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 :
The
source!command inability to check if it is running in sandbox mode (the fix commit prevents this)The
modelineto be enabled (by default, modeline is disabled when running with root permission. SeeMitigationsteps to disable the modeline)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 containsassert_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 Hat | NVD | cve.org | |
|---|---|---|---|
| Base Score | 5.3 | 8.6 | N/A |
| Attack Vector | Local | Local | N/A |
| Attack Complexity | Low | Low | N/A |
| Privileges Required | None | None | N/A |
| User Interaction | Required | Required | N/A |
| Scope | Unchanged | Changed | N/A |
| Confidentiality | Low | High | N/A |
| Integrity Impact | Low | High | N/A |
| Availability Impact | Low | High | N/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
Understanding the Weakness (CWE)
Access Control
Technical Impact: Bypass Protection Mechanism
In some cases, injectable code controls authentication; this may lead to a remote vulnerability.
Access Control
Technical Impact: Gain Privileges or Assume Identity
Injected code can access resources that the attacker is directly prevented from accessing.
Integrity,Confidentiality,Availability
Technical Impact: Execute Unauthorized Code or Commands
When a product allows a user's input to contain code syntax, it might be possible for an attacker to craft the code in such a way that it will alter the intended control flow of the product. As a result, code injection can often result in the execution of arbitrary code. Code injection attacks can also lead to loss of data integrity in nearly all cases, since the control-plane data injected is always incidental to data recall or writing.
Non-Repudiation
Technical Impact: Hide Activities
Often the actions performed by injected control code are unlogged.
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