EUVD-2026-100809
GHSA-cm63-px87-wf8p
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain local build-user context on unsandboxed Nix (macOS/FreeBSD)
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ExploitInitiate daemon connection as build user
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ExecutionDaemon incorrectly authorizes cross-boundary connection
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ImpactTamper with build/daemon trust boundary
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A01:2025 - Broken Access Control
ASVS 5.0
V8 - Authorization Authorization logic validation
MITRE ATT&CK
1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Requires Nix earlier than 2.35.3 running in unsandboxed mode specifically on macOS or FreeBSD, and the attacker must already operate as a Nix build user able to open a daemon client connection. LIMITING FACTORS: not exploitable remotely (local vector only); does not affect sandboxed deployments (notably Linux default sandboxed configurations); confined to the macOS/FreeBSD unsandboxed deployment mode; impact is limited to integrity with no confidentiality or availability effect. Defenders can mitigate by enabling sandboxing or upgrading to 2.35.3 or later. |
| Impact | This is a moderate, locally-scoped authorization flaw (CVSS 4.3) rather than a high-urgency priority. The provided CVSS vector is AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N: local attack vector (no network exploitation), low complexity, no confidentiality or availability impact, and only low integrity impact, offset by a changed scope reflecting that the flaw crosses the build-user/daemon trust boundary. There is no EPSS score provided, no CISA KEV listing, and no public exploit code referenced, so there is no public exploit identified at time of analysis and no evidence of active exploitation. Note a conflict between signals: the input CVSS encodes PR:N (unauthenticated), but the description - 'connections made by build users from daemon clients' - implies the actor must already be a local Nix build user, which is a privileged/local precondition; verify the privilege requirement with the vendor advisory. Exploitation is further gated to a specific configuration (unsandboxed Nix on macOS or FreeBSD), which materially narrows the exposed population below what the raw CVSS score suggests. |
| Exploit ScenarioDerived | On a macOS or FreeBSD system running Nix older than 2.35.3 with sandboxing disabled, a process running as a Nix build user initiates a connection to the Nix daemon that should have been rejected; the daemon incorrectly authorizes it, letting the build process act across the intended isolation boundary. No public exploit code is known, and the impact is limited to integrity (not data theft or denial of service). Exploitation requires local presence as a build user and the specific unsandboxed deployment. |
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Alert meAnalysisAIv1 – Oct 14, 2026
Nix releases before 2.35.3 in unsandboxed macOS or FreeBSD deployments permit a local authenticated build user to establish daemon client connections that should be denied, enabling unauthorized interactions with the Nix daemon. The independently assessed CVSS is 4.3 (CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N), reflecting a local, scope-changed authorization weakness with limited integrity impact and no confidentiality or availability impact. No public exploit identified at time of analysis; the issue is confined to unsandboxed macOS/FreeBSD configurations, and upgrading to 2.35.3 or enabling sandboxing removes the exposure.
RemediationAI
Vendor-released patch: 2.35.3. Upgrade Nix to 2.35.3 or later, per the vendor advisory at https://discourse.nixos.org/t/security-advisory-for-nix-and-lix-october-2026/80547. If immediate upgrade is not possible, enable sandboxing for the Nix daemon where supported, because the vulnerability only exists in unsandboxed macOS/FreeBSD deployments; the trade-off is that sandboxing can break builds requiring unsandboxed operations and may not be supported in all macOS/FreeBSD setups. As a compensating control, restrict build-user privileges and daemon client access to trusted local users, though this is operationally restrictive and does not fully fix the authorization bypass.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 1 package in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
Nix uses a privileged daemon (nix-daemon) to manage the store and execute builds, with unprivileged build users running build processes. The flaw is an Incorrect Authorization (CWE-863) condition in the daemon's client-connection handling when sandboxing is disabled on macOS or FreeBSD: build users can connect in a way that should be restricted to daemon clients, bypassing intended access controls for build operations. The affected CPE is cpe:2.3:a:nixos:nix:*:*:*:*:*:*:*:* for versions before 2.35.3, and the independent assessment's CVSS:3.1 vector (AV:L/AC:L/PR:L/UI:N/S:C/C:N/I:L/A:N) confirms the attacker must already be a local build user, with the scope change reflecting the authorization boundary crossing; sandboxed configurations and Linux default deployments are unaffected.
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Severity by source
AV:L/AC:L/PR:N/UI:N/S:C/C:N/I:L/A:N
Local-only and requires an existing build-user context so PR:L (not PR:N); scope changes as the build user crosses into the daemon trust boundary; integrity-only, no confidentiality or availability impact.
Primary rating from Vendor (mitre).
CVSS VectorVendor: mitre
Lifecycle Timeline
2DescriptionCVE.org
Nix before 2.35.3, when unsandboxed on macOS or FreeBSD, incorrectly allows connections made by build users from daemon clients.
Threat Intelligence Overview
NVD
CVE.org
EPSS
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
Authentication bypass attacks exploit flaws in the verification mechanisms that control access to systems and applications.
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Exploit-DB