How severe is CVE-2015-4020?

No CVSS score has been assigned to CVE-2015-4020 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2015-4020?

CVE-2015-4020 affects the following packages: rubygems-update (RubyGems), rubygems-update (RubyGems), rubygems-update (RubyGems). Ecosystems affected: RubyGems.

How do I fix CVE-2015-4020?

Update rubygems-update to 2.0.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2015-4020 is resolved across your whole dependency graph.

How do I detect CVE-2015-4020 in my RubyGems dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rubygems-update, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2015-4020 if there is no patch (or I can't update yet)?

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.

Is CVE-2015-4020 actively exploited in the wild?

No public exploit code has been indexed for CVE-2015-4020 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2015-4020?

CVE-2015-4020 has an EPSS (Exploit Prediction Scoring System) score of 3.5%, placing it in the 89th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2015-4020?

CVE-2015-4020 is classified as Improper Input Validation (CWE-20). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2015-4020 published, and has it been updated?

CVE-2015-4020 was published on May 17, 2022 and was last updated on December 2, 2024. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

CVE-2015-4020: rubygems-update

EPSS Exploitation Probability

via FIRST.org ↗

3.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs89th percentile — riskier than 89% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

3 pkgs affected

💎rubygems-update💎rubygems-update💎rubygems-update

Real-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

RubyGems 2.0.x before 2.0.17, 2.2.x before 2.2.5, and 2.3.x before 2.4.8 does not validate the hostname when fetching gems or making API requests, which allows remote attackers to redirect requests to arbitrary domains via a crafted DNS SRV record with a domain that is suffixed with the original domain name, aka a "DNS hijack attack."

NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-3900.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
💎RubyGems	`rubygems-update`	all versions	2.0.17`bundle update rubygems-update --conservative`
💎RubyGems	`rubygems-update`	≥ 2.1.0.rc.1&&< 2.2.5	2.2.5`bundle update rubygems-update --conservative`
💎RubyGems	`rubygems-update`	≥ 2.3.0&&< 2.4.8	2.4.8`bundle update rubygems-update --conservative`

Affected Products

2 products · 36 configurations

OS

solarisoracle

1 version

11.3

Application

rubygemsrubygems

30 versions

2.0.02.0.12.0.22.0.32.0.42.0.52.0.62.0.72.0.82.0.92.0.102.0.11

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for rubygems-update, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update rubygems-update to 2.0.17 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2015-4020 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.

Frequently Asked Questions

RubyGems 2.0.x before 2.0.17, 2.2.x before 2.2.5, and 2.3.x before 2.4.8 does not validate the hostname when fetching gems or making API requests, which allows remote attackers to redirect requests to arbitrary domains via a crafted DNS SRV record with a domain that is suffixed with the original domain name, aka a "DNS hijack attack." NOTE: this vulnerability exists because of an incomplete fix for CVE-2015-3900.

O3 Security · Impact-Aware SCA

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CVE-2015-4020 — rubygems-update