CVE-2021-39156Network attack vector

Authorization bypass via unstripped URI fragments

Published Aug 24, 2021 · Updated Aug 4, 2024

Incorrect authorization in Istio before 1.9.8, 1.10.0 through 1.10.3, and 1.11.0 allows remote attackers to bypass URI path policies. Istio evaluates a fragment-bearing path against operation.paths or operation.notPaths before Envoy routes its normalized, percent-encoded form to the backend. Exposure requires DENY rules using operation.paths or ALLOW rules using operation.notPaths, and bypass grants access those policies intended to block.

CVSS severity8.1
High
EPSS probability1.18%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Incorrect authorization in Istio before 1.9.8, 1.10.0 through 1.10.3, and 1.11.0 allows remote attackers to bypass URI path policies. Istio evaluates a fragment-bearing path against operation.paths or operation.notPaths before Envoy routes its normalized, percent-encoded form to the backend. Exposure requires DENY rules using operation.paths or ALLOW rules using operation.notPaths, and bypass grants access those policies intended to block.

The record

CVE
CVE-2021-39156
Published
Aug 24, 2021
Updated
Aug 4, 2024
Vendor
Istio
Product
Istio
Classifications
CWE-863, CWE-706, T1190
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Aug 24, 2021CVE publishedPublication date reported by the CVE source.
  2. Aug 4, 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=>= 1.10.0, < 1.10.4
  2. Affected versionversion=>= 1.11.0, < 1.11.1
  3. Affected versionversion=< 1.9.8

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

Istio · Istioversion=>= 1.10.0, < 1.10.4; version=>= 1.11.0, < 1.11.1; version=< 1.9.8

Published CVSS scores

8.1GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:N
5.0NISTAV:N/AC:L/Au:N/C:P/I:N/A:N
7.5NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N

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-863Incorrect Authorization
CWE-706Use of Incorrectly-Resolved Name or Reference
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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