What is the CMID cookie?
Identifies a browser/user for Index Exchange's advertising exchange so it can match audiences and help deliver targeted ads through programmatic real-time bidding.
Table of Contents
About CMID
| Vendor | Index Exchange |
|---|---|
| Cookie Domain | casalemedia.com |
| Category Category The functional category of the technology, such as Web Analytics or Social Media. Learn more | Site Infrastructure & Security |
| 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 | 1 yr |
| 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 | High |
| Vendor Privacy Policy | https://www.indexexchange.com/privacy/ |
| Vendor Website | https://www.indexexchange.com/ |
What is the purpose of CMID?
The CMID cookie is a third-party tracking cookie set by Index Exchange (formerly Casale Media, rebranded in 2015) through their programmatic advertising platform. It functions as a unique browser identifier that allows the platform to recognize users across various publisher domains within its ad exchange network. This identifier is essential for cross-site tracking, enabling demand-side platforms (DSPs) to map the user to their own identity graphs via user matching and syncing mechanisms.
By maintaining this persistent ID, Index Exchange facilitates real-time bidding (RTB) and programmatic ad delivery. It allows advertisers to evaluate ad inventory, deliver personalized and targeted advertisements based on behavioral profiles, frequency-cap ad campaigns, and perform ad measurement and attribution. The cookie is typically set to expire after one year and is refreshed each time the user interacts with a participating publisher's digital property.
What are the Privacy Risks of CMID?
Risk Level: High
The CMID cookie is a persistent, third-party identifier explicitly designed for cross-site tracking, audience profiling, and targeted advertising. It enables multiple independent entities within the programmatic ad tech ecosystem (including demand-side platforms and data brokers) to synchronize user profiles and share behavioral data. Because it actively facilitates the compilation of extensive browsing histories across unrelated websites to target personalized ads, it carries a high privacy risk and generally requires explicit user consent under privacy frameworks like GDPR and CCPA.
How to Remove CMID from a Website
To remove the CMID cookie, the website operator must remove the Index Exchange integration that sets it. In practice this means removing the Index Exchange tag/script or the Index Exchange programmatic bidding adapter (e.g., the IX bidder in a Prebid.js / header-bidding configuration) from the site's source code or tag management system, or removing Index Exchange from the list of active bidders in the header-bidding wrapper. Because CMID is set by Index Exchange's exchange platform as part of its core user-matching and ad-delivery function, it cannot be disabled independently of the service - if the publisher relies on Index Exchange for monetization, the cookie can only be eliminated by removing the Index Exchange integration entirely. If only a specific Index Exchange feature is in use, the operator can also contact Index Exchange to adjust account-level configuration.