Security Digest · Vulnerability record
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.
CVSS 9.1 Critical EPSS 0.7% · p54
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 54: FIRST’s model estimates a 0.7% chance of exploitation activity in the next 30 days, higher than 54% 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) >= 7.5.0, < 7.15.2, fixed in 7.15.2. Check your lockfile, including transitive dependencies.
What it is
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.
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 configured with --reverse-proxy and at least one rule is defined with --skipauthroutes or the legacy --skip-auth-regex
OAuth2 Proxy may trust a client-supplied X-Forwarded-Uri header when --reverse-proxy is enabled and --skip-auth-route or --skip-auth-regex 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.
Weakness type: CWE-290.
Product: github.com/oauth2-proxy/oauth2-proxy/v7 (Go) · Assigned by: GitHub_M · Published: 2026-04-21
Affected and fixed versions
| Ecosystem | Package | Vulnerable | First fixed |
|---|---|---|---|
| Go | github.com/oauth2-proxy/oauth2-proxy/v7 | >= 7.5.0, < 7.15.2 | 7.15.2 |
| Vendor | Product | Affected versions (per CVE record) |
|---|---|---|
| oauth2-proxy | oauth2-proxy | >= 7.5.0, < 7.15.2 |
Severity scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_M | 3.1 | 9.1 Critical | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
| redhat-SADP | 3.1 | 8.7 High | CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:C/C:H/I:H/A:N |
| GitHub | 3.1 | 9.1 | CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N |
- 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): 0.73% probability of exploitation activity in the next 30 days; percentile 54.
Timeline
- — GitHub-reviewed advisory GHSA-7x63-xv5r-3p2x published (critical)
- — CVE record published by GitHub_M
- — 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
- GitHub Advisory GHSA-7x63-xv5r-3p2x github.com
- CVE.org record CVE-2026-40575 cve.org
- NVD entry CVE-2026-40575 nvd.nist.gov
Other references from the CVE record and advisory
- github.com github.com
- access.redhat.com access.redhat.com
- RHBZ#2460449 bugzilla.redhat.com
- security.access.redhat.com security.access.redhat.com