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CRITICAL severity

CVE-2018-16395 — openssl

CRITICAL

CVE-2018-16395 is a critical-severity (CVSS 9.8) vulnerability in openssl. EPSS puts its 30-day exploitation probability at 10.7% (96th percentile). A fix is available for openssl — see the affected versions and patch details below.

Ruby Openssl Allows Incorrect Value Comparison

Also known asGHSA-mmrq-6999-72v8
Published
Nov 16, 2018
Updated
Jul 8, 2026
Affected
2 pkgs
Patched
2 / 2
Exploits
None indexed
Exploitation data as of Sep 20, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗
10.7%probability of exploitation in next 30 days
Moderate Risk0.00%
Lower risk than most CVEs96th percentile — riskier than 96% of all scored CVEsHighest risk

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-2018-16395 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 377,333 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

2 pkgs affected
💎openssl💎openssl

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

An issue was discovered in the OpenSSL library in Ruby before 2.3.8, 2.4.x before 2.4.5, 2.5.x before 2.5.2, and 2.6.x before 2.6.0-preview3. When two OpenSSL::X509::Name objects are compared using ==, depending on the ordering, non-equal objects may return true. When the first argument is one character longer than the second, or the second argument contains a character that is one less than a character in the same position of the first argument, the result of == will be true. This could be leveraged to create an illegitimate certificate that may be accepted as legitimate and then used in signing or encryption operations.

Affected Packages

2 total 2 fixed
EcosystemPackageVulnerable rangeFix
💎RubyGemsopensslall versions2.0.9bundle update openssl --conservative
💎RubyGemsopenssl≥ 2.1.0&&< 2.1.22.1.2bundle update openssl --conservative

Detection & mitigation playbook

Open-source dependency

  1. Detect

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

  2. Fix

    Update openssl to 2.0.9 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2018-16395 is resolved across your whole dependency graph.

  3. 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.

  4. How O3 protects you

    O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2018-16395 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2018-16395. 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.

Red HatImportant

Subscription Asset Manager is now in a reduced support phase receiving only Critical impact security fixes. This issue has been rated as having a security impact of Important, and is not currently planned to be addressed in future updates. Red Hat Virtualization includes a vulnerable version of ruby, however the…

ProductFixed inAdvisory
Red Hat Enterprise Linux 7ruby-0:2.0.0.648-34.el7_6RHSA-2018:3738
Red Hat Enterprise Linux 7.4 Extended Update Supportruby-0:2.0.0.648-34.el7_4RHSA-2019:1948
Red Hat Enterprise Linux 7.5 Extended Update Supportruby-0:2.0.0.648-34.el7_5RHSA-2019:2565
Red Hat Software Collections for Red Hat Enterprise Linux 6rh-ruby23-ruby-0:2.3.8-69.el6RHSA-2018:3729
Red Hat Software Collections for Red Hat Enterprise Linux 6rh-ruby24-ruby-0:2.4.5-91.el6RHSA-2018:3730
Red Hat Software Collections for Red Hat Enterprise Linux 7rh-ruby25-ruby-0:2.5.3-6.el7RHSA-2018:3731
UbuntuCRITICAL
USN-3808-1Ubuntu

Frequently Asked Questions

An issue was discovered in the OpenSSL library in Ruby before 2.3.8, 2.4.x before 2.4.5, 2.5.x before 2.5.2, and 2.6.x before 2.6.0-preview3. When two OpenSSL::X509::Name objects are compared using ==, depending on the ordering, non-equal objects may return true. When the first argument is one character longer than the second, or the second argument contains a character that is one less than a character in the same position of the first argument, the result of == will be true. This could be leveraged to create an illegitimate certificate that may be accepted as legitimate and then used in sign
O3 Security · Impact-Aware SCA

Is CVE-2018-16395 in your dependencies?

O3 Security finds CVE-2018-16395 across RubyGems dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works
CVE-2018-16395: openssl (Critical 9.8) | O3 Security