Software-as-a-Service (SaaS) is no longer an IT choice; it’s the operating system of business itself. From Salesforce to Workday, Microsoft 365 to Slack, the SaaS layer now underpins collaboration, analytics, and decision-making. Yet, while businesses enjoy the convenience, scalability, and cost-efficiency these platforms offer, many overlook the hidden web of interconnected risks beneath them. The growing sophistication of SaaS supply chain attacks – particularly those exploiting connectors and OAuth trust chains – has made this one of the most insidious and underestimated threats in cybersecurity today.
The cloud convenience that opened the door
The SaaS revolution was built on speed and accessibility, unblocking a world of potential for businesses. For example, if a business needed a new analytics tool, they could integrate it with their CRM system in minutes. If they required seamless file sharing or real-time communication, businesses could connect their apps via OAuth and move on. But this very convenience – the ability for apps to freely “talk” to one another – has become an Achilles’ heel.
Unlike traditional software, where companies maintain direct control over code and infrastructure, SaaS operates on trust. Businesses rely on a constellation of third-party applications and integrations that often have deep permissions into core systems. Enterprises connect CRM, ERP, HR, and analytics systems via OAuth, SCIM, or custom APIs to achieve automation. Yet, each interconnection introduces a bidirectional trust boundary.
Attackers now exploit this integration layer, not by breaching a vendor’s data centre, but by compromising the digital relationships between trusted apps. This form of intrusion, often invisible to SOC tools designed for endpoint or network telemetry, has given rise to SaaS supply chain compromise as a distinct kill chain.
OAuth: the double-edged sword of trust
At the heart of many SaaS integrations lies OAuth, the open standard that allows users to grant third-party apps limited access to their data without sharing passwords. It’s an elegant solution for secure delegation, but also a goldmine for attackers who understand its nuances.
Here’s how it typically happens: a malicious actor creates or compromises an application that appears legitimate. They trick users – sometimes even IT administrators – into granting OAuth permissions. Once approved, that token provides persistent, trusted access to the organisation’s SaaS environment, bypassing traditional security controls such as multi-factor authentication and endpoint protection.
What makes this particularly dangerous is that OAuth tokens often remain valid long after users change passwords or administrators revoke access elsewhere. This silent persistence can allow adversaries to exfiltrate sensitive data, move laterally between systems, or inject malicious code into software updates, all without raising immediate alarms.
When “trusted” connections turn rogue
One of the most complex challenges in mitigating SaaS supply chain attacks is visibility. Many IT teams lack a comprehensive inventory of every SaaS app connected to their environment, let alone the level of access each one has. In some cases, employees unknowingly authorise risky third-party apps through “shadow IT,” which bypasses official vetting processes.
The result? A tangled web of connectors and integrations forming what security experts now call the SaaS trust chain. Each new connection adds another link and another potential entry point for attackers. When a single link is compromised, it can cascade across multiple applications, magnifying the damage.
Imagine a compromised analytics tool injecting malicious code into a shared data environment. That data, in turn, feeds into a financial dashboard or HR system that other teams rely on. Within hours, the breach spreads across departments, and by the time it’s detected, the attacker has already accessed confidential data, email systems, and API credentials.
Building resilience: beyond the perimeter
Traditional cybersecurity models focused on perimeter defence, firewalls, endpoint detection, and network segmentation. But in a SaaS-first world, the perimeter no longer exists. The new security paradigm demands continuous visibility, zero trust, and proactive governance.
IT teams must begin by mapping their entire SaaS ecosystem. This means identifying every authorised app, understanding its permissions, and monitoring how data flows between them. Automated tools can help by providing real-time insight into third-party integrations and flagging anomalies.
Second, adopting Zero Trust Architecture (ZTA) principles is critical. This model assumes that no application, user, or connector should be inherently trusted, even those within the network. The reassurance of continuous verification, context-aware access, and the ability to revoke access at any time is a cornerstone of this model.
Lastly, incident response strategies must evolve. Because SaaS connectors operate differently from traditional endpoints, detection and response mechanisms must account for token-based access, API traffic, and integration behaviour.
Collaboration: the missing link in SaaS security
No organisation can manage the complexity of SaaS ecosystems alone. The diversity of platforms, connectors, and access models means that even the most vigilant internal teams can miss vulnerabilities hidden in third-party integrations. This is where collaboration with cybersecurity experts and managed service providers becomes invaluable.
External specialists bring deep visibility into SaaS risk posture across industries. They can identify blind spots, deploy advanced monitoring systems, and simulate supply chain attack scenarios to test an organisation’s readiness. Moreover, their broader experience allows them to recognise patterns and emerging attack tactics before they become widespread.
Partnering with experts doesn’t just add another layer of protection; it accelerates the organisation’s ability to adapt. These specialists can help create governance frameworks, design automated response protocols, and continuously assess the security of new SaaS integrations. In a threat landscape that evolves daily, collaboration ensures businesses stay a step ahead of attackers who thrive on isolation and oversight gaps.
The human layer of SaaS security
While technology plays a significant role, people remain both the weakest and potentially strongest link in SaaS security. IT professionals should implement training programmes that help employees understand OAuth consent prompts and recognise suspicious integration requests. Regular awareness campaigns can prevent well-intentioned users from inadvertently authorising malicious apps.
Security teams should also work closely with procurement and compliance departments. Too often, SaaS purchasing decisions are made without security oversight, leading to unvetted applications entering the environment. By integrating cybersecurity considerations into procurement workflows, organisations can pre-empt risks before they materialise.
Rebuilding trust, intelligently
The next generation of SaaS attacks will combine AI-generated connectors, adversarial ML models, and autonomous API exploitation. Enterprises must therefore build a resilient SaaS fabric in which visibility, automation, and governance form a continuous defensive loop.
Yet, visibility, collaboration, and vigilance must define the new cybersecurity mindset. By combining internal governance with external expertise, organisations can transform the very trust model that once made them vulnerable into a resilient, adaptive defence.
About the author: The article is authored by Avinash Gupta, Head of COE (Centre of Excellence) at In2IT Technologies.