CVE-2026-40575 — OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing
OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application. This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client.
Who exploits it and how urgent it is
A 0–100 score combining confirmed exploitation, ransomware and APT use, public exploits, EPSS and severity.
How the score was calculated
- EPSS 0.7% (30-day exploitation probability)+8
- Technical severity (critical)+10
- Automatable exploitation (SSVC)+3
The score orders the patch queue; it does not replace your asset context (internet exposure, criticality, compensating controls).
Triage
Is it exploited, how likely is exploitation, what does it touch, and how severe do the sources call it.
CISA SSVC assessment CISA
Three decision points CISA publishes for the CVEs it assesses (SSVC 2.0.3). A stakeholder decision, not a severity score.
Remediation
Fixes and mitigations documented by the sources — linked to the original advisory.
- Go Github.com/oauth2-proxy/oauth2-proxy/v7: fixed in version 7.15.2 — github.com (GitHub Security Advisories)
First 24 hours
Ordered from the record’s own fields — exposure first, because you cannot patch what you have not found. A rule-generated starting point.
- Identify exposed assets running the affected vendor/product/version combinations (Oauth2 Proxy Project Oauth2 Proxy, Oauth2-proxy Oauth2-proxy, Go Github.com/oauth2-proxy/oauth2-proxy/v7).
- The attack is network-based and needs no privileges: restrict exposure (ACLs, VPN, WAF) until patched.
- Apply the fixed version or the patch documented under Remediation.
- Search available logs for exploit probes matching the vulnerability class (authentication), errors and authentication anomalies.
Affected scope
Vendor, product and versions as the sources word them.
| Vendor | Product | Versions | Status | Source |
|---|---|---|---|---|
| Oauth2 Proxy Project | Oauth2 Proxy | ≥ 7.5.0 and < 7.15.2 | Vulnerable | NIST National Vulnerability Database |
| Oauth2-proxy | Oauth2-proxy | version >= 7.5.0, < 7.15.2 | Vulnerable | CVE Program (cve.org) e CISA ADP |
| Go | Github.com/oauth2-proxy/oauth2-proxy/v7 | ≥ 7.5.0 and < 7.15.2 | Vulnerable | GitHub Security Advisories |
Attack characteristics
The CVSS vector, decoded. It describes the attack, not your exposure to it.
Every base score collected
Sources score independently and may disagree; each row says who scored it and under which version.
| Score | Version | Severity | Expl. | Impact | Scored by |
|---|---|---|---|---|---|
| 9.1 | CVSS 3.1 | Critical | 3.9 | 5.2 | security-advisories@github.com via NIST National Vulnerability Database |
| 9.1 | CVSS 3.1 | Critical | — | — | GitHub, Inc. via GitHub Security Advisories |
| 9.1 | CVSS 3.1 | Critical | — | — | GitHub_M via CVE Program (cve.org) e CISA ADP |
| 8.7 | CVSS 3.1 | High | 2.2 | 5.8 | 0b0ca135-0b70-47e7-9f44-1890c2a1c46c via NIST National Vulnerability Database |
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N (score shown at the top: security-advisories@github.com) Weakness MITRE
Weakness class according to MITRE’s CWE catalog.
EPSS over time FIRST
Oct 13, 2026 → Oct 14, 2026 · 2 reading(s) · max 0.73%
Detection
Read off the CVSS vector and the weakness class. Starting points, not tested rules.
- Prioritize edge telemetry for the network-reachable component (proxy, WAF, IDS/IPS).
- Review authentication logs: logins without MFA, anomalous sessions and recently created accounts.
Timeline
What happened to this CVE, newest first.
- 2026
- Fix documented
- Affected products added · go/github.com/oauth2-proxy/oauth2-proxy/v7
- Affected products added · oauth2-proxy/oauth2-proxy
- SSVC assessment updated
- Record published
- CVSS changed · 9.1
- Source status changed · → Modified
- Record created in this database
- CVE published
Source activity
Repeated readings are counted rather than listed.
- 1× References added · Oct 13, 2026 – Oct 13, 2026
- 1× Official description updated · Oct 13, 2026 – Oct 13, 2026
References
6 on the record
- github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x
- github.com/advisories/GHSA-7x63-xv5r-3p2x
- bugzilla.redhat.com/show_bug.cgi
- access.redhat.com/security/cve/CVE-2026-40575
- nvd.nist.gov/vuln/detail/CVE-2026-40575
- security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-40575.json
Elsewhere on this site
Related CVEs (same products)
- Critical CVE-2026-76835 OAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy Set Aug 24, 2026
- High CVE-2026-41059 OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex Apr 21, 2026
- Medium CVE-2026-40574 OAuth2 Proxy has an Authorization Bypass in Email Domain Validation via Malformed Multi-@ Email Claims Apr 21, 2026
- Low CVE-2026-34454 OAuth2 Proxy: Session cookie not cleared when rendering sign-in page Apr 14, 2026
- Critical CVE-2026-34457 OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode Apr 14, 2026
- High CVE-2025-64484 OAuth2-Proxy vulnerable to header smuggling via underscore, leading to potential privilege escalation Nov 10, 2025
Not in any source we poll
Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.
- No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
- No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
- No exploit packet captures, log samples, or incident case IDs supplied.
Answered from this record
Text assembled only from the fields above — no additional claims.
What should defenders know first?
CVE-2026-40575 is "OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing", rated Critical. It affects Oauth2 Proxy (Oauth2 Proxy Project); versions are in the scope table. It is not in CISA KEV, which does not rule out exploitation. CVSS 9.1 describes technical severity. EPSS 0.73% estimates the probability of exploitation in 30 days; neither replaces your asset context. First verify whether exposed or business-critical assets run the affected versions, apply vendor fixes or mitigations, and preserve logs for review.
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