Not ratedosv:RUSTSEC-2026-0425

    `nix-nar`: `Decoder::unpack` writes archive entries outside the destination directory (path traversal)

    Published Sources: OSV

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    Priority

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    CVSS v3

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    Severity
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    Priority (0–325)

    The priority score is a consolidated metric that condenses several individual signals into a single, action-guiding ranking: technical severity (CVSS), exploitation likelihood (EPSS), known-exploited status (KEV) and the context of the affected asset. The aim is to answer the only truly important question in vulnerability management: what first?

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    30.00 Methodology
    Exploit maturity

    An exploit is code or a technique that specifically uses a concrete vulnerability to force unintended behaviour — such as executing code or escalating privileges. It is the tool that turns a theoretical flaw into a practical attack.

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    no public PoC known
    KEV status

    The KEV catalogue is a list maintained by the US authority CISA of vulnerabilities for which active exploitation in the wild has been confirmed. It answers not the question „how severe?“ but „is it already being attacked?“ — thereby sharply prioritising patching.

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    Published

    Classification under NIS2 and CRA

    Rule-based classification from exploitation status and severity. It does not replace a case-by-case assessment.

    NIS2

    NIS2 is EU Directive (EU) 2022/2555 to raise the level of cybersecurity across the Union. It substantially broadens obligations compared with the first NIS directive: more sectors, mandatory risk management, staged reporting duties and personal accountability of senior management.

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    Handle the vulnerability in regular vulnerability handling under Art. 21(2)(e) NIS2.
    CRA

    The CRA is EU Regulation (EU) 2024/2847 setting horizontal cybersecurity requirements for „products with digital elements“ — from industrial controllers and software to connected consumer devices. For the first time manufacturers must ensure security across the entire product lifecycle, handle vulnerabilities and provide security updates.

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    From 11.12.2027, Annex I Part II CRA requires manufacturers of affected products with digital elements to handle vulnerabilities without delay and provide security updates.
    ISO/IEC 27001

    ISO/IEC 27001 is the internationally leading standard for an information security management system (ISMS). It describes a risk-based, process-oriented framework to systematically plan, implement, review and improve information security.

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    Control A.8.8, management of technical vulnerabilities: assess relevance to your systems, plan remediation and keep evidence.

    Description

    Decoder::unpack does not safely contain the paths it extracts, so a malicious NAR archive can create files outside the destination directory — a path traversal (CWE-22).

    In src/dec.rs (Decoder::unpack):

    • A symlink entry's target is written without checking where it points (src/dec.rs:153), so the archive can create a symlink that escapes the destination directory.
    • The out-of-destination containment check compares path strings only and does not account for symlinks created earlier in the same unpack (src/dec.rs:176-181), before reaching the write sinks (std::fs::create_dir at src/dec.rs:201 and OpenOptions::open at src/dec.rs:218).
    • The parser also accepts entry names containing / (src/parser.rs:138-147).

    Combined, a malicious archive can include a symlink a pointing at an external directory and then an entry named a/b, causing b to be written to <external>/b, outside the destination. This can create new files anywhere the process can write (it cannot overwrite existing files), which is escalatable to code execution by planting files in attacker-chosen locations.

    Source: OSV (Open Source Vulnerabilities)