CVE-2021-33910

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Important Important Impact What does this mean?
5.5 CVSS v3 Base Score

Description

A flaw was found in systemd. The use of alloca function with an uncontrolled size in function unit_name_path_escape allows a local attacker, able to mount a filesystem on a very long path, to crash systemd and the whole system by allocating a very large space in the stack. The highest threat from this vulnerability is to the system availability.

Statement

This issue did not affect the versions of systemd as shipped with Red Hat Enterprise Linux 7 as they did not use strdupa to duplicate strings in unit_name_path_escape function, but strdup, which allocates space on the heap.

Further, any Red Hat product which is supported on the Red Hat Enterprise Linux platform is also potentially impacted. This includes:

  • Product containers which are based on the RHEL or UBI container images. These images are updated regularly, and container health indicating whether a fix to this flaw is available can be seen in the Container Health Index, part of the Red Hat Container Catalog (This content is not included.https://access.redhat.com/containers). In addition, any customer containers should be manually rebuilt when the base images are updated.
  • Products which pull packages from the RHEL channel. Please ensure that the underlying Red Hat Enterprise Linux systemd package is current in these product environments.

Mitigation

Red Hat has investigated whether a possible mitigation exists for this issue, and has not been able to identify a practical example. Please update as soon as possible.

Additional Information

External References

Content from www.cve.org is not included.https://www.cve.org/CVERecord?id=CVE-2021-33910

Content from nvd.nist.gov is not included.https://nvd.nist.gov/vuln/detail/CVE-2021-33910

Content from www.qualys.com is not included.https://www.qualys.com/2021/07/20/cve-2021-33910/denial-of-service-systemd.txt

Affected Packages and Issued Red Hat Security Errata

Products / Services Components State Errata
Red Hat Enterprise Linux 7 systemd Not affected
Red Hat Enterprise Linux 8 systemd Fixed RHSA-2021:2717
Red Hat Enterprise Linux 8.1 Extended Update Support systemd Fixed RHSA-2021:2724
Red Hat Enterprise Linux 8.2 Extended Update Support systemd Fixed RHSA-2021:2721
Red Hat Enterprise Linux 9 systemd Not affected
Red Hat Virtualization 4 for Red Hat Enterprise Linux 8 redhat-virtualization-host Fixed RHSA-2021:2736
Unless explicitly stated as not affected, all previous versions of packages in any minor update stream of a product listed here should be assumed vulnerable, although may not have been subject to full analysis.

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 Authorities (CNA) source for its products and services (see Red Hat classifications ).

CVSS v3 Score Breakdown Red Hat NVD
CVSS v3 Base Score 5.5 5.5
Attack Vector Local Local
Attack Complexity Low Low
Privileges Required Low Low
User Interaction None None
Scope Unchanged Unchanged
Confidentiality Impact None None
Integrity Impact None None
Availability Impact High High

CVSS v3 Vector

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

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

Red Hat CVSS v3 Score Explanation

Attack Vector set to Local (AV:L) as the attack does not involve any network interaction. Privilege Required set to Low (PR:L) because an attacker needs to have at least some privileges on the system to mount a filesystem on a very long path. Availability set to High (A:H) considering that systemd and the whole system crashes.

Acknowledgements

Red Hat would like to thank Qualys Research Team 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.
  • "Affected" means that our Analysis Team has determined that this product is affected by this vulnerability and might release a fix to address this in the near future.

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 This content is not included.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 This content is not included.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 This content is not included.Red Hat Vulnerability Scanner Certification program.