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MEDIUM severity

OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email ClaimsGHSA-c5c4-8r6x-56w3

MEDIUM

GHSA-c5c4-8r6x-56w3 is a medium-severity (CVSS 6.8) CWE-863 vulnerability in github.com/oauth2-proxy/oauth2-proxy/v7. A fix is available for github.com/oauth2-proxy/oauth2-proxy/v7 — see the affected versions and patch details below.

Also known asBIT-oauth2-proxy-2026-40574CVE-2026-40574GO-2026-5314
Published
Updated
Affected
1 pkg
Patched
1 / 1
Exploits
None indexed
Exploitation data as of Nov 3, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

  • A successful exploit gives an attacker total control of the affected component, not partial access.
  • CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for GHSA-c5c4-8r6x-56w3.

EPSS Exploitation Probability

via FIRST.org ↗
0.2%probability of exploitation in next 30 days
Lower Risk0.00%
Lower risk than most CVEs11th percentile — riskier than 11% of all scored CVEsHighest risk
0.00%0.28%0.56%0.84%0.0%0.2%May 26Sep 26Nov 26

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

1 pkg affected
🐹github.com/oauth2-proxy/oauth2-proxy/v7

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Go packages — download data is not available via public APIs for these ecosystems.

Description

Impact

An authorization bypass exists in OAuth2 Proxy as part of the email_domain enforcement option. An attacker may be able to authenticate with an email claim such as [email protected]@company.com and satisfy an allowed domain check for company.com, even though the claim is not a valid email address.

The issue ONLY affects deployments that rely on email_domain restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and federated setups where unexpected claim values can reach oauth2-proxy. Standard hosted providers that enforce valid email formatting ARE NOT effected.

Patches

Users should upgrade to v7.15.2 or later once available.

Workarounds

The most effective workaround is to ensure the configured identity provider cannot emit malformed or attacker-controlled email claim values.

Affected Packages

1 total 1 fixed
EcosystemPackageVulnerable rangeFix
🐹Gogithub.com/oauth2-proxy/oauth2-proxy/v7all versions7.15.2go get github.com/oauth2-proxy/oauth2-proxy/v7@v7.15.2

Affected Products

1 product · 1 configurations
Application
oauth2 proxyoauth2_proxy_project
< 7.15.2
range

Detection & mitigation playbook

Open-source dependency

  1. Detect

    Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for github.com/oauth2-proxy/oauth2-proxy/v7, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

  2. Fix

    Update github.com/oauth2-proxy/oauth2-proxy/v7 to 7.15.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms GHSA-c5c4-8r6x-56w3 is resolved across your whole dependency graph.

  3. Workarounds

    Put an independent control in front of the weakness: restrict the affected endpoint or interface to trusted networks, require an additional authentication factor or proxy-level check, and invalidate existing sessions and credentials in case the flaw has already been used.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatModerate

A Moderate impact authorization bypass flaw exists in OAuth2 Proxy affecting deployments configured with `email_domain` restrictions. This vulnerability allows a remote attacker to bypass these restrictions by crafting a malicious email claim, such as `[email protected]@company.com`, if the identity provider or claim…

Workaround published by Red Hat
To mitigate this issue, configure identity providers or claim mappings to strictly enforce normal email syntax for all email claim values. This prevents the acceptance of malformed email claims that could bypass `email_domain` restrictions. Red Hat recommends reviewing OAuth2 Proxy deployment configurations and associated identity providers to ensure robust email validation is in place.
Source: Red Hat security advisory for GHSA-c5c4-8r6x-56w3 (CC BY 4.0)

Frequently Asked Questions

### Impact An authorization bypass exists in OAuth2 Proxy as part of the `email_domain` enforcement option. An attacker may be able to authenticate with an email claim such as `[email protected]@company.com` and satisfy an allowed domain check for `company.com`, even though the claim is not a valid email address. The issue **ONLY** affects deployments that rely on `email_domain` restrictions and accept email claim values from identity providers or claim mappings that do not strictly enforce normal email syntax. The practical risk ONLY exists in self-hosted or custom OIDC environments and fed
O3 Security · Impact-Aware SCA

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