What is CVE-2026-66066?A critical-severity flaw, explained.
CVE-2026-66066 is a critical-severity flaw (CVSS 9.5) in the software it affects, published on 30 July 2026. It is not on the list of flaws known to be exploited today. The latest forecast puts its chance of use in the next 30 days at 28%. If you run an affected version, plan in the vendor’s fix.
Published 30 July 2026. Record last updated 10 September 2026. We keep this page's data up to date.
What is CVE-2026-66066? In plain terms.
It can be attacked from anywhere on the internet without logging in, and nobody has to click anything.
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.
What kind of flaw is it?
- CWE-1188Initialization of a Resource with an Insecure Default
How an attack on it works
Read straight from its severity rating, translated out of the shorthand.
- Where an attacker can beAnywhere on the internet
- How hard it is to pull offEasy: no special conditions
- Login needed firstNo login needed
- Does someone have to clickNo, nobody has to do anything
Severity vector: 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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Is CVE-2026-66066 being exploited? Not that we know of.
It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 28%. That can change at any time, which is why we keep watching.
Timeline
- Published
- Exploit likelihood jumped
- Record last updated
- Exploit likelihood fell
CVE-2026-66066 scores 56. Action: Plan remediation.
We keep the score of every published flaw up to date as the evidence changes. Four things go into the score, and evidence that criminals are actually using it counts most. In order:
- Evidence it is being exploitedBiggest factor
- How severe it isStrong factor
- How widely exposed it isSmaller factor
- Threat activity around itSmaller factor
85 and above is Critical. Anything confirmed as exploited is always marked for an emergency patch, whatever its score.
When CVE-2026-66066 matches software you track, it lands in your list with its score and the reasons behind it.
See your own ranked list →Who is affected by CVE-2026-66066? 0 products.
Here is what the published record lists as affected.
No affected products have been listed for this flaw yet. That usually means the record is still being analysed.
How do I fix CVE-2026-66066? Four steps.
- Check whether you run itCompare your versions with the affected products above. Not sure what you run? Precursor Intelligence can work it out from your public website, or you can pick it from a list.
- Apply the vendor’s fixInstall the latest update from the vendor. The references list where the vendor has published details.
- If you can’t patch todayFollow any mitigation the vendor publishes, and limit who can reach the affected system from the internet until the update is in.
- Keep an eye on itTrack the product and we tell you as soon as we spot this flaw on the list of exploited flaws, or a jump in its exploit likelihood.
References
13 linksDoes CVE-2026-66066 affect you? We'll keep checking.
Looking flaws up one at a time doesn't scale. Tell us what you run once, and we tell you which flaws matter to you, in what order, and keep watching for new ones.
- Tell us what you runPick your software from a list, or let us work it out from your website.
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1 new flaw affects software Acme tracks
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 li...
- Matched to
- Your software on Acme's software list
- What to do
- Plan in the vendor’s update
Sent to the alert recipients Acme chose. Also in the app and to Acme's webhook.
CVE-2026-66066 is a critical-severity flaw in the software it affects, published on 30 July 2026. It can be attacked from anywhere on the internet without logging in, and nobody has to click anything.
It scores 9.5 out of 10 on the CVSS severity scale, which is critical. Our risk score for CVE-2026-66066 is 56 out of 100, which is Medium. Its action is "Plan remediation". Not confirmed as exploited yet, but serious or likely enough that it should not wait for a quiet month.
It is not on the list of flaws known to be exploited today. The latest forecast puts the chance of it being used in the next 30 days at 28%. That can change at any time, which is why we keep watching.
Install the update the vendor names in its advisory. If you can't patch today, follow the vendor's mitigation and limit who can reach the affected system from the internet.