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ActiveSupport potentially unintended unmarshalling of user-provided objects in MemCacheStore and RedisCacheStore

Critical severity GitHub Reviewed Published May 26, 2020 to the GitHub Advisory Database • Updated Aug 17, 2023

Package

bundler activesupport (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

In ActiveSupport, there is potentially unexpected behaviour in the MemCacheStore and RedisCacheStore where, when
untrusted user input is written to the cache store using the raw: true parameter, re-reading the result
from the cache can evaluate the user input as a Marshalled object instead of plain text. Vulnerable code looks like:

data = cache.fetch("demo", raw: true) { untrusted_string }

Versions Affected: rails < 5.2.5, rails < 6.0.4
Not affected: Applications not using MemCacheStore or RedisCacheStore. Applications that do not use the raw option when storing untrusted user input.
Fixed Versions: rails >= 5.2.4.3, rails >= 6.0.3.1

Impact

Unmarshalling of untrusted user input can have impact up to and including RCE. At a minimum,
this vulnerability allows an attacker to inject untrusted Ruby objects into a web application.
In addition to upgrading to the latest versions of Rails, developers should ensure that whenever
they are calling Rails.cache.fetch they are using consistent values of the raw parameter for both
reading and writing, especially in the case of the RedisCacheStore which does not, prior to these changes,
detect if data was serialized using the raw option upon deserialization.

Workarounds

It is recommended that application developers apply the suggested patch or upgrade to the latest release as
soon as possible. If this is not possible, we recommend ensuring that all user-provided strings cached using
the raw argument should be double-checked to ensure that they conform to the expected format.

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 Aug 17, 2023

Severity

Critical

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
High
Integrity
High
Availability
High

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:H/I:H/A:H

EPSS score

66.305%
(98th percentile)

Weaknesses

CVE ID

CVE-2020-8165

GHSA ID

GHSA-2p68-f74v-9wc6

Source code

No known source code
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