CVE-2021-3847

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DescriptionMitigationAdditional informationAffected PackagesCVSS Score DetailsWeakness (CWE)AcknowledgementsFAQ

Description

An unauthorized access to the execution of the setuid file with capabilities flaw in the Linux kernel OverlayFS subsystem was found in the way user copying a file with capabilities from a nosuid mount into another mount. A local user could use this flaw to escalate their privileges on the system.

An unauthorized access to the execution of the setuid file with capabilities flaw in the Linux kernel OverlayFS subsystem was found in the way user copying a file with capabilities from a nosuid mount into another mount. A local user could use this flaw to escalate their privileges on the system.

Mitigation

The mitigation is to mount overlayfs with nosuid if lower layer is nosuid.

Additional information

  • Bugzilla 2009704: kernel: low-privileged user privileges escalation
  • CWE-281: Improper Preservation of Permissions
  • FAQ: Frequently asked questions about CVE-2021-3847

Common Vulnerability Scoring System (CVSS) Score Details

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).

The following CVSS metrics and score provided are preliminary and subject to review.

CVSS v3 Score Breakdown
Red HatNVD

CVSS v3 Base Score

6.7

7.8

Attack Vector

Local

Local

Attack Complexity

Low

Low

Privileges Required

High

Low

User Interaction

None

None

Scope

Unchanged

Unchanged

Confidentiality Impact

High

High

Integrity Impact

High

High

Availability Impact

High

High

CVSS v3 Vector

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

NVD: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Red Hat CVSS v3 Score Explanation

The privileges required High (PR:H), because "mount: only root can use "--options" option" (so regular user cannot run command like "mount -t overlay overlay -o lowerdir=/lower,upperdir=/upper,workdir=/work /merged" if without root or some other root-like privileges). For the case when inserting USB device that this bug about unlikely that auto-mount could happen for OverlayFS too. However, there is other more or less similar CVE-2023-0386 about OverlayFS subsystem where actually PR:L.

The privileges required High (PR:H), because "mount: only root can use "--options" option" (so regular user cannot run command like "mount -t overlay overlay -o lowerdir=/lower,upperdir=/upper,workdir=/work /merged" if without root or some other root-like privileges). For the case when inserting USB device that this bug about unlikely that auto-mount could happen for OverlayFS too. However, there is other more or less similar CVE-2023-0386 about OverlayFS subsystem where actually PR:L.

Acknowledgements

Red Hat would like to thank Alon Zahavi (CyberArk) for reporting this issue.

Frequently Asked Questions

Why is Red Hat's CVSS v3 score or Impact different from other vendors?

For open source software shipped by multiple vendors, the CVSS base scores may vary for each vendor's version depending on the version they ship, how they ship it, the platform, and even how the software is compiled. This makes scoring of vulnerabilities difficult for third-party vulnerability databases such as NVD that only provide a single CVSS base score for each vulnerability. Red Hat scores reflect how a vulnerability affects our products specifically.

For more information, see https://access.redhat.com/solutions/762393.

My product is listed as "Under investigation" or "Affected", when will Red Hat release a fix for this vulnerability?

  • "Under investigation" doesn't necessarily mean that the product is affected by this vulnerability. It only means that our Analysis Team is still working on determining whether the product is affected and how it is affected.
  • The term "Affected" means that our Analysis team has determined that this product, such as Red Hat Enterprise Linux 8 or OpenShift Container Platform 4, is affected by this vulnerability and a fix may be released to address this issue in the near future. This includes all minor releases of this product unless noted otherwise in the Statement text.

What can I do if my product is listed as "Will not fix"?

A "will not fix" status means that a fix for an affected product version is not planned or not possible due to complexity, which may create additional risk.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Upgrade to a supported product version that includes a fix for this vulnerability (recommended).
  • Apply a mitigation (if one exists).
  • Open a support case to request a prioritization of releasing a fix for this vulnerability.

What can I do if my product is listed as "Fix deferred"?

A deferred status means that a fix for an affected product version is not guaranteed due to higher-priority development work.

Available options depend mostly on the Impact of the vulnerability and the current Life Cycle phase of your product. Overall, you have the following options:
  • Apply a mitigation (if one exists).
  • Open a support case to request a prioritization of releasing a fix for this vulnerability.
  • Red Hat Engineering focuses on addressing high-priority issues based on their complexity or limited lifecycle support. Therefore, lower-priority issues will not receive immediate fixes.

What is a mitigation?

A mitigation is an action that can be taken to reduce the impact of a security vulnerability, without deploying any fixes.

I have a Red Hat product but it is not in the above list, is it affected?

The listed products were found to include one or more of the components that this vulnerability affects. These products underwent a thorough evaluation to determine their affectedness by this vulnerability. Note that layered products (such as container-based offerings) that consume affected components from any of the products listed in this table may be affected and are not represented.

Why is my security scanner reporting my product as vulnerable to this vulnerability even though my product version is fixed or not affected?

In order to maintain code stability and compatibility, Red Hat usually does not rebase packages to entirely new versions. Instead, we backport fixes and new features to an older version of the package we distribute. This can result in some security scanners that only consider the package version to report the package as vulnerable. To avoid this, we suggest that you use an approved vulnerability scanner from our Red Hat Vulnerability Scanner Certification program.

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