CVE-2026-34457: OAuth2 Proxy's Health Check User-Agent Matching Bypasses Authentication in auth_request Mode

Should you act?

Critical and remotely reachable

No known exploitation yet, but it is network-reachable without credentials. This signal is computed from CISA KEV, EPSS and CVSS data; it is not an editorial verdict.

• No confirmed exploitation. It is not in CISA’s KEV catalog and CISA’s SSVC assessment records no known exploitation. That can change quickly after a public write-up; re-check if you are affected.
• EPSS 0.7%, percentile 51: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 51% of all scored CVEs (moderate). EPSS is a probability, not a verdict.
• Remotely reachable with no login and no user interaction. If the vulnerable service is exposed to the internet, prioritize it.
• Only applies if your dependency tree includes github.com/oauth2-proxy/oauth2-proxy/v7 (Go) < 7.15.2, fixed in 7.15.2; github.com/oauth2-proxy/oauth2-proxy (Go) <= 3.2.0, no fixed version listed. Check your lockfile, including transitive dependencies.

What it is

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions prior to 7.15.2 contain a configuration-dependent authentication bypass in deployments where OAuth2 Proxy is used with an authrequest-style integration (such as nginx authrequest) and either --ping-user-agent is set or --gcp-healthchecks is enabled. In affected configurations, OAuth2 Proxy treats any request with the configured health check User-Agent value as a successful health check regardless of the requested path, allowing an unauthenticated remote attacker to bypass authentication and access protected upstream resources. Deployments that do not use authrequest-style subrequests or that do not enable --ping-user-agent/--gcp-healthchecks are not affected. This issue is fixed in 7.15.2.

From the GitHub advisory

Impact A configuration-dependent authentication bypass exists in OAuth2 Proxy.

Deployments are affected when all of the following are true:

- OAuth2 Proxy is used with an authrequest-style integration (for example, nginx authrequest) - --ping-user-agent is set or --gcp-healthchecks is enabled

In affected configurations, OAuth2 Proxy will treat a request with the configured health check User-Agent value as a successful health check regardless of the requested path. This allows an unauthenticated remote attacker to bypass authentication and access protected upstream resources without completing the normal login flow.

This issue does not affect deployments that do not use authrequest-style subrequests, or that do not enable --ping-user-agent/--gcp-healthchecks.

Weakness type: CWE-290.

Product: github.com/oauth2-proxy/oauth2-proxy/v7 (Go) · Assigned by: GitHub_M · Published: 2026-04-14

Affected and fixed versions

Severity scores

• Attack vector: network (remotely reachable)
• Attack complexity: low
• Privileges required: none (no login)
• User interaction: none
• Scope: unchanged

CVSS measures how bad a flaw is if exploited, not how likely exploitation is. Read it next to the exploitation data below.

Exploitation and urgency

• CISA KEV: not listed (no confirmed in-the-wild exploitation known to CISA).
• CISA SSVC assessment: exploitation none, automatable yes, technical impact total.
• FIRST EPSS (model of 2026-10-21): 0.66% probability of exploitation activity in the next 30 days; percentile 51.

Timeline

• 2026-04-14 — CVE record published by GitHub_M
• 2026-04-14 — GitHub-reviewed advisory GHSA-5hvv-m4w4-gf6v published (critical)
• 2026-04-15 — CVE record last updated

Sources and references

Original sources first. Version and fix details should always be confirmed against the vendor or project advisory.

Vulnerability records

1. GitHub Advisory GHSA-5hvv-m4w4-gf6v github.com
2. CVE.org record CVE-2026-34457 cve.org
3. NVD entry CVE-2026-34457 nvd.nist.gov

Other references from the CVE record and advisory

1. github.com github.com
2. github.com github.com

Critical Go advisories · Today’s Security Digest