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Circumvention of file size limits in ActiveStorage

High severity GitHub Reviewed Published May 26, 2020 to the GitHub Advisory Database • Updated Jul 5, 2023

Package

bundler activestorage (RubyGems)

Affected versions

>= 5.0.0, <= 5.2.4.2
>= 6.0.0, <= 6.0.3

Patched versions

5.2.4.3
6.0.3.1

Description

There is a vulnerability in ActiveStorage's S3 adapter that allows the Content-Length of a direct file upload to be modified by an end user.

Versions Affected: rails < 5.2.4.2, rails < 6.0.3.1
Not affected: Applications that do not use the direct upload functionality of the ActiveStorage S3 adapter.
Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1

Impact

Utilizing this vulnerability, an attacker can control the Content-Length of an S3 direct upload URL without receiving a new signature from the server. This could be used to bypass controls in place on the server to limit upload size.

Workarounds

This is a low-severity security issue. As such, no workaround is necessarily until such time as the application can be upgraded.

References

Reviewed May 26, 2020
Published to the GitHub Advisory Database May 26, 2020
Published by the National Vulnerability Database Jun 19, 2020
Last updated Jul 5, 2023

Severity

High

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
Network
Attack complexity
Low
Privileges required
None
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

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:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:N

EPSS score

0.246%
(65th percentile)

CVE ID

CVE-2020-8162

GHSA ID

GHSA-m42x-37p3-fv5w

Source code

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