Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-76835 – Authentication Bypass – oauth2-proxy 7.15.2–7.15.4

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-76835 is a critical authentication bypass vulnerability (CWE-290: Authentication Bypass by Spoofing) affecting oauth2-proxy, an open-source reverse proxy that authenticates requests via OAuth2/OIDC providers. It allows an unauthenticated attacker to reach a protected upstream path by spoofing the X-Forwarded-Uri header so it matches an allow-listed (skip-auth) route. The flaw carries a CVSS score of 9.3 (Critical) and represents an incomplete fix for the earlier advisory GHSA-7×63-xv5r-3p2x (CVE-2026-40575).

Technical details

  • Root cause: In --reverse-proxy mode, oauth2-proxy evaluates its skip_auth_routes/skip_auth_regex allow-list against the client-supplied X-Forwarded-Uri header rather than the actual request path, whenever the requesting source is considered a "trusted proxy."
  • Trigger conditions: --reverse-proxy is enabled, at least one skip-auth rule is configured, and --trusted-proxy-ip is left unset — in which case oauth2-proxy falls back to a default trusted-proxy set of 0.0.0.0/0 and ::/0, meaning every client is treated as trusted.
  • Attack vector: Network, unauthenticated, low complexity — an attacker simply sends a request to a protected path while setting X-Forwarded-Uri to a value matching a skip-auth route.
  • Impact: The auth check passes based on the spoofed header, while the real, protected path is forwarded unchanged to the upstream application, resulting in unauthorized access to protected resources (high confidentiality and integrity impact).

Affected software

  • oauth2-proxy versions 7.15.2 through 7.15.4, when deployed with --reverse-proxy and skip-auth rules, and with --trusted-proxy-ip left at its default/unset value.

Severity

  • CVSS v3.1 Base Score: 9.1 (Critical), consistent with the closely related predecessor issue; the CVE record for this specific issue is rated 9.3 (Critical) under CVSS v4.0 (AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:N/SC:N/SI:N/SA:N).

Mitigation and recommended actions

  • Immediate: No dedicated patched release beyond v7.15.4 has been confirmed at this time; monitor the oauth2-proxy GitHub repository/release notes for a fix that hardens the default trusted-proxy behavior and upgrade as soon as it is available.
  • Workarounds:
    • Explicitly configure --trusted-proxy-ip to a restrictive set of legitimate proxy IP ranges rather than leaving it unset.
    • Strip or overwrite any client-supplied X-Forwarded-Uri header at the load balancer/edge before it reaches oauth2-proxy.
    • Minimize or eliminate --skip-auth-route/--skip-auth-regex rules where feasible.
    • Restrict direct client access to oauth2-proxy so it is only reachable through trusted reverse proxies.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge