CVE-2021-32786Public exploitNetwork attack vector

Open redirect via backslash URL parser mismatch

Published Jul 22, 2021 · Updated Aug 3, 2024

Open redirect in OpenIDC mod_auth_openidc before 2.4.9 allows remote attackers to send users to an attacker-controlled site via logout. The oidc_validate_redirect_url function passed backslashes into APR URL parsing unchanged, while browsers treated them as path separators. Exploitation requires a user to follow a crafted logout URL, after which the trusted site redirects the browser to an attacker-controlled destination.

CVSS severity6.1
Medium
EPSS probability2.36%
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 OpenIDC mod_auth_openidc before 2.4.9 allows remote attackers to send users to an attacker-controlled site via logout. The oidc_validate_redirect_url function passed backslashes into APR URL parsing unchanged, while browsers treated them as path separators. Exploitation requires a user to follow a crafted logout URL, after which the trusted site redirects the browser to an attacker-controlled destination.

The record

CVE
CVE-2021-32786
Published
Jul 22, 2021
Updated
Aug 3, 2024
Vendor
OpenIDC
Product
mod_auth_openidc
Classifications
CWE-601, T1566.002
Attack vector
network
Privileges
unauthenticated

Timeline

How it unfolded

  1. Jul 22, 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=< 2.4.9

What conditions does exploitation require?

Attack vectornetwork
Required privilegesunauthenticated

What is affected?

OpenIDC · mod_auth_openidcversion=< 2.4.9

Published CVSS scores

6.1NVDCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
5.8NVDAV:N/AC:M/Au:N/C:P/I:P/A:N
4.7GitHub, Inc.CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:N/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.

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No observations available

Sep 9, 2026Sep 15, 2026
Latest reporting daySep 15, 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')
T1566.002Spearphishing 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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