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Fencer Intel
medium 5.9

CVE-2026-126072 json

Action Pack: Possible DoS vulnerability in Action Controller Live streaming

published 8d ago modified yesterday also EUVD-2026-123002 , GHSA-rwvh-fw6r-pwvp

Unreviewed: the maintainers' own advisory

Published by the maintainers on their GitHub repository rails/rails. GitHub has not reviewed it into the GitHub Advisory Database, so the affected packages and versions are the maintainers' word. Read the full advisory on GitHub.

cvss
5.9
version 3.1, CNA
cisa kev
Not listed
not in CISA's catalog
epss
0.4%
EPSS 0.4% chance of exploitation in 30 days, percentile 35%
public exploits
0
none known

Summary

Action Pack is a framework for handling and responding to web requests. Prior to 8.1.4.1 and 8.0.5.2, ActionController::Live::Buffer#close pushes its end-of-stream marker onto the response's bounded queue while it holds the buffer's monitor. When the client has stopped reading and the queue is full, the push blocks, and Buffer#abort, which runs when the client disconnects or a write times out, waits indefinitely for the same monitor. Each such response could permanently hold a web server thread and its ActionController::Live thread, possibly resulting in a DoS vulnerability through thread exhaustion. Applications that stream responses with ActionController::Live, including send_stream, are affected. Applications that serve large files through Active Storage proxy mode are exposed to unauthenticated clients. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.

Patch / fix

  • rubygems actionpack 8.0.5.2, 8.1.4.1

Is CVE-2026-126072 in your dependencies? Fencer shows which of your repositories are affected as soon as an advisory lands, and opens the fix as a pull request.

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Exploit prediction

0.41% chance of exploitation in the next 30 days, higher than 35% of all scored CVEs (FIRST EPSS, 2026-11-11).

CVSS scores

assigned by version score vector
CNA 3.1 5.9 CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Affected packages

ecosystem package affected fixed in
rubygems actionpack
>=8.1, <8.1.4.1
<8.0.5.2
8.1.4.1
8.0.5.2

Affected products

  • rails rails

Classification

Weakness
Technology feeds

References

Sources

Fencer Intel keeps one entry per vulnerability: the CVE id wins, then GHSA, and records that alias each other are merged, except that two CVEs always keep separate entries. The same data is available as JSON.

The maintainers of rails/rails published their own advisory on GitHub. Reviewed sources take precedence over it.