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VulnerabilityPublished

CVE-2026-126072: rails · Deadlock

Affects railsSource CVE Database V5

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Not known to be exploited · CVSS 5.9 Medium : upgrade to 8.1.4.1 or 8.0.5.2 when convenient.

Data as of 10 Nov 2026, 21:07 UTC

CVSS 3.1 base score
5.9Medium
How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none
CVSS scores by source
CNA (GitHub_M)CVSS 3.15.9
Patch
Available – fixed in 8.1.4.1, 8.0.5.2
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 10 Nov 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

What to do

Upgrade rails to 8.1.4.1 or 8.0.5.2.

Affected software

ProductAffectedFixed in
railsrailsAffected
  • >=8.1 <8.1.4.1
Fixed in
  • 8.1.4.1
railsrailsAffected
  • <8.0.5.2
Fixed in
  • 8.0.5.2

AI-suggested

Upgrade affected Rails versions to 8.1.4.1 or 8.0.5.2 where the issue is fixed. No other mitigation is indicated by the vendor advisory. Applying these official fixes will resolve the deadlock vulnerability and prevent denial of service through thread exhaustion.

Description

A deadlock vulnerability exists in the Action Pack framework of Rails prior to versions 8.1.4.1 and 8.0.5.2. The issue occurs in ActionController::Live::Buffer#close when it attempts to push an end-of-stream marker onto a bounded queue while holding a monitor lock. If the client stops reading and the queue is full, this push operation blocks, causing a deadlock with Buffer#abort, which waits for the same monitor. This can permanently hold web server threads, leading to denial of service through thread exhaustion. Applications using streaming responses with ActionController::Live, including send_stream and large file serving via Active Storage proxy mode, are affected. The vulnerability has a CVSS score of 5.9 and is fixed in versions 8.1.4.1 and 8.0.5.2.

References

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