CVE-2021-31920Public exploitNetwork attack vector

Authorization bypass via inconsistent path normalization

Published May 27, 2021 · Updated Aug 3, 2024

Incorrect authorization in Istio before 1.8.6 and 1.9.0 through 1.9.4 allows remote authenticated users to access protected resources. Istio compares an unnormalized request path against an authorization rule while some backends merge repeated slashes or decode escaped slash characters before routing. The bypass requires a vulnerable DENY paths or ALLOW notPaths policy and grants access to backend resources that the policy was intended to block.

CVSS severity8.1
High
EPSS probability1.17%
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 1.8.6 and 1.9.0 through 1.9.4 allows remote authenticated users to access protected resources. Istio compares an unnormalized request path against an authorization rule while some backends merge repeated slashes or decode escaped slash characters before routing. The bypass requires a vulnerable DENY paths or ALLOW notPaths policy and grants access to backend resources that the policy was intended to block.

The record

CVE
CVE-2021-31920
Published
May 27, 2021
Updated
Aug 3, 2024
Vendor
Unknown vendor
Product
Unknown product
Classifications
CWE-706, T1190
Attack vector
network
Privileges
authenticated

Timeline

How it unfolded

  1. May 27, 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?

Affected buildAffected product and version details are unavailable.

What conditions does exploitation require?

Attack vectornetwork
Required privilegesauthenticated

What is affected?

Affected products and versions are unavailable in this record.

Published CVSS scores

6.5NIST NVDCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:N/A:N
8.1IstioCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
4.0NIST NVDAV:N/AC:L/Au:S/C:P/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
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitPublished

Weakness, pattern, technique

CWE-706Use of Incorrectly-Resolved Name or Reference
T1190Exploit Public-Facing Application

Public exploit references

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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