CVE-2020-8165 — activesupport
CRITICALCVE-2020-8165 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in activesupport. 5 public exploit references exist, so weaponization risk is real. A fix is available for activesupport — see the affected versions and patch details below.
ActiveSupport potentially unintended unmarshalling of user-provided objects in MemCacheStore and RedisCacheStore
EPSS Exploitation Probability
EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.
How urgent is this, really
CVE-2020-8165 plotted by exploitation likelihood (EPSS) against impact (CVSS). The shaded corner — EPSS 50%+ and CVSS 7.0+ — is where this CVE doesn't sit, though severity or exploitability alone can still warrant action.
Where this sits among everything scored
Of 377,636 CVEs with a current EPSS score, this one falls in the 10–50% band (highlighted). Real counts from FIRST.org, not a sample — log-scaled since the landscape is heavily right-skewed.
Real-World Exposure
activesupport💎activesupportReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects RubyGems packages — download data is not available via public APIs for these ecosystems.
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.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 💎RubyGems | activesupport | ≥ 5.0.0&&< 5.2.4.3 | 5.2.4.3bundle update activesupport --conservative |
| 💎RubyGems | activesupport | ≥ 6.0.0&&< 6.0.3.1 | 6.0.3.1bundle update activesupport --conservative |
Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for activesupport, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update activesupport to 5.2.4.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2020-8165 is resolved across your whole dependency graph.
Workarounds
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2020-8165 can be triaged on real exposure rather than presence alone.
Tailored to CVE-2020-8165. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.
Fixing This On Your OS
If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.
This issue affects the version of rubygem-activesupport as shipped with Red Hat Gluster Storage 3. However, the 'raw' option is not used by the product when storing untrusted user input and hence this issue has been rated as having a security impact of Low. Red Hat Satellite ship affected RubyGem ActiveSupport and use…
| Product | Fixed in | Advisory |
|---|---|---|
| Red Hat Satellite 6.9 for RHEL 7 | ansible-collection-redhat-satellite-0:2.0.1-1.el7sat | RHSA-2021:1313 |
Frequently Asked Questions
Is CVE-2020-8165 in your dependencies?
O3 Security finds CVE-2020-8165 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.