What is the CMPRO cookie?
The CMID cookie is a unique identifier used by Index Exchange to recognize a user's web browser across different sites and servers for the delivery of targeted advertising.
Table of Contents
About CMPRO
| Vendor | Index Exchange |
|---|---|
| Cookie Domain | casalemedia.com |
| Category Category The functional category of the technology, such as Web Analytics or Social Media. Learn more | Advertising & Paid Media |
| Consent Category Consent Category The consent category this cookie most commonly falls under across sites we scan, normalized into four standard categories. Learn more | Targeting & Advertising |
| Prevalence | Very Common |
| Popularity Popularity Popularity is calculated from our dataset of 4.5B+ cookies analyzed across hundreds of millions of web pages. Learn more | Found on 21.4% of scanned pages |
| Expiration Type | Timestamp |
| Expiration Duration | 29 days |
| Party Type Party Type Whether the cookie is first-party or third-party. Learn more | 3rd-Party |
| Risk Level Risk Level Rates how sensitive the data stored by this cookie is (High, Medium, or Low) based on data classification and distribution. Learn more | Medium |
| Vendor Privacy Policy | https://www.indexexchange.com/privacy/ |
| Vendor Website | https://www.indexexchange.com |
What is the purpose of CMPRO?
The CMPRO cookie is a third-party advertising cookie set on the casalemedia.com domain by Index Exchange (the ad-technology company formerly known as Casale Media, which rebranded to Index Exchange in 2015). Index Exchange operates a global digital advertising marketplace/exchange that hosts real-time bidding (RTB) auctions connecting publishers and demand-side partners. Cookies on the casalemedia.com domain, including the CMxxx family (e.g., CMID, CMPS, CMSC), are used to associate a pseudonymous identifier with a browser/device so that Index Exchange and its partners can recognize the user, sync cookie IDs across ad-tech partners, and select and deliver relevant advertising.
According to widely published cookie catalogs, CMPRO is used for anonymous user tracking and targeted advertising, collecting non-personally-identifiable data associated with the user's browsing for the purpose of ad delivery. The observed values are short numeric integers and the cookie is served overwhelmingly (~97%) as a third-party cookie with a 60-90 day lifetime, consistent with a persistent advertising/identity-matching role rather than a first-party functional purpose. Note that no Index Exchange vendor page explicitly naming CMPRO could be verified, so the specific stored value semantics are inferred from third-party documentation and the vendor's general platform behavior.
What are the Privacy Risks of CMPRO?
Risk Level: Medium
The CMPRO cookie presents a Medium privacy risk because it is a third-party identifier set by an advertising exchange and is used to recognize a browser across sites and to participate in cookie syncing with demand-side partners and other buyers. While Index Exchange states the cookie does not carry directly identifying Personally Identifiable Information (no name, email, or address), the identifier is pseudonymous and enables cross-site recognition, audience matching, and programmatic ad delivery. Behavioral/cross-site tracking that goes beyond strictly necessary site functionality.
The observed initiator requests confirm this profiling context: they carry external_user_id values exchanged with partners such as Amazon, Outbrain, and Google. This is consistent with the cookie being categorized under Targeting/Advertising consent categories on real-world deployments, which is why it does not qualify as Low risk, but it is not High because the cookie does not by itself transmit directly identifying PII.
How to Remove CMPRO from a Website
To remove this cookie, a website administrator must locate and remove the Index Exchange integration from the site - for example, the Index Exchange tag, Prebid.js/header-bidding wrapper configuration, or any related ad-monetization scripts loaded via the source code or Tag Management System (TMS). Because CMPRO is set on Index Exchange's own casalemedia.com domain as part of its advertising-exchange demand integration, it cannot be disabled individually while continuing to use Index Exchange; removing the vendor's integration entirely will stop the cookie from being set (and will also stop ad delivery through Index Exchange). If ongoing use of Index Exchange is required, the administrator would need to contact Index Exchange to discuss any account-level configuration options.