Summary
Regular expression denial of service vulnerability (ReDoS) in date
Date’s parsing methods including Date.parse are using Regexps internally, some of which are vulnerable against regular expression denial of service. Applications and libraries that apply such methods to untrusted input may be affected.
The fix limits the input length up to 128 bytes by default instead of changing the regexps. This is because Date gem uses many Regexps and it is possible that there are still undiscovered vulnerable Regexps. For compatibility, it is allowed to remove the limitation by explicitly passing limit keywords as nil like Date.parse(str, limit: nil), but note that it may take a long time to parse.
Please update the date gem to version 3.2.1, 3.1.2, 3.0.2, and 2.0.1, or later. You can use gem update date to update it. If you are using bundler, please add gem "date", ">= 3.2.1" to your Gemfile. If you import date from the standard library rather than as a gem you should update your Ruby install to 3.0.3, 2.7.5, 2.6.9 or later.
Users unable to upgrade may consider using Date.strptime instead with a predefined date format
Date.strptime('2001-02-20', '%Y-%m-%d')
Impact
A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use. Typical impact: denial of service when input is crafted to trigger backtracking.
CVE-2021-41817 has a CVSS score of 7.5 (High). The vector is network-reachable, no privileges required, and no user interaction. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (3.2.1, 3.1.2, 3.0.2, 2.0.1); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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date to 3.2.1 or later; date to 3.1.2 or later; date to 3.0.2 or later; date to 2.0.1 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2021-41817? CVE-2021-41817 is a high-severity inefficient regular expression (ReDoS) vulnerability in date (rubygems), affecting versions >= 3.2.0, < 3.2.1. It is fixed in 3.2.1, 3.1.2, 3.0.2, 2.0.1. A regular expression with worst-case exponential or polynomial matching time is applied to untrusted input, causing excessive CPU use.
- How severe is CVE-2021-41817? CVE-2021-41817 has a CVSS score of 7.5 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of date are affected by CVE-2021-41817? date (rubygems) versions >= 3.2.0, < 3.2.1 is affected.
- Is there a fix for CVE-2021-41817? Yes. CVE-2021-41817 is fixed in 3.2.1, 3.1.2, 3.0.2, 2.0.1. Upgrade to this version or later.
- Is CVE-2021-41817 exploitable, and should I be worried? Whether CVE-2021-41817 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2021-41817 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2021-41817?
- Upgrade
dateto 3.2.1 or later - Upgrade
dateto 3.1.2 or later - Upgrade
dateto 3.0.2 or later - Upgrade
dateto 2.0.1 or later
- Upgrade