CVE-2021-21291Network attack vector

Open redirect via dot-stripped domain suffix matching

Published Feb 2, 2021 · Updated Aug 3, 2024

Open redirect in OAuth2 Proxy before 7.0.0 allows remote attackers to send users to attacker-controlled domains through crafted redirect URLs. The redirect validator strips the leading dot from a whitelisted domain and then uses a suffix match, so badexample.com satisfies a rule intended for .example.com. The whitelist-domain feature must be enabled and a user must follow the crafted redirect; the flaw changes the navigation target without directly exposing upstream data.

CVSS severity4.7
Medium
EPSS probability1.58%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
Coverage for this vulnerability

See if you're affected

Explore vulnerability checks for your environment with Hinoki.

Book a demo

Summary

What happened

Open redirect in OAuth2 Proxy before 7.0.0 allows remote attackers to send users to attacker-controlled domains through crafted redirect URLs. The redirect validator strips the leading dot from a whitelisted domain and then uses a suffix match, so badexample.com satisfies a rule intended for .example.com. The whitelist-domain feature must be enabled and a user must follow the crafted redirect; the flaw changes the navigation target without directly exposing upstream data.

The record

CVE
CVE-2021-21291
Published
Feb 2, 2021
Updated
Aug 3, 2024
Vendor
OAuth2 Proxy
Product
OAuth2 Proxy
Classifications
Unavailable
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Feb 2, 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

Compare your product and version with the public record. A matching version still requires validation against your environment.

Is a vulnerable build present?

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

  1. Affected versionversion=< 7.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OAuth2 Proxy · OAuth2 Proxyversion=< 7.0.0

Published CVSS scores

4.7CVE ProgramCVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/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

No sourced classifications are available.

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

See the directory against your own environment.

Your stack

Check the software in your environment

Book a demo to see how Hinoki identifies affected software and validates exploitability in your environment.

Book a demo