CVE-2026-126071 (CVSS 5.3)

Description

Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. From 8.0 until 8.0.5.2 and 8.1.4.1, when Active Storage serves a file through its proxy controllers, ActiveStorage::Streaming#send_blob_stream handles an error from the storage service by calling head to send a 404 or 500 response. If the error occurs after the first chunk has been written, the response is already committed, and head replaces the response body while the server is still reading the original ActionController::Live buffer. That buffer is never closed, so the server thread handling the request blocks until the process restarts. Repeated failed downloads could exhaust the server's threads, possibly resulting in a DoS vulnerability. Applications are affected when they store files on a service that streams a download in several requests, such as Amazon S3, an S3-compatible service or Google Cloud Storage, and draw Active Storage's default routes. The proxy routes are drawn whether or not proxy mode is the default for the application. A file deleted while it is being served, or any other storage error partway through a download, triggers the condition. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Is your site exposed to CVE-2026-126071?

Run a free security scan — no signup, results in seconds.

CVSS v3.1 Score

5.3

MEDIUM

CVSS:3.1/AV:N/AC:H/PR:L/UI:N/S:U/C:N/I:N/A:H

EPSS — Exploit Prediction

0.0044

Probability of exploitation

0.39%

Percentile rank

EPSS estimates the probability that this vulnerability will be exploited in the wild within the next 30 days. A higher score means more likely to be exploited.

Weakness Type (CWE)

CWE-772 CWE-772

References

Other References

https://github.com/rails/rails/commit/3c67a693fb21870ecb1222e3da59d5c491a62009 https://github.com/rails/rails/commit/655b4442de136a3701334607f634d698bf9d5b82 https://github.com/rails/rails/releases/tag/v8.0.5.2 https://github.com/rails/rails/releases/tag/v8.1.4.1 https://github.com/rails/rails/security/advisories/GHSA-4v2w-w6g6-f8f8

Frequently Asked Questions

What is CVE-2026-126071? +

Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. From 8.0 until 8.0.5.2 and 8.1.4.1, when Active Storage serves a file through its proxy controllers, ActiveStorage::Streaming#send_blob_stream handles an error from the storage service by calling head to send a 404 or 500 response. If the error occurs after the first chunk has been written, the response is already committed, and head replaces the response body while the server is still reading the original ActionController::Live buffer. That buffer is never closed, so the server thread handling the request blocks until the process restarts. Repeated failed downloads could exhaust the server's threads, possibly resulting in a DoS vulnerability. Applications are affected when they store files on a service that streams a download in several requests, such as Amazon S3, an S3-compatible service or Google Cloud Storage, and draw Active Storage's default routes. The proxy routes are drawn whether or not proxy mode is the default for the application. A file deleted while it is being served, or any other storage error partway through a download, triggers the condition. This issue is fixed in versions 8.1.4.1 and 8.0.5.2. It has a CVSS v3.1 base score of 5.3 (MEDIUM).

How severe is CVE-2026-126071? +

CVE-2026-126071 has a CVSS v3.1 score of 5.3 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance. The EPSS score is 0.0044, placing it in the 0th percentile for exploitation probability.

How do I check if I'm vulnerable to CVE-2026-126071? +

You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

Related Vulnerabilities

CVE-2026-95108

One logical thread of a user-mode ThreadX module costs the Module Manager's shared object pool two allocations, not one. The …

CVE-2026-93926

Missing release of memory after effective lifetime, Missing release of resource after effective lifetime vulnerability in Apache Thrift THeaderTransport. This …

CVE-2025-65947

thread-amount is a tool that gets the amount of threads in the current process. Prior to version 0.2.2, there are …

CVE-2026-35227

An unauthenticated remote attacker may exhaust all available TCP connections in the CODESYS Modbus TCP Server stack if a race …

CVE-2026-118262

Echo is a Go web framework. From 4.15.0 until 4.16.1 and 5.4.1, Echo's Proxy middleware can retain a handler, copy …

CVE-2026-45287

OpenTelemetry-Go is the Go implementation of OpenTelemetry. Prior to version 0.0.17, `go.opentelemetry.io/otel/schema/v1.0` and `go.opentelemetry.io/otel/schema/v1.1` leaks one file descriptor on each …