CVE-2026-40303 zrok allows unauthenticated DoS via unbounded memory allocation in striped session cookie parsing
Unauthenticated attackers can cause denial of service in zrok by sending crafted cookies that trigger unbounded memory allocation, crashing the service.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40303?
CVE-2026-40303 is a high-severity denial of service vulnerability in openziti zrok, published on 17 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
zrok is software for sharing web services, files, and network resources. Prior to version 2.0.1, 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. Version 2.0.1 patches the issue.
Which versions are affected by CVE-2026-40303?
6 open source packages ship an affected version, including github.com/openziti/zrok and github.com/openziti/zrok/v2. It affects 1 product.
| Package | Affected | Fixed in |
|---|---|---|
github.com/openziti/zrok Go | All versions | None |
github.com/openziti/zrok Go | All versions to 1.1.11 | None |
github.com/openziti/zrok Go | All versions to 1.1.11 | None |
github.com/openziti/zrok/v2 Go | All versions | 2.0.1 |
github.com/openziti/zrok/v2 Go | All versions | 2.0.1 |
github.com/openziti/zrok/v2 Go | All versions | 2.0.1 |
Products include Netfoundry Zrok.
How do I fix CVE-2026-40303?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-40303 being exploited?
There is no known exploitation of CVE-2026-40303 in the wild and no public exploit code.
Other vulnerabilities in openziti zrok
- CVE-2026-45568 zrok Python ProxyShare can be used as an SSRF proxy through absolute URL paths
- CVE-2026-42275 zrok: WebDAV drive backend follows symlinks outside DriveRoot, enabling host filesystem read/write
- CVE-2026-45576 zrok copy writes attacker-controlled WebDAV paths outside the destination root
- CVE-2026-40302 zrok has reflected XSS in GitHub OAuth callback via unsanitized refreshInterval error rendering
- CVE-2026-40304 zrok's broken ownership check in DELETE /api/v2/unaccess allows non-admin to delete global frontend records
Sources
Also known as GHSA-cpf9-ph2j-ccr9, GO-2026-5329.