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    ArchLinux: 202012-18: nsd: denial of service

    Date 17 Dec 2020
    186
    Posted By LinuxSecurity Advisories
    The package nsd before version 4.3.4-1 is vulnerable to denial of service.
    Arch Linux Security Advisory ASA-202012-18
    ==========================================
    
    Severity: Low
    Date    : 2020-12-09
    CVE-ID  : CVE-2020-28935
    Package : nsd
    Type    : denial of service
    Remote  : No
    Link    : https://security.archlinux.org/AVG-1327
    
    Summary
    =======
    
    The package nsd before version 4.3.4-1 is vulnerable to denial of
    service.
    
    Resolution
    ==========
    
    Upgrade to 4.3.4-1.
    
    # pacman -Syu "nsd>=4.3.4-1"
    
    The problem has been fixed upstream in version 4.3.4.
    
    Workaround
    ==========
    
    None.
    
    Description
    ===========
    
    NLnet Labs Unbound, up to and including version 1.12.0, and NLnet Labs
    NSD, up to and including version 4.3.3, contain a local vulnerability
    that would allow for a local symlink attack. When writing the PID file,
    Unbound and NSD create the file if it is not there, or open an existing
    file for writing. In case the file was already present, they would
    follow symlinks if the file happened to be a symlink instead of a
    regular file.
    
    An additional chown of the file would then take place after it was
    written, making the user Unbound/NSD is supposed to run as the new
    owner of the file.
    
    If an attacker has local access to the user Unbound/NSD runs as, she
    could create a symlink in place of the PID file pointing to a file that
    she would like to erase. If then Unbound/NSD is killed and the PID file
    is not cleared, upon restarting with root privileges, Unbound/NSD will
    rewrite any file pointed at by the symlink.
    
    This is a local vulnerability that could create a Denial of Service of
    the system Unbound/NSD is running on. It requires an attacker having
    access to the limited permission user Unbound/NSD runs as and point
    through the symlink to a critical file on the system.
    
    Impact
    ======
    
    A local attacker might be able to cause a denial of service of the
    host.
    
    References
    ==========
    
    https://www.nlnetlabs.nl/downloads/unbound/CVE-2020-28935.txt
    https://github.com/NLnetLabs/unbound/issues/303
    https://nlnetlabs.nl/downloads/unbound/patch_cve-2020-28935_unbound.diff
    https://github.com/NLnetLabs/unbound/commit/ad387832979b6ce4c93f64fe706301cd7d034e87
    https://github.com/NLnetLabs/unbound/commit/19f8f4d9f99a44906ab9dcc46d44da299fde3506
    https://nlnetlabs.nl/downloads/nsd/patch_cve-2020-28935_nsd.diff
    https://github.com/NLnetLabs/nsd/commit/a4caec3137a1bc9eca05d38d66e2bce572ca9bd3
    https://security.archlinux.org/CVE-2020-28935
    

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