Shadow IT discovery: identifies cloud applications used without IT approval. Reports show popular apps, involved users, sensitive data transferred.
What is CASB
CASB (Cloud Access Security Broker) is a security platform that monitors, controls and protects user access to cloud applications (SaaS, IaaS, PaaS). It implements visibility of shadow IT (unauthorized applications used by employees), policy-based access control, cloud malware detection, and data loss prevention (DLP). CASBs act as a proxy between users and cloud services to inspect traffic, authenticate, authorize, and generate alerts about anomalous behavior or policy non-compliance.
Why it matters
Cloud-first trends and remote work have accelerated SaaS adoption (messaging, CRM, productivity suites, shared storage) without central oversight. CASB closes a critical gap: when an employee falls back on personal cloud storage, uses a non-corporate email account or accesses SaaS with a compromised credential, CASB detects it and enforces policy. Without CASB, security teams have minimal visibility into what cloud apps employees actually use. Regulations such as ISO 27001 require access control to external systems; NIS2 and DORA add cloud visibility and third-party governance on top. Attacks on SaaS are frequent: credential compromise, phishing targeting cloud users, weak configuration (publicly shared drives) and data theft. CASB combined with corporate directory integration and MFA is essential defence for containing that risk.
Key points
Data Loss Prevention (DLP): monitors data transfer to cloud; blocks if file contains sensitive data (credentials, PII, trade secrets).
Directory integrations: syncs users, groups and permissions from the corporate directory (LDAP, Active Directory, cloud identity providers); revokes access automatically if user is terminated or role changes.
Cloud threat detection: identifies malware, anomalous behavior (login from impossible location, massive download), and APT activity targeting SaaS.
Example: Shadow IT exposes data in personal cloud storage
A marketing manager starts using a personal cloud storage account to share product presentations with an external agency, because it feels faster than the internal process. Without CASB, IT has no visibility of that transfer. The personal account has a weak, reused password; an attacker gets in, downloads the deck for a launch planned for the following semester and sells it to a competitor. The impact —loss of competitive advantage and IP leakage— only surfaces when it is already too late to prevent.
With CASB in place the flow changes: the platform automatically detects the personal-storage usage (shadow IT), alerts when a file tagged as confidential is uploaded to that account, enforces the policy that blocks those destinations and opens a ticket for the security team. That technical step only pays off when paired with governance work: publishing approved corporate alternatives with DLP, categorising SaaS into "approved / tolerated / prohibited", integrating the CASB with the identity directory and with the SIEM, and communicating with users so the restriction lands as a safer channel rather than a bottleneck.
Common mistakes
- Assuming firewall + traditional web proxy protects cloud; CASB inspects SaaS applications using HTTPS/TLS; traditional proxy does not decrypt SaaS.
- Implementing CASB but not integrating with directory/MFA; CASB policies not synced with user changes (late termination, old role) = gaps.
- Not configuring DLP correctly; CASB lets sensitive data transfers through if policies do not define what is sensitive (PII patterns, keywords, data classification).
Related services
This concept may be related to services such as:
Frequently asked questions
What is the difference between CASB and CSPM
CASB monitors user access to SaaS applications (control sessions, detect malware, DLP). CSPM (Cloud Security Posture Management) audits cloud infrastructure configuration (public storage buckets, weak IAM permissions, encryption at rest). Both are complementary: CASB = access protection; CSPM = configuration hardening.
Can a CASB block cloud applications
Yes. A CASB can block by policy: if a personal storage service is not authorised, access to that domain is denied. But it must act with nuance: if users legitimately rely on a given service for work, a blanket block breaks collaboration. The point is to categorise apps (approved, tolerated, prohibited) and tune policy with real context of use.
Does CASB replace VPN in remote work
No. VPN encrypts traffic between user and corporate network. CASB protects direct SaaS access. Modern architecture: Zero Trust Network + MFA + CASB + DLP. User authenticates, connects to zero-trust network, CASB monitors SaaS access and blocks sensitive data transfers.