Action Pack: Possible IP spoofing in Action Dispatch RemoteIp
Affects Rails 8.1.0 through 8.1.4 with Rack 3 behind a proxy that does not strip client Forwarded headers, where request.remote_ip drives access control, rate limiting, or auditing. Fixed in 8.1.4.1.
Written by anthropic/claude-haiku-5.5 from the sources below. Verify against them.
- Exploited
- No known exploitation
- Fix
- Fixed in 8.1.4.1
- Who is exposed
- Not reported
Do first: Upgrade to a fixed version: 8.1.4.1.
- 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? →
- 41/100 · 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? →
- Unclear
- 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
Action Pack is a framework for handling and responding to web requests. From 8.1 until 8.1.4.1, Since Rails 8.1.0, ActionDispatch::RemoteIp derives request.remote_ip from Rack::Request#forwarded_for, which under Rack 3 reads the RFC 7239 Forwarded header in preference to X-Forwarded-For. When a reverse proxy appends the client address to X-Forwarded-For but passes a client-supplied Forwarded header through unchanged, request.remote_ip returns an address chosen by the client, and the IP spoofing check does not raise, because it compares only Client-Ip with the forwarded addresses. An unauthenticated attacker could therefore spoof request.remote_ip, possibly bypassing IP-based access controls and rate limits keyed on the client address (including the default by: of rate_limit), and falsifying the client address in logs. An application is affected if it meets all of these requirements: Runs Rails 8.1.0 through 8.1.4 with Rack 3. Under Rack 2.2, forwarded_for reads only X-Forwarded-For. Is served behind a proxy that does not remove or overwrite a client-supplied Forwarded header. Relies on request.remote_ip for access control, rate limiting, or auditing. The fix detects a spoofed Forwarded header only when the proxy also sets X-Forwarded-For. An application whose proxy passes a client-supplied Forwarded header through and sets no X-Forwarded-For remains exposed after upgrading, and should configure the proxy to remove or overwrite Forwarded, or apply the workaround below. This issue is fixed in version 8.1.4.1.
Who should check
Teams running Rails 8.1.0 to 8.1.4 with Rack 3 behind a reverse proxy that passes Forwarded through, especially apps keying access control or rate limits on request.remote_ip
Not fixed by: Upgrading alone does not fix apps whose proxy sets no X-Forwarded-For.
cve.now Index
- Exploitation?/40Unknown. No CISA SSVC exploitation rating yet
- Exposure17/25No login or user action needed, reachable over the network without a login · Unknown: Advisories don't say whether default setups are affected
- Reach17/20Affects Ruby on Rails (a widely deployed server, runtime, framework or database)
- Severity7.4/10CVSS 7.4
- No patch0/5No signal
What would change the score
- Would score about 86 if added to CISA KEV
- Would score about 81 if CISA's SSVC rates exploitation active
- Would score about 46 if advisories confirm default setups are exposed
What to do
Upgrade to a fixed version: 8.1.4.1.
Workaround: When proxies set X-Forwarded-For, set Rack::Request.forwarded_priority = [:x_forwarded] in an initializer.
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-2026-126083 (Action Pack: Possible IP spoofing in Action Dispatch RemoteIp), 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-2026-126083 (entry last updated 2026-11-10): Affected: - rails rails: from 8.1, fixed in 8.1.4.1 - RubyGems package actionpack: from 8.1.0.beta1, fixed in 8.1.4.1 Fixed versions: 8.1.4.1. Conditions (all must be true for the bug to be hit): - Runs Rails 8.1.0 through 8.1.4 with Rack 3. (source: https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p) - Served behind a proxy that does not remove or overwrite a client-supplied Forwarded header. (source: https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p) - The application relies on request.remote_ip for access control, rate limiting, or auditing. (source: https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p) Setup: unknown whether the bug needs a non-default feature or setting. Check the advisory. Attacker needs: network access, no login, no user action. Workaround: When proxies set X-Forwarded-For, set Rack::Request.forwarded_priority = [:x_forwarded] in an initializer. (source: https://github.com/rails/rails/security/advisories/GHSA-2gff-2mmg-m73p) CISA KEV: CVE-2026-126083 is not listed as of cve.now's last read. This KEV status is for CVE-2026-126083 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-2gff-2mmg-m73p - https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227 - 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-2026-126083 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-2026-126083.
Timeline
- CVE published
- First seen by cve.now1 day
- Posted on X by cve.now
Affected versions
- rails rails
From 8.1 · fixed in 8.1.4.1
- actionpackRubyGems
From 8.1.0.beta1 · fixed in 8.1.4.1
Evidence 5
Vendor advisory · 1
Establishes: Affected and fixed versions.
- Advisory
CVE record · 2
Establishes: The identifier and description.
- Record
- Record
Other links · 2
- Repository
- Repository
Corrections
None so far.
Something wrong on this page? Report an error. Every fix is listed here.
Questions about CVE-2026-126083
Is CVE-2026-126083 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?
Action Dispatch's RemoteIp component can report a client IP address taken from a request header that the client supplied, so request.remote_ip may return an address other than the real one. Applications that make decisions based on that IP can be misled by it.Source: github.com
Which versions are affected by CVE-2026-126083?
rails: from 8.1 before 8.1.4.1. actionpack (RubyGems): from 8.1.0.beta1 before 8.1.4.1.Source: cve.now feed data
Am I affected, and how do I check?
Rails 8.1.0 through 8.1.4 (actionpack from 8.1.0.beta1 through 8.1.4) with Rack 3 are in scope, but only when the app is served behind a proxy that does not remove or overwrite a client-supplied Forwarded header and the app relies on request.remote_ip for access control, rate limiting, or auditing. To check, run bin/rails -v or look up actionpack and rack in Gemfile.lock, and review the proxy's header handling and the app's use of request.remote_ip.Source: github.com
How do I fix CVE-2026-126083?
Upgrade actionpack to 8.1.4.1 or later. If you cannot upgrade yet and your proxy sets X-Forwarded-For, the advisory's workaround is to set Rack::Request.forwarded_priority = [:x_forwarded] in an initializer.Source: github.com