Active Storage: Possible DoS vulnerability in Active Storage proxy mode via storage errors during streaming
- Exploited
- No known exploitation
- Fix
- Fixed in 8.1.4.1, 8.0.5.2
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 8.1.4.1, 8.0.5.2.
- 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? →
- 25/100 · provisional
- 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
Active Storage, the Rails component for handling uploaded files, has a flaw in its proxy download routes that a remote attacker with low-privilege login and no user action can reach to cause a denial of service. Repeated downloads that fail partway through, such as when a file is deleted while being served, can block server threads until the process restarts, potentially exhausting them.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
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. From 8.0 until 8.0.5.2 and 8.1.4.1, when Active Storage serves a file through its proxy controllers, ActiveStorage::Streaming#send_blob_stream handles an error from the storage service by calling head to send a 404 or 500 response. If the error occurs after the first chunk has been written, the response is already committed, and head replaces the response body while the server is still reading the original ActionController::Live buffer. That buffer is never closed, so the server thread handling the request blocks until the process restarts. Repeated failed downloads could exhaust the server's threads, possibly resulting in a DoS vulnerability. Applications are affected when they store files on a service that streams a download in several requests, such as Amazon S3, an S3-compatible service or Google Cloud Storage, and draw Active Storage's default routes. The proxy routes are drawn whether or not proxy mode is the default for the application. A file deleted while it is being served, or any other storage error partway through a download, triggers the condition. This issue is fixed in versions 8.1.4.1 and 8.0.5.2.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure3/25Reachable over the network · Unknown: No advisory context yet
- Reach17/20Affects Ruby on Rails (a widely deployed server, runtime, framework or database)
- Severity5.3/10CVSS 5.3
- No patch0/5No signal
What would change the score
- Would score about 80 if added to CISA KEV
- Would score about 75 if CISA's SSVC rates exploitation active
- Would score about 44 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 8.1.4.1, 8.0.5.2.
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-2026-126071 (Active Storage: Possible DoS vulnerability in Active Storage proxy mode via storage errors during streaming), 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-2026-126071 (entry last updated 2026-11-10): Affected: - rails rails: from 8.1, fixed in 8.1.4.1; from 8.0, fixed in 8.0.5.2 - RubyGems package activestorage: from 8.1.0.beta1, fixed in 8.1.4.1 - RubyGems package activestorage: from 8.0.0.beta1, fixed in 8.0.5.2 Fixed versions: 8.1.4.1, 8.0.5.2. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-126071 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126071 only. If you also check another CVE, look up its own KEV status; never assume it from this one. How to check: - Packages (RubyGems): find every lockfile in each project and run check_stack from the cve.now MCP server on each one. Compare the resolved versions, not the ranges a manifest declares, with the affected versions above. Include transitive dependencies. - 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-4v2w-w6g6-f8f8 - https://github.com/rails/rails/commit/3c67a693fb21870ecb1222e3da59d5c491a62009 - https://github.com/rails/rails/commit/655b4442de136a3701334607f634d698bf9d5b82 - 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-2026-126071 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-2026-126071.
Timeline
- CVE published
- First seen by cve.now
Affected versions
- rails rails
From 8.1 · fixed in 8.1.4.1; From 8.0 · fixed in 8.0.5.2
- activestorageRubyGems
From 8.1.0.beta1 · fixed in 8.1.4.1
- activestorageRubyGems
From 8.0.0.beta1 · 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.
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Questions about CVE-2026-126071
Is CVE-2026-126071 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
Which versions are affected by CVE-2026-126071?
rails: from 8.1 before 8.1.4.1; from 8.0 before 8.0.5.2. activestorage (RubyGems): from 8.1.0.beta1 before 8.1.4.1. activestorage (RubyGems): from 8.0.0.beta1 before 8.0.5.2.Source: cve.now feed data
How do I fix CVE-2026-126071?
Upgrade to a fixed version: 8.1.4.1, 8.0.5.2.Source: cve.now feed data