CVE-2026-40303

Summary
endpoints.GetSessionCookie parses an attacker-supplied cookie chunk count and calls make([]string, count) with no upper bound before any token validation occurs. The function is reached on every request to an OAuth-protected proxy share, allowing an unauthenticated remote attacker to trigger gigabyte-scale heap allocations per request, leading to process-level OOM termination or repeated goroutine panics. Both publicProxy and dynamicProxy are affected.

• Attack Vector: Network, exploitable via a single HTTP request with a crafted Cookie header.
• Attack Complexity: Low, no preconditions or chaining required; the attacker only needs to know the cookie name (publicly derivable from any OAuth redirect).
• Privileges Required: None, reached before JWT validation or any authentication check.
• User Interaction: None.
• Scope: Unchanged, impact is confined to the affected proxy process.
• Confidentiality Impact: None.
• Integrity Impact: None.

Availability Impact: High, sustained or concurrent requests cause OOM process termination, taking down the proxy for all users of all shares it serves.

Affected Components

• endpoints/oauthCookies.go, GetSessionCookie (line 81)
• endpoints/publicProxy/authOAuth.go, handleOAuth (line 50), call site, pre-auth
• endpoints/dynamicProxy/cookies.go, getSessionCookie (line 29), call site

Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service. Typical impact: denial of service.

CVE-2026-40303 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.0.1); upgrading removes the vulnerable code path.

Kodem intelligence

1. What is CVE-2026-40303? CVE-2026-40303 is a high-severity uncontrolled resource consumption vulnerability in github.com/openziti/zrok (go), affecting versions <= 1.1.11. It is fixed in 2.0.1. Crafted input forces the application to consume excessive CPU, memory, or other resources, degrading or denying service.
2. How severe is CVE-2026-40303? CVE-2026-40303 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
3. Which packages are affected by CVE-2026-40303?
   • github.com/openziti/zrok (go) (versions <= 1.1.11)
   • github.com/openziti/zrok/v2 (go) (versions < 2.0.1)
4. Is there a fix for CVE-2026-40303? Yes. CVE-2026-40303 is fixed in 2.0.1. Upgrade to this version or later.
5. Is CVE-2026-40303 exploitable, and should I be worried? Whether CVE-2026-40303 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
6. What actually determines whether CVE-2026-40303 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
7. How do I fix CVE-2026-40303? Upgrade github.com/openziti/zrok/v2 to 2.0.1 or later.