Summary
There is a denial of service vulnerability in the header parsing component of Rack. This vulnerability has been assigned the CVE identifier CVE-2023-27539.
Versions Affected: >= 2.0.0 Not affected: None. Fixed Versions: 2.2.6.4, 3.0.6.1
Workarounds
Setting Regexp.timeout in Ruby 3.2 is a possible workaround.
Impact
Carefully crafted input can cause header parsing in Rack to take an unexpected amount of time, possibly resulting in a denial of service attack vector. Any applications that parse headers using Rack (virtually all Rails applications) are impacted.
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.
Remediation advice
rack to 2.2.6.4 or later; rack to 3.0.6.1 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2023-27539? CVE-2023-27539 is a low-severity security vulnerability in rack (rubygems), affecting versions >= 2.0.0, < 2.2.6.4. It is fixed in 2.2.6.4, 3.0.6.1.
- Which versions of rack are affected by CVE-2023-27539? rack (rubygems) versions >= 2.0.0, < 2.2.6.4 is affected.
- Is there a fix for CVE-2023-27539? Yes. CVE-2023-27539 is fixed in 2.2.6.4, 3.0.6.1. Upgrade to this version or later.
- Is CVE-2023-27539 exploitable, and should I be worried? Whether CVE-2023-27539 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-2023-27539 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-2023-27539?
- Upgrade
rackto 2.2.6.4 or later - Upgrade
rackto 3.0.6.1 or later
- Upgrade