Sass LibSass Parsing Component Denial of Service Vulnerability [CVE-2018-20821]

CVE Number – CVE-2018-20821

A vulnerability in the parsing component of Sass LibSass could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition on a targeted system.

The vulnerability exists in the Sass::Parser::parse_css_variable_value function, as defined in the parser.cpp source code file, and is due to the affected software performing improper memory operations. An attacker could exploit this vulnerability by persuading a user to access a file that submits malicious input to the targeted system. A successful exploit could result in a DoS condition.Proof-of-concept (PoC) code that demonstrates an exploit of this vulnerability is publicly available.Sass has confirmed the vulnerability and released software updates.

Analysis

  • To exploit this vulnerability, the attacker may use misleading language or instructions to persuade a user to access a file that submits malicious input to the targeted system.

Safeguards

  • Administrators are advised to apply the appropriate updates.

    Administrators are advised to allow only trusted users to have network access.

    Administrators are advised to use an unprivileged account when browsing the Internet.

    Administrators are advised to monitor critical systems.

    Users are advised not to open email messages from suspicious or unrecognized sources. If users cannot verify that links or attachments included in email messages are safe, they are advised not to open them.

    Users are advised not to visit websites or follow links that have suspicious characteristics or cannot be verified as safe.

Vendor Announcements

  • Sass has released an issue report at the following link: Issue #2658

Fixed Software

Duncan Newell

Duncan is a technology professional with over 20 years experience of working in various IT roles. He has a interest in cyber security, and has a wide range of other skills in radio, electronics and telecommunications.

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