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CVE-2019-12735

Description

It was found that the :source! command was not restricted by the sandbox mode. If modeline was explicitly enabled, opening a specially crafted text file in vim could result in arbitrary command execution.

Statement

To be successfully and automatically triggered when a specially crafted file is opened, this vulnerability requires 3 parts :

  1. The source! command inability to check if it is running in sandbox mode (the fix commit prevents this)

  2. The modeline to be enabled (by default, modeline is disabled when running with root permission. See Mitigation steps to disable the modeline)

  3. A function, to be inserted in the modeline, that can be used to trigger the source! command (e.g.: assert_fail() in the public reproducer). To the best of our knowledge, no such functions were found in the default installation of Red Hat Enterprise Linux versions 5, 6 and 7 at the time of the flaw. However, Red Hat Enterprise Linux version 8 contains assert_fail().

Without part 2 or 3, it would be required for an attacker to be able to craft the command line used to open the crafted file, in order to trigger the vulnerability.

Mitigation

The vulnerability can be triggered only if `modeline` is enabled. You can check whether `modeline` is enabled within vim via the command `:set modeline?`
It can be turned off explicitly by adding `set nomodeline` in a vimrc file.

Common Vulnerability Scoring System (CVSS) Score Details

Info alert:Important note

CVSS scores for open source components depend on vendor-specific factors (e.g. version or build chain). Therefore, Red Hat's score and impact rating can be different from NVD and other vendors. Red Hat remains the authoritative CVE Naming Authority (CNA) source for its products and services (see Red Hat classifications).

CVSS v3 Score Breakdown

Red HatNVDcve.org
Base Score5.38.6N/A
Attack VectorLocalLocalN/A
Attack ComplexityLowLowN/A
Privileges RequiredNoneNoneN/A
User InteractionRequiredRequiredN/A
ScopeUnchangedChangedN/A
ConfidentialityLowHighN/A
Integrity ImpactLowHighN/A
Availability ImpactLowHighN/A

Vector

Red Hat: CVSS:3.1/AV:L/AC:L/PR:N/UI:R/S:U/C:L/I:L/A:L

NVD: CVSS:3.0/AV:L/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:H

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