CVE-2020-4037Public exploitNetwork attack vector

Open redirect via incomplete redirect pattern validation

Published Jun 29, 2020 · Updated Aug 4, 2024

Open redirect in OAuth2 Proxy 5.1.1 through versions before 6.0.0 allows remote attackers to redirect authenticated users to harmful sites. The IsValidRedirect regular expression rejects only a narrow leading-slash pattern, so crafted values with repeated whitespace or dot segments between slash characters pass validation before browser normalization. Exploitation requires a user to follow an attacker-supplied link and complete the OAuth authentication flow, after which the proxy sends that user away from the intended application.

CVSS severity6.1
Medium
EPSS probability0.90%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Open redirect in OAuth2 Proxy 5.1.1 through versions before 6.0.0 allows remote attackers to redirect authenticated users to harmful sites. The IsValidRedirect regular expression rejects only a narrow leading-slash pattern, so crafted values with repeated whitespace or dot segments between slash characters pass validation before browser normalization. Exploitation requires a user to follow an attacker-supplied link and complete the OAuth authentication flow, after which the proxy sends that user away from the intended application.

The record

CVE
CVE-2020-4037
Published
Jun 29, 2020
Updated
Aug 4, 2024
Vendor
OAuth2 Proxy
Product
OAuth2 Proxy
Classifications
CWE-601, T1204.001
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jun 29, 2020CVE 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=>= 5.1.1, < 6.0.0

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OAuth2 Proxy · OAuth2 Proxyversion=>= 5.1.1, < 6.0.0

Published CVSS scores

6.1NISTCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:N
5.8NISTAV:N/AC:M/Au:N/C:P/I:P/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.

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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 exploitPublished

Weakness, pattern, technique

CWE-601URL Redirection to Untrusted Site ('Open Redirect')
T1204.001Malicious Link

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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