · Updated Aug 3, 2024

Authorization bypass in Envoy 1.18.2 and earlier allows remote attackers to reach path-restricted backend resources via escaped slashes. Envoy evaluates RBAC or JWT path rules without decoding %2F and %5C, while a backend that later decodes and normalizes the path can route the request to a protected resource. Exploitation requires path-based RBAC or JWT enforcement and a backend that treats escaped and literal slash characters equivalently.

CVSS severity8.3
High
EPSS probability66.21%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Authorization bypass in Envoy 1.18.2 and earlier allows remote attackers to reach path-restricted backend resources via escaped slashes. Envoy evaluates RBAC or JWT path rules without decoding %2F and %5C, while a backend that later decodes and normalizes the path can route the request to a protected resource. Exploitation requires path-based RBAC or JWT enforcement and a backend that treats escaped and literal slash characters equivalently.

The record

CVE
CVE-2021-29492
Published
May 28, 2021
Updated
Aug 3, 2024
Vendor
Envoy Proxy
Product
Envoy
Classifications
CWE-551, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. May 28, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 3, 2024Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=<= 1.18.2

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Envoy Proxy · Envoyversion=<= 1.18.2

Published CVSS scores

8.3BitnamiCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:L

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

Daily unique IPsNo honeypot observations are available for this CVE in the selected window.

No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectornetwork
Privilegesunauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-551Incorrect Behavior Order: Authorization Before Parsing and Canonicalization
T1190Exploit Public-Facing Application

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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