Active Storage: Possible arbitrary file write and read in Active Storage image analysis
Affects Rails Active Storage before 8.0.5.2 and 8.1 before 8.1.4.1 when ImageMagick (mini_magick) processes uploads from untrusted users under a policy that does not deny the coders involved. Fixed in 8.1.4.1 and 8.0.5.2.
Written by anthropic/claude-sonnet-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 8.1.4.1, 8.0.5.2
- Who is exposed
- Default setups
Do first: Check every install: default setups are affected.
- Last modified
- Whether it needs action now or is a reference record, by fixed rules, with why. Last checked is when cve.now last re-read it.What do these mean? →
- Reference
- Last checked
- A 0-100 score for how much a CVE matters across the industry: exploitation, exposure, how widely the software is used, severity and whether a fix exists.What do these mean? →
- 49/100 · provisional
- How many real-world setups can hit the bug, from the vendor's advisory and CISA data. It does not know your setup.What do these mean? →
- Default setups
- Whether working attack code is public (Exploit-DB, Metasploit, Nuclei or GitHub). Public code makes attacks easier.What do these mean? →
- None on Exploit-DB, Metasploit or GitHub
Summary
Rails applications that use Active Storage with ImageMagick to process uploaded images can let an unauthenticated attacker write arbitrary files on the server, and with Disk storage read files the app can access, such as secret keys and credentials, which may lead to remote code execution or lateral movement. The attacker reaches it remotely, without logging in, by uploading a crafted file to an app that accepts uploads from untrusted users.
Read the original description
Active Storage makes it simple to upload and reference files in cloud services and attach those files to Active Record objects. Prior to 8.1.4.1 and 8.0.5.2, a Rails application that processes attachments with ImageMagick may allow an unauthenticated attacker to write arbitrary files on the server and, when attachments are stored with the Disk service, to read arbitrary files readable by the application process. Those files typically include secret_key_base and credentials for external systems, which may in turn allow escalation to remote code execution or lateral movement to those systems. ImageMagick selects a coder from the content of the file it is given, and some coders act on files named inside the image rather than on the image itself. Active Storage constrained none of ImageMagick's coders, and the ImageMagick analyzer runs when a file is attached, so an attacker who can upload a crafted file may be able to invoke one. Attaching the upload is sufficient; no variant, preview, or analyze call is required. One specific attack chain has been reported, but other attack chains may exist. An application is affected when it uses ImageMagick for Active Storage image processing through config.active_storage.variant_processor = :mini_magick, runs ImageMagick under a security policy that does not already deny the involved coders, and allows uploads from untrusted users. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.
Who should check
Rails teams using Active Storage with mini_magick/ImageMagick (e.g. Debian/Ubuntu policies) that accept uploads from untrusted users, on activestorage before 8.0.5.2 or 8.1.4.1.
Read the source excerpt
“A Rails application that processes attachments with ImageMagick may allow an unauthenticated attacker to write arbitrary files on the server”
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure22/25Default setups, reachable over the network without a login
- Reach17/20Affects Ruby on Rails (a widely deployed server, runtime, framework or database)
- Severity9.8/10CVSS 9.8
- No patch0/5No signal
What would change the score
- Would score about 89 if added to CISA KEV
- Would score about 84 if CISA's SSVC rates exploitation active
What to do
Check every install: default setups are affected.
Upgrade to a fixed version: 8.1.4.1, 8.0.5.2.
Workaround: Copy the shipped policy rules into ImageMagick's system policy (e.g. /etc/ImageMagick-7/policy.xml); at minimum deny the MSL coder, the Ghostscript coders, and the gs delegate.
Check your systems with an agent
Paste this into a coding or ops agent. It checks your systems read-only and reports a table per asset.
Check whether my systems are affected by CVE-2026-126082 (Active Storage: Possible arbitrary file write and read in Active Storage image analysis), using the cve.now data below. Rules: work read-only. Do not run exploit code, proof-of-concept scripts or scanners that send attack payloads, and do not change any configuration, package, image or deployment. Report findings only. What cve.now has for CVE-2026-126082 (entry last updated 2026-11-10): Affected: - rails rails: from 8.1, fixed in 8.1.4.1; fixed in 8.0.5.2 Fixed versions: 8.1.4.1, 8.0.5.2. Conditions (all must be true for the bug to be hit): - Application uses ImageMagick for Active Storage image processing via the mini_magick variant processor (default for load_defaults 6.1 or earlier) (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) - ImageMagick runs under a security policy that does not already deny the involved coders (Debian and Ubuntu packaged policies do not) (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) - Application accepts file uploads from untrusted users (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) - Reading arbitrary files additionally requires attachments stored with the Disk service (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) - Affected activestorage versions: before 8.0.5.2, and 8.1 before 8.1.4.1 (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) Setup: the bug is reachable in a default setup; no special feature or setting is needed. Attacker needs: network access, no login, no user action. Workaround: Copy the shipped policy rules into ImageMagick's system policy (e.g. /etc/ImageMagick-7/policy.xml); at minimum deny the MSL coder, the Ghostscript coders, and the gs delegate. (source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9) CISA KEV: CVE-2026-126082 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126082 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Installed software: check what is actually running, not what a repo declares. Read the version from each host, container image and Kubernetes node (the binary's version output, the OS package database, image layers), and check whether the conditions above hold there. Distribution packages may carry a backported fix under an older version number; confirm against the distribution's own advisory. Verify against the linked advisories before concluding, and cite the date you read each one: - https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9 - https://github.com/rails/rails/commit/468aa9a93fc98f5476b6821770f4ccfcb7f7d328 - https://github.com/rails/rails/commit/ea8c40121ce53a3d0255cd4eb6d13bfe3bc01776 - https://github.com/rails/rails/releases/tag/v8.0.5.2 - https://github.com/rails/rails/releases/tag/v8.1.4.1 Do not conclude an asset is unaffected unless you checked it and the evidence covers both its version and the conditions above. If you could not check something, mark it unknown and say what is missing. Report a table with one row per asset and these columns: Asset | Version or build | Status (affected, fixed, not applicable, unknown) | Compensating controls | Exposure (internet-facing, internal, none) | Evidence | Next action. Entry: https://cve.now/CVE-2026-126082 For follow-up questions, use the cve.now MCP server at https://mcp.cve.now/mcp (no authentication), for example get_vulnerability with id CVE-2026-126082.
Timeline
- CVE published
- First seen by cve.now
- Posted on X by cve.now
Affected versions
- rails rails
From 8.1 · fixed in 8.1.4.1; fixed in 8.0.5.2
Evidence 7
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 4
- Repository
- Repository
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126082
Is CVE-2026-126082 being exploited?
It is not in CISA's Known Exploited Vulnerabilities catalog, and CISA's SSVC assessment does not mark exploitation as active. That does not mean it has not been attacked: vendors and researchers can report attacks before CISA lists them. No public exploit code is tracked.Source: cve.now feed data
What does this mean?
Active Storage's image analysis can be abused through a crafted upload to write arbitrary files on the server. With Disk storage, it can also read arbitrary files the app process can access, such as secret_key_base or credentials. The advisory says this may lead to remote code execution or lateral movement.Source: github.com
Which versions are affected by CVE-2026-126082?
rails: from 8.1 before 8.1.4.1; before 8.0.5.2.Source: cve.now feed data
Am I affected, and how do I check?
Affected activestorage versions are before 8.0.5.2, and 8.1 before 8.1.4.1. The setup also needs ImageMagick used for image processing (config.active_storage.variant_processor = :mini_magick, the default for load_defaults 6.1 or earlier), a security policy that does not deny the coders involved (Debian and Ubuntu packaged policies do not), and uploads from untrusted users. Reading files additionally needs the Disk service. Check the Rails version in Gemfile.lock, the variant_processor setting, and the ImageMagick policy file.Source: github.com
How do I fix CVE-2026-126082?
Upgrade to Rails 8.1.4.1 or 8.0.5.2. As a workaround, copy the shipped policy rules into ImageMagick's system policy (e.g. /etc/ImageMagick-7/policy.xml); at minimum deny the MSL coder, the Ghostscript coders, and the gs delegate.Source: github.com