What is CVE-2026-66066?

CVE-2026-66066 is Action Pack: Possible arbitrary file read and remote code execution in Active Storage variant processing. The supplied enrichment data classifies it as Remote Code Exec mapped to CWE-1188 CWE-1188.

Which versions are affected?

Affected product and version evidence is listed in the product table above. Current public advisories should be checked for exact version scope before patch targeting is finalized.

Is there active exploitation?

Active exploitation is not confirmed from current sources for CVE-2026-66066. If exploitation is not confirmed from current sources, teams should document that status and continue monitoring KEV, vendor, and telemetry updates.

No. CVE-2026-66066 is not listed in CISA KEV in the supplied enrichment data. KEV status should be monitored because it can change after initial disclosure or after exploitation becomes publicly confirmed.

Is there a public exploit?

11 public PoC repositories reported; 2 marked weaponized in current dataset. Public exploit or PoC availability should raise triage priority, especially for exposed or business-critical systems.

How can defenders detect it?

Start with web/proxy/WAF logs, application logs, network IDS/IPS, EDR process telemetry, host service logs where available. Look for vulnerability-class behavior, product errors, suspicious authentication events, exploit probes, and abnormal process activity based only on evidence that applies to the affected product.

How should teams prioritize it?

Prioritize CVE-2026-66066 using CVSS 9.5, EPSS 28%, KEV status, public PoC status, and asset exposure. Internet-facing, privileged, or business-critical deployments should be handled first.

Are workarounds available?

The supplied mitigation guidance says to apply vendor patches and restrict external exposure until fixed. Fixed-version evidence is listed in the mitigation section above.

Which threat actors are linked publicly?

No public threat actor linkage is confirmed from current sources. Do not attribute exploitation to a threat actor unless the source evidence explicitly supports that linkage.

What should be done in the next 24 hours?

Identify exposed assets running affected vendor/product/version combinations. Prioritize based on EPSS, PoC availability, and external exposure. Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class. Open remediation tickets with affected assets, owners, evidence status, and detection coverage so decisions are traceable.

criticalRemote Code Execpublic exploit

CVE-2026-66066

CVE-2026-66066 — Action Pack: Possible arbitrary file read and remote code execution in Active Storage variant processing

Action Pack is a framework for handling and responding to web requests. In versions prior to 7.2.3.2, 8.0.5.1 and 8.1.3.1, Active Storage does not disable libvips operations marked unsafe for untrusted content, allowing a crafted upload to invoke such an operation. Consuming applications are affected when configured to use libvips and accept image uploads from untrusted users. An unauthenticated attacker may exploit this behavior to read arbitrary files accessible to the Rails process, including environment variables and application secrets. Exposure of credentials such as secret_key_base or external-service tokens may enable remote code execution or lateral movement. This issue has been fixed in versions 7.2.3.2, 8.0.5.1 and 8.1.3.1.

Published Jul 30, 2026Updated Aug 5, 2026Sources: NVD, rails (CNA), Red Hat (VEX), SOCRadar CTI

Triage

Is it exploited, how likely is exploitation, what does it touch, and how severe do the scoring sources call it.

Exploitation

Exploit code

public exploit, none observed

EPSS

28%

ahead of 98% of scored CVEs

Affects

rails

3 products listed

CVSS base

9.5

critical · 2 sources

CISA SSVC assessment

Three decision points CISA publishes for the CVEs it assesses · SSVC 2.0.3. A stakeholder decision, not a severity score.

CISA

Exploitation

PoC

none · proof-of-concept · active

Automatable

Yes

can an attacker script all four kill-chain steps

Technical impact

Total

partial · total control of the vulnerable component

Remediation

The vendor's own words where we have them.

Upgrade rails to a fixed release. Apply vendor patches per advisory and restrict external exposure of the affected component until patched.

Red Hat VEX · CVE-2026-66066

fixed0affected0not affected19

First 24 hours

Ordered from the record's own fields — exposure first, because you cannot patch what you have not found.

Identify exposed assets running affected vendor/product/version combinations.
Prioritize based on EPSS, PoC availability, and external exposure.
Search available logs for exploit probes, errors, authentication anomalies, or suspicious child processes matching the vulnerability class.

Affected scope

Vendor, product and version as the advisories word them.

Vendor	Product	Versions	Status
rails	rails	< 7.2.3.2	Vulnerable
rails	rails	>= 8.0.0.beta1, < 8.0.5.1	Vulnerable
rails	rails	>= 8.1.0.beta1, < 8.1.3.1	Vulnerable

Attack characteristics

The CVSS vector, decoded. It describes the attack, not your exposure to it.

Scope

Attack Complexity

Low

Attack Vector

Network

Privileges Req

None

User Interaction

None

Every base score collected

Sources score independently and disagree; each row says who scored it and under which version.

Score	Version	Severity	Expl.	Impact	Source
9.5	CVSS 4.0	critical	—	—	rails (CNA)
8.9	CVSS 3.1	high	—	—	Red Hat (VEX)

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

Weakness & attack patterns

CWE-1188

Inferred from the weakness class — not observed against this CVE.

CAPEC-242 · Code InjectionCAPEC-35 · Leverage Executable Code in Non-Executable Files

T1211Exploitation for Defensive Evasion
T1542.002Pre-OS Boot: Component Firmware
T1556Modify Authentication Process

Public exploit

Capability, not use: code existing is a different claim from anyone running it.

Repositories

2 of the 5 sampled are weaponized

Exploit entries

Exploit-DB and CTI exploit indexes

Social mentions

Posts naming this CVE. Attention, not evidence of exploitation — it spikes on disclosure and decays whether or not anything is exploited.

35 more posts on this CVEShowing 5 of 40 · Who is discussing this CVE, and how loudlyUnlock free

Detection

Read off the CVSS vector and the weakness class. Starting points, not rules we have tested.

Prioritize edge telemetry for network-reachable rails.
Monitor for scanner or exploit-pattern traffic after 11 public PoC repositories were reported.

web/proxy/WAF logsapplication logsnetwork IDS/IPSEDR process telemetryhost service logs

Timeline

What happened to this CVE, newest first — with the readings a source repeats on a schedule counted underneath rather than listed.

2026
Added · CVSS 3.1 9.5 (AV:N)
Aug 5, 2026 · NVD
Cve is exploited HackSpeak/CVE-2026-66066
Aug 4, 2026 · SOCRadar CTI
Cve is exploited HackSpeak/kindarails2shell-poc
Aug 3, 2026 · SOCRadar CTI
Initial · CVE published
Jul 30, 2026 · NVD

Source activity

Readings a source repeats on a schedule, counted rather than listed.

15×TweetsAug 1, 2026 – Aug 29, 2026 · SOCRadar CTI
15×SVRS was changedAug 1, 2026 – Aug 29, 2026 · SOCRadar CTI
4×Github ReposJul 31, 2026 – Aug 4, 2026 · SOCRadar CTI
3×CVE modified by MITRE: CVSS metrics updated.Jul 31, 2026 – Aug 4, 2026 · SOCRadar CTI
1×1 time mentioned on 1 Telegram channelAug 1, 2026 · SOCRadar CTI

References

17 on the record

github.com/rails/rails/commit/1c01bb587206ee6eb0e1179c2cef96a6a47acb1e
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/commit/349e7a5d5b4b715af1e416db824f3c078a7d59e5
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/commit/d79b7f4aa17dec8ce4960fef05733c8c0c7ef49a
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/releases/tag/v7.2.3.2
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/releases/tag/v8.0.5.1
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/releases/tag/v8.1.3.1
Exploit, Third Party Advisory, Mitre, NIST
github.com/rails/rails/security/advisories/GHSA-xr9x-r78c-5hrm
Exploit, Third Party Advisory, Mitre, NIST
github.com/rubysec/ruby-advisory-db/blob/master/gems/activestorage/CVE-2026-66066.yml
Exploit, Third Party Advisory, Mitre, NIST

Coverage

18 stories from the feeds we poll

13 more reports on this CVEShowing 5 of 18 · Vendor research and security press coverageUnlock free

Elsewhere on this site

railsevery CVE for this vendor
Remote Code Execsame class
CWE-1188other pages naming this weakness

Not in any source we poll

Listed rather than left blank: an empty field and an unmeasured one look identical on screen, and only one is a reason to look elsewhere.

No confirmed IOCs, IP addresses, domains, file hashes, or malware artifacts supplied.
No organization-specific asset inventory, compensating-control status, or patch deployment evidence supplied.
No exploit packet captures, log samples, or incident case IDs supplied.

Answered from this record1

What should defenders know first?

CVE-2026-66066 is Action Pack: Possible arbitrary file read and remote code execution in Active Storage variant processing, a critical vulnerability affecting rails from rails. The current evidence does not list it in CISA KEV, and the exploit status is: Active exploitation is not confirmed from current sources for CVE-2026-66066. Public exploit evidence is: 11 public PoC repositories reported; 2 marked weaponized in current dataset. The affected-version evidence is listed in the key facts and affected products tables. Defenders should first verify whether exposed or business-critical assets run those versions, then apply vendor patches or mitigations, restrict reachable attack surface, and preserve logs for detection review. CVSS 9.5 describes technical severity, while EPSS 28% helps estimate near-term exploit likelihood; neither replaces asset context. Unknown fields should remain explicit in tickets, and threat actor, IOC, victimology, or payload claims should not be added unless a cited source supports them. Monitor CISA KEV, vendor advisories, NVD changes, public PoC repositories, and internal telemetry for update triggers.