CVE-2026-33658

Rails Active Storage has a possible DoS vulnerability in proxy mode via multi-range requests

Releases

The fixed releases are available at the normal locations.

Credit

This issue was responsibly reported by Hackerone researcher thwin_htet.

Active Storage's proxy controller does not limit the number of byte ranges in an HTTP Range header. A request with thousands of small ranges causes disproportionate CPU usage compared to a normal request for the same file, possibly resulting in a DoS vulnerability.

The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap. Typical impact: resource exhaustion leading to denial of service.

CVE-2026-33658 has a CVSS score of 6.5 (Low). The vector is network-reachable, low 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 (8.1.2.1, 8.0.4.1, 7.2.3.1); upgrading removes the vulnerable code path.

Kodem intelligence

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1. What is CVE-2026-33658? CVE-2026-33658 is a low-severity allocation of resources without limits or throttling vulnerability in activestorage (rubygems), affecting versions >= 8.1.0, < 8.1.2.1. It is fixed in 8.1.2.1, 8.0.4.1, 7.2.3.1. The application allocates resources such as memory, threads, or file descriptors based on untrusted input without enforcing a cap.
2. How severe is CVE-2026-33658? CVE-2026-33658 has a CVSS score of 6.5 (Low). 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.
3. Which versions of activestorage are affected by CVE-2026-33658? activestorage (rubygems) versions >= 8.1.0, < 8.1.2.1 is affected.
4. Is there a fix for CVE-2026-33658? Yes. CVE-2026-33658 is fixed in 8.1.2.1, 8.0.4.1, 7.2.3.1. Upgrade to this version or later.
5. Is CVE-2026-33658 exploitable, and should I be worried? Whether CVE-2026-33658 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
6. What actually determines whether CVE-2026-33658 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.
7. How do I fix CVE-2026-33658?
   • Upgrade activestorage to 8.1.2.1 or later
   • Upgrade activestorage to 8.0.4.1 or later
   • Upgrade activestorage to 7.2.3.1 or later

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