zrok: Unauthenticated DoS via unbounded memory allocation in striped session cookie parsing

Exploitation

No confirmed exploitation recorded. Patch Next marks exploitation only from CISA KEV.

CVSS

7.5 · CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

EPSS

• CVE-2026-40303: 0.45% estimated exploitation activity in the next 30 days; percentile 39.36 (FIRST EPSS, 2026-11-03). This is a model estimate, not proof of exploitation or customer exposure.

As published by the source; long descriptions are shortened.

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 —…

Published by the source

16 Apr 2026, 21:09 UTC

Last modified by the source

24 Apr 2026, 20:48 UTC

Source last checked

26 Oct 2026, 15:19 UTC

1. Revision 1 · created · 26 Oct 2026

   Published from ghsa record GHSA-cpf9-ph2j-ccr9

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# Patch Next advisory brief: CVE-2026-40303

Advisory: zrok: Unauthenticated DoS via unbounded memory allocation in striped session cookie parsing
IDs: CVE-2026-40303, GHSA-cpf9-ph2j-ccr9
Record: https://patchnext.com/advisories/cve-2026-40303 (revision 1, source checked 26 Oct 2026, 15:19 UTC)
Inventory: none attached. This brief comes from a public page and does not say whether any deployment is affected.
Severity: High (CVSS 7.5)
Exploitation: no confirmed exploitation recorded. Patch Next confirms exploitation only from CISA KEV.
Vendor response: Partial vendor fix; fixed versions by package: github.com/openziti/zrok/v2 2.0.1. A vendor fix does not mean a deployment is fixed.

## Affected components
- Go github.com/openziti/zrok: affected <= 1.1.11
- Go github.com/openziti/zrok/v2: affected < 2.0.1; fixed in 2.0.1

## Suggested inspection (read-only)
- Go github.com/openziti/zrok: check the installed version with your package manager.
- Go github.com/openziti/zrok/v2: check the installed version with your package manager.

## Supported action
No complete vendor fix is recorded. Follow the primary source's mitigation guidance and check this record again before closing anything.

## Required regression checks
- Run the test suite and a production build.
- Exercise the features that depend on github.com/openziti/zrok, github.com/openziti/zrok/v2.
- Repeat the inspection and confirm that only fixed versions remain installed.

## Rollback considerations
- Keep the previous lockfile and deployment artifact. Rolling back reinstates the vulnerable version, so apply any documented mitigation while you fix forward.

## Unresolved questions
- Which deployments run an affected version?
- Exploitation status can change. Check again before lowering the priority.
- Mark the work resolved only after the fixed version is verified in production.

## Sources
- Verified: https://github.com/advisories/GHSA-cpf9-ph2j-ccr9 (GitHub-reviewed advisory GHSA-cpf9-ph2j-ccr9 lists affected ranges: Go github.com/openziti/zrok >=0 =0 <2.0.1)

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