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VulnerabilityPublished

CVE-2026-126075: rails · Cross-site Scripting

Affects railsSource CVE Database V5

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Not known to be exploited · CVSS 4.7 Medium : upgrade to 8.1.4.1 when convenient.

Data as of 10 Nov 2026, 21:17 UTC

CVSS 3.1 base score
4.7Medium
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 3.14.7
Patch
Available – fixed in 8.1.4.1
CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N

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.

Affected software

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

AI-suggested

Upgrade affected Rails applications to version 8.1.4.1 or later, where this issue is fixed. If upgrading immediately is not possible, avoid using MessagePack serializers for cookies, cache, or message verification/encryption with mutated SafeBuffer objects containing untrusted input. Review application code to prevent storing mutated SafeBuffer instances with untrusted data. Patch status is confirmed fixed in 8.1.4.1.

Description

A cross-site scripting (XSS) vulnerability exists in Rails versions 8.1 through 8.1.4 prior to 8.1.4.1 in the ActiveSupport::MessagePack serializer. This flaw occurs because mutated SafeBuffer objects containing untrusted input can be restored as html_safe, bypassing ERB auto-escaping and potentially enabling XSS when rendered. The issue affects applications using MessagePack serializers for cookies, cache, or message verification/encryption that store such mutated SafeBuffer instances. Rails 8.0 and earlier are not affected. The vulnerability is fixed in Rails 8.1.4.1.

References

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