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Bypass of fix for CVE-2020-26231, Twig sandbox escape

Moderate severity GitHub Reviewed Published May 2, 2021 in octobercms/october • Updated Feb 1, 2023

Package

composer october/cms (Composer)

Affected versions

= 1.0.471
= 1.1.1

Patched versions

1.0.472
1.1.2

Description

Impact

A bypass of CVE-2020-26231 (fixed in 1.0.470/471 and 1.1.1) was discovered that has the same impact as CVE-2020-26231 & CVE-2020-15247:

An authenticated backend user with the cms.manage_pages, cms.manage_layouts, or cms.manage_partials permissions who would normally not be permitted to provide PHP code to be executed by the CMS due to cms.enableSafeMode being enabled is able to write specific Twig code to escape the Twig sandbox and execute arbitrary PHP.

This is not a problem for anyone that trusts their users with those permissions to normally write & manage PHP within the CMS by not having cms.enableSafeMode enabled, but would be a problem for anyone relying on cms.enableSafeMode to ensure that users with those permissions in production do not have access to write & execute arbitrary PHP.

Patches

Issue has been patched in Build 472 (v1.0.472) and v1.1.2.

Workarounds

Apply octobercms/october@f63519f to your installation manually if unable to upgrade to Build 472 or v1.1.2.

References

Reported by ka1n4t

For more information

If you have any questions or comments about this advisory:

Threat assessment:

Screen Shot 2020-10-10 at 1 21 13 PM

### References - https://github.com/octobercms/october/security/advisories/GHSA-fcr8-6q7r-m4wg - https://nvd.nist.gov/vuln/detail/CVE-2021-21264
@daftspunk daftspunk published to octobercms/october May 2, 2021
Reviewed May 3, 2021
Published by the National Vulnerability Database May 3, 2021
Published to the GitHub Advisory Database May 4, 2021
Last updated Feb 1, 2023

Severity

Moderate

CVSS overall score

This score calculates overall vulnerability severity from 0 to 10 and is based on the Common Vulnerability Scoring System (CVSS).
/ 10

CVSS v3 base metrics

Attack vector
Local
Attack complexity
Low
Privileges required
High
User interaction
Required
Scope
Changed
Confidentiality
Low
Integrity
Low
Availability
Low

CVSS v3 base metrics

Attack vector: More severe the more the remote (logically and physically) an attacker can be in order to exploit the vulnerability.
Attack complexity: More severe for the least complex attacks.
Privileges required: More severe if no privileges are required.
User interaction: More severe when no user interaction is required.
Scope: More severe when a scope change occurs, e.g. one vulnerable component impacts resources in components beyond its security scope.
Confidentiality: More severe when loss of data confidentiality is highest, measuring the level of data access available to an unauthorized user.
Integrity: More severe when loss of data integrity is the highest, measuring the consequence of data modification possible by an unauthorized user.
Availability: More severe when the loss of impacted component availability is highest.
CVSS:3.1/AV:L/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L

EPSS score

0.044%
(13th percentile)

Weaknesses

CVE ID

CVE-2021-21264

GHSA ID

GHSA-fcr8-6q7r-m4wg

Source code

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