CVE-2026-66066VulnerabilityPublished 30 Jul 2026

Activestorage: Active Storage has possible arbitrary file read and remote code execution in Active Storage variant

Affects activestorageSource GCVE Database

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Public exploit available (Metasploit) · 26% EPSS · CVSS 9.5 Critical : upgrade to 7.2.3.2 as a priority.

Data as of 29 Oct 2026, 07:15 UTC

CVSS 4.0 base score

9.5Critical

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

EPSS: 26.5% chance of exploitation in 30 days – higher than 98% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch: Available – fixed in 7.2.3.2, 8.0.5.1, 8.1.3.1

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Attack Vector: Network
Attack Complexity: Low
Attack Requirements: Present
Privileges Required: None
User Interaction: None
Vulnerable system confidentiality: High
Vulnerable system integrity: High
Vulnerable system availability: High
Subsequent system confidentiality: High
Subsequent system integrity: High
Subsequent system availability: High

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

Attack Vector: Network: The vulnerable system is bound to the network stack and the set of possible attackers extends beyond the other options listed below, 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: Low: The attacker must take no measurable action to exploit the vulnerability. The attack requires no target-specific circumvention to exploit the vulnerability. An attacker can expect repeatable success against the vulnerable system.
Attack Requirements: Present: The successful attack depends on the presence of specific deployment and execution conditions of the vulnerable system that enable the attack. These include: a race condition must be won to successfully exploit the vulnerability (the successfulness of the attack is conditioned on execution conditions that are not under full control of the attacker, or the attack may need to be launched multiple times against a single target before being successful); the attacker must inject themselves into the logical network path between the target and the resource requested by the victim (e.g. vulnerabilities requiring an on-path attacker).
Privileges Required: None: The attacker is unauthorized prior to attack, and therefore does not require any access to settings or files of the vulnerable system to carry out an attack.
User Interaction: None: The vulnerable system can be exploited without interaction from any human user, other than the attacker.
Vulnerable system confidentiality: High: There is a total loss of confidentiality, resulting in all information within the Vulnerable System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Vulnerable system 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 vulnerable system. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the vulnerable system.
Vulnerable system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Vulnerable System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Vulnerable System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).
Subsequent system confidentiality: High: There is a total loss of confidentiality, resulting in all resources within the Subsequent System being divulged to the attacker. Alternatively, access to only some restricted information is obtained, but the disclosed information presents a direct, serious impact. For example, an attacker steals the administrator's password, or private encryption keys of a web server.
Subsequent system 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 Subsequent System. Alternatively, only some files can be modified, but malicious modification would present a direct, serious consequence to the Subsequent System.
Subsequent system availability: High: There is a total loss of availability, resulting in the attacker being able to fully deny access to resources in the Subsequent System; this loss is either sustained (while the attacker continues to deliver the attack) or persistent (the condition persists even after the attack has completed). Alternatively, the attacker has the ability to deny some availability, but the loss of availability presents a direct, serious consequence to the Subsequent System (e.g., the attacker cannot disrupt existing connections, but can prevent new connections; the attacker can repeatedly exploit a vulnerability that, in each instance of a successful attack, leaks a only small amount of memory, but after repeated exploitation causes a service to become completely unavailable).

Definitions: FIRST CVSS v4.0 specification.

Exploitation evidence

Disclosed: evidence found.
CVE published 30 Jul 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: evidence found.
1 Metasploit module
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 29 Oct 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 activestorage to 7.2.3.2; activestorage to 8.0.5.1; activestorage to 8.1.3.1.

Affected software

Product	Affected	Fixed in
RubyGemsactivestorage	Affected <7.2.3.2	Fixed in 7.2.3.2
RubyGemsactivestorage	Affected >=8.0.0.beta1 <8.0.5.1	Fixed in 8.0.5.1
RubyGemsactivestorage	Affected >=8.1.0.beta1 <8.1.3.1	Fixed in 8.1.3.1

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

Description

### Impact In its default configuration, a Rails application that displays image variants may allow an unauthenticated attacker to read arbitrary files from the server, including the process environment. That environment typically holds `secret_key_base` and often credentials for external systems, which may in turn allow escalation to remote code execution or lateral movement to those systems. ### Details libvips reads and writes file formats through "loaders" and "savers" (or more generally "operations"), many of which are backed by third-party libraries. It marks some of these operations as "unfuzzed", meaning they are unsafe for untrusted content, and several handle formats unrelated to web images. Active Storage did not disable the unfuzzed operations, so an attacker who can upload a crafted file and cause a variant to be generated from it may be able to invoke one. We are aware of a mechanism by which an attacker, by uploading a crafted file, is able to cause disclosure of the contents of arbitrary files accessible on the filesystem of the targeted application. One specific attack chain has been reported to us (see "Disclosure" below), but we do not assume it is the only one that exists. ### Affected applications An application is affected if it meets all of these requirements: - Uses libvips for Active Storage image processing. This is `config.active_storage.variant_processor = :vips`, which `load_defaults 7.0` set and no later default has changed. - Allows image uploads from untrusted users. Generating variants is not a separate requirement. ### Mitigation - Upgrade to a fixed version of `activestorage`. - The minimum version of libvips must be upgraded to `>= 8.13`. - Change `secret_key_base` and change any secrets accessible in the application environment (see "Expire and change secrets" below) Earlier versions of libvips (`< 8.13`) cannot disable unfuzzed operations at all, and Active Storage will raise an exception during boot in such an unsecurable environment. ### Expire and change secrets Upgrading closes the vulnerability but does not undo an exfiltrated secret if that already occurred. An affected application should treat every secret readable by the application process as potentially exposed and change it, including: - `secret_key_base` - The master key, whether stored in `config/master.key` or supplied as `RAILS_MASTER_KEY`, along with everything in `config/credentials.yml.enc` that it decrypts - Credentials for the Active Storage service, such as S3, GCS, or Azure keys - Database credentials - Tokens and keys for any third-party service the application calls Changing `secret_key_base` expires active sessions and requires users to log in again. Encrypted cookies, signed cookies, signed global IDs, and Active Storage URLs are also affected. Rotation should only be used as an intermediate step if necessary. Do not retain an exposed secret as a fallback. ### Workarounds If libvips `< 8.13` is being used, there are no workarounds available other than removing the dependency on libvips from the application. Some applications may have `ruby-vips` declared as a dependency only for image analysis, and those applications may be able to simply remove `ruby-vips` from the Gemfile to remove libvips from the application. Applications that do not use Active Storage can remove `ruby-vips` from the Gemfile to avoid the boot-time checks. If libvips `>= 8.13` is present on the system, applications can disable the unfuzzed operations without upgrading Rails by setting the `VIPS_BLOCK_UNTRUSTED` environment variable, which libvips reads while initializing. Applications also running ruby-vips `>= 2.2.1` or later can instead call `Vips.block_untrusted(true)` from an initializer. ### Releases The fixed releases are available at the normal locations. ### Versions affected - activestorage < 7.2.3.2 - activestorage >= 8.0, < 8.0.5.1 - activestorage >= 8.1, < 8.1.3.1 ### Disclosure Technical details of the attack chain are intentionally omitted from this advisory. They would add nothing to an administrator's decision to upgrade, while making it substantially easier to attack applications that have not yet done so. Details will be disclosed no later than 2026-08-28, via the [Rails Security Announcements](https://discuss.rubyonrails.org/c/security-announcements/9) forum. ### Credit This issue was responsibly reported by [0xacb](https://x.com/0xacb), [s3np41k1r1t0](https://x.com/s3np41k1r1t0) and [castilho](https://x.com/castilho101) from [Ethiack](https://ethiack.com), and [RyotaK](https://ryotak.net) from [GMO Flatt Security Inc.](https://flatt.tech/en/). ### References - libvips 8.13 release notes, [blocking of unfuzzed loaders](https://www.libvips.org/2022/05/28/What's-new-in-8.13.html#blocking-of-unfuzzed-loaders) - W.A. Arbaugh, W.L. Fithen, and J. McHugh, ["Windows of Vulnerability: A Case Study Analysis"](https://doi.org/10.1109/2.889093), IEEE Computer 33(12), December 2000 - https:/

Metasploit modules

Ruby on Rails Active Storage Vips Arbitrary File Read and Remote Code Executionexploit · Normal (opens in a new tab)

Proofs of concept on GitHub

Public PoC repositories for CVE-2026-66066 (opens in a new tab)

Public tooling indexed from Metasploit Framework, Exploit-DB, ProjectDiscovery nuclei-templates and PoC-in-GitHub. Its existence raises the odds of exploitation; it does not confirm attacks.

CWE-1188Initialization of a Resource with an Insecure Default (opens in a new tab)
Base weakness
The product initializes or sets a resource with a default that is intended to be changed by the product's installer, administrator, or maintainer, but the default is not secure.
OWASP Cheat Sheets
Forgot Password (opens in a new tab)
OWASP ASVS 4.0.3
V2.3.1 (opens in a new tab)
V2.6.2 (opens in a new tab)
V2.7.6 (opens in a new tab)
Attack patterns
Exploitation of Thunderbolt Protection Flaws (opens in a new tab)
From MITRE CWE, MITRE CAPEC and OWASP (Top 10, OpenCRE).

References

Community reviews

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Exploitation evidence

What to do

Affected software

Description

Public exploits and detection1 Metasploit module, GitHub proofs of concept

WeaknessesCWE-1188

Technical details

References

Community reviews

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