What is the CMPRO cookie?
CMPRO is an HTTP cookie placed by Casale Media, an ad-tech company that owns and operates Index Exchange, one of the largest programmatic advertising exchanges in the world.
The cookie is not set directly by the website owner but by a third-party script or bid request loaded as part of the site's advertising supply chain — typically through Prebid.js, Google Ad Manager, or other SSP/DSP integrations connected to Index Exchange. It usually appears on the first load of a page containing ad slots served through this ecosystem.
What data it stores
CMPRO generally stores a randomly generated unique identifier used to recognize the browser on subsequent visits to any site participating in the Index Exchange network. The exact value format is not publicly documented and may vary.
The data associated with this identifier is sent to Casale Media/Index Exchange servers and may be combined with information about pages visited, device type, and ad interactions to build an advertising profile.
What it is used for
Its main purpose is cookie syncing/matching between the various parties in the programmatic advertising chain — publishers, agencies, and ad exchanges — so they can recognize the same user across different platforms.
For the publisher showing the ads, this cookie helps increase the price obtained per impression through better-targeted bidding; for Casale Media, it helps build behavioral profiles used for ad targeting.
Does it require consent?
CMPRO falls under the marketing/advertising category in CookieFix's classification. It is not strictly necessary for the site to function; it exists solely for targeted advertising and cross-site tracking purposes.
- Under GDPR (Regulation 2016/679) and the ePrivacy Directive, this cookie requires prior consent from the visitor before being set.
- The site owner must disclose it in the cookie policy, listing the provider (Casale Media/Index Exchange), its purpose, and its duration.
- The script that triggers it must be technically blocked until the visitor accepts the marketing category.
How to block or delete CMPRO
A visitor can delete the CMPRO cookie from browser settings (Chrome, Firefox, Edge, Safari — cookies and site data section) or block third-party cookies through privacy settings. Ad/tracker-blocking browser extensions can also prevent it from being set.
For site owners, blocking must happen before consent is given, not just removal afterward. A consent management platform (CMP) like CookieFix can automatically block scripts that trigger CMPRO-type cookies until the visitor consents to the marketing category.
Frequently asked questions
It is not technically harmful, but it is a tracking cookie used for targeted advertising and cross-platform identifier sharing, which is why it requires consent.
It is set by Casale Media, the company behind the Index Exchange programmatic ad exchange, typically via a third-party script included in the site's ad supply chain.
The typical observed duration is around 3 months, after which it expires automatically.
Yes, since it is a marketing cookie requiring consent under GDPR and ePrivacy, it must be explicitly disclosed with its provider, purpose, and duration.