CVE-2026-40303
Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.
NVD · uneditedzrok 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.
Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.
dbcve analysis · high confidenceThe endpoints.GetSessionCookie function in zrok parses an attacker-supplied cookie chunk count value and passes it directly to make([]string, count) without any upper bound validation, allowing unauthenticated attackers to trigger gigabyte-scale heap allocations per request to OAuth-protected proxy shares, leading to OOM termination or goroutine panics.
Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.
Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.
NVD · CPE data< 2.0.1CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.
From the vector- Attack vector
- Network
- Complexity
- Low
- Privileges
- None
- User interaction
- None
- Scope
- Unchanged
- Confidentiality
- None
- Integrity
- None
- Availability
- High
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.
dbcve checksWork through these to decide whether this CVE applies to you.
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Identify zrok installation and versionRun 'zrok --version' or check the installed zrok binary version using your system's package manager (e.g., dpkg, rpm, brew) or by inspecting the binary directlyAffected if The installed version is lower than 2.0.1 (e.g., 2.0.0, 1.x.x, or any pre-2.0.1 release)
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Confirm the vulnerable code path is presentInspect the binary or source code for the endpoints.GetSessionCookie function and verify it uses make([]string, count) without bounds checking on the count parameterAffected if The GetSessionCookie function lacks upper bound validation on the cookie chunk count before calling make([]string, count)
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Determine if OAuth-protected proxy shares are configuredReview zrok configuration files (typically in /etc/zrok, ~/.zrok, or the directory where zrok configuration is stored) and check for proxy share definitions that reference OAuth authentication providersAffected if OAuth-protected proxy shares are enabled and exposed to unauthenticated network requests
You are affected if you have zrok version < 2.0.1 running with OAuth-protected proxy shares exposed to the network, as this allows unauthenticated heap exhaustion attacks.
Generated from the published advisory. Verify against your own configuration.
Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.
dbcve · scoped2.0.1
Upgrade to zrok version 2.0.1 or later which patches this vulnerability; until then, consider rate-limiting or temporarily disabling OAuth-protected proxy shares to mitigate unauthenticated heap exhaustion attacks.
2.0.1
- Upgrade zrok to version 2.0.1 or later
Generated from the published advisory — verify against the referenced sources before acting.
- Consultation2.0 h
- Implementation2.0 h
- Testing4.0 h
- Review / QA1.0 h
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Scan for this in your stack
Free · runs locallyCheck whether your project pulls in CVE-2026-40303 — or any other known-vulnerable package — straight from your lock files. Free and open source; it runs locally and uploads nothing.
References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.
Primary sourcesPractitioner notes
ContributedPeer-ranked notes from engineers who’ve handled CVE-2026-40303 in production — separate from our analysis above.
The advisory tells you what broke. It rarely tells you what actually worked. If you’ve dealt with this one, that detail is what the next engineer is searching for.
- The version that genuinely resolved it — not the one the vendor claimed
- A config change or rule that shut the vector down
- A gotcha in the upgrade path that cost you an afternoon
No notes yet
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- Version or environment caveats, and links to real fixes
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