VulnerabilityPublished 10 Nov 2026

CVE-2026-126083: Action Pack · Possible IP spoofing in Action Dispatch RemoteIp

Affects actionpackSource GCVE Database

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Authoritative record:CVE-2026-126083· High 7.4

Not known to be exploited · CVSS 7.4 High : upgrade to 8.1.4.1 soon.

Data as of 10 Nov 2026, 22:34 UTC

CVSS 3.0 base score

7.4High

How severe the flaw is on the 0–10 CVSS scale.

Thin evidence

One scorer or none

CVSS scores by source
CNA (GitHub_M)	CVSS 3.0	7.4

Patch: Available – fixed in 8.1.4.1

CVSS:3.0/AV:N/AC:H/PR:N/UI:N/S:U/C:H/I:H/A:N

Attack Vector: Network
Attack Complexity: High
Privileges Required: None
User Interaction: None
Scope: Unchanged
Confidentiality: High
Integrity: High
Availability: None

Bold values are the worst case: easiest to exploit or largest impact.

Attack Vector: Network: The vulnerable component is bound to the network stack and the set of possible attackers extends beyond the other options listed, up to and including the entire Internet. Such a vulnerability is often termed 'remotely exploitable' and can be thought of as an attack being exploitable at the protocol level one or more network hops away (e.g., across one or more routers).
Attack Complexity: High: A successful attack depends on conditions beyond the attacker's control. That is, a successful attack cannot be accomplished at will, but requires the attacker to invest in some measurable amount of effort in preparation or execution against the vulnerable component before a successful attack can be expected. For example, a successful attack may require an attacker to: gather knowledge about the environment in which the vulnerable target/component exists; prepare the target environment to improve exploit reliability; or inject themselves into the logical network path between the target and the resource requested by the victim in order to read and/or modify network communications (e.g., a man in the middle attack).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without any interaction from any user.
Scope: Unchanged: An exploited vulnerability can only affect resources managed by the same security authority. In this case, the vulnerable component and the impacted component are either the same, or both are managed by the same security authority.
Confidentiality: High: There is total loss of confidentiality, resulting in all resources within the impacted component being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact.
Integrity: High: There is a total loss of integrity, or a complete loss of protection. For example, the attacker is able to modify any/all files protected by the impacted component. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the impacted component.
Availability: None: There is no impact to availability within the impacted component.

Definitions: FIRST CVSS v3.1 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 10 Nov 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by Mirage: no evidence on record.
No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 10 Nov 2026.

Disclosed: The CVE record is public on cve.org. Its publication is t = 0.
Detectable: A public nuclei template can find exposed instances, for defenders and attackers alike.
Weaponized: A Metasploit exploit module or Exploit-DB entry exists (Metasploit scanner modules do not count), or CISA SSVC or the CVSS exploit maturity reports a public proof of concept.
Exploited in the wild: CISA KEV lists it, CISA SSVC rates exploitation active, or a source reports attacks.
Observed by OffSeq Mirage: OffSeq Mirage honeypot sensors recorded attack traffic for this CVE, or found exposed hosts without attack traffic.

Moments are spaced evenly, not to scale; a dashed line marks a gap of six months or more. Deltas count from t = 0. Sources that give only a date (CISA KEV, Exploit-DB, or a time of exactly 00:00Z) read “same day” rather than hours. Metasploit modules carry the flaw’s disclosure date, not their release date, and nuclei templates carry no date, so both appear above but not on the timeline.

What to do

Upgrade actionpack to 8.1.4.1.

Affected software

Product	Affected	Fixed in
RubyGemsactionpack	Affected >=8.1.0.beta1 <8.1.4.1	Fixed in 8.1.4.1

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

Description

### Impact 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. ### Details The 8.1.0 change ([2d084af8](https://github.com/rails/rails/commit/2d084af8444a7b6b868c7cbb256172007871e78d)) switched `ActionDispatch::RemoteIp` from reading `X-Forwarded-For` directly to Rack's `forwarded_for`, in order to reuse Rack's port handling. Rails continues to honor `Forwarded`, the standard header. In the fixed releases, when `config.action_dispatch.ip_spoofing_check` is enabled (the default), `ActionDispatch::RemoteIp` also compares the first untrusted client address in `Forwarded` with the first untrusted client address in `X-Forwarded-For`, as exact strings, and raises `ActionDispatch::RemoteIp::IpSpoofAttackError` when both headers are present and the addresses differ. Deployments whose proxies report the client address inconsistently between the two headers will receive this error after upgrading. See the `actionpack` CHANGELOG. ### Affected applications 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. ### Mitigation - Upgrade to a fixed version of `actionpack`. - Configure reverse proxies to remove or overwrite any client-supplied `Forwarded` header. ### Workarounds Applications whose proxies set `X-Forwarded-For` can make Rack ignore the `Forwarded` header, restoring the client address resolution of Rails 8.0, by setting `Rack::Request.forwarded_priority = [:x_forwarded]` in an initializer. This setting is available in Rack 3.0.0 and later, and it also causes Rack to ignore `Forwarded` when determining the request scheme, host, and port. ### Releases The fixed releases are available at the normal locations. Patches for those who cannot upgrade at once: - 8.1: https://github.com/rails/rails/commit/2a01a5ac521184419d9a92fa2c25e102e68cd227.patch ### Versions affected - actionpack >= 8.1, < 8.1.4.1 ### Credit This issue was responsibly reported by HackerOne researcher [luryus](https://hackerone.com/luryus).

CWE-348Use of Less Trusted Source (opens in a new tab)
Base weakness
The product has two different sources of the same data or information, but it uses the source that has less support for verification, is less trusted, or is less resistant to attack.
OWASP Cheat Sheets
XML Security (opens in a new tab)
REST Security (opens in a new tab)
JSON Web Token for Java (opens in a new tab)
REST Assessment (opens in a new tab)
Cross-Site Request Forgery Prevention (opens in a new tab)
OWASP ASVS 4.0.3
V13.3.2 (opens in a new tab)
V3.5.3 (opens in a new tab)
V13.2.6 (opens in a new tab)
Attack patterns
Cache Poisoning (opens in a new tab)
DNS Cache Poisoning (opens in a new tab)
User-Controlled Filename (opens in a new tab)
Manipulating Web Input to File System Calls (opens in a new tab)
AJAX Footprinting (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

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Exploitation evidence

What to do

Affected software

Description

WeaknessesCWE-348

Technical details

References

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