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

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.

Published: 2026-04-17 Last update: 2026-06-17 Assigner: [email protected] Source: [email protected]
NVD Status：Analyzed，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2026-40303 is rated Moderate Risk (42.9/100): CVSS High severity, with low exploitation likelihood (EPSS 0.45%). Review affected assets and schedule remediation.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2026-40303

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-06-15 0.02% 0.45% +0.43%
2 2026-04-21 0.06% 0.02% -0.03%
3 2026-04-18 — 0.06% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2026-40303

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
7.5 3.1 HIGH
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:N)
Could be attacked over the internet or any normal routed network—not just someone sitting at the machine.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:N)
No account or special rights needed—anonymous or random user is enough.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 3.9 3.6 [email protected]

Weakness enumeration for CVE-2026-40303

GitHub Security Advisory for CVE-2026-40303

GHSA-cpf9-ph2j-ccr9 · Severity: high · Ecosystem: go — zrok: Unauthenticated DoS via unbounded memory allocation in striped session cookie parsing

Affected software / configurations for CVE-2026-40303

Vendor Product Version Raw CPE
netfoundry zrok < 2.0.1 cpe:2.3:a:netfoundry:zrok:*:*:*:*:*:*:*:*

References for CVE-2026-40303

cvelogic Threat Intelligence