What is an SSL stripping attack and how to prevent it
SSL stripping is a man-in-the-middle attack that downgrades secure HTTPS connections to HTTP, exposing sensitive user data. This article explains how the attack works and outlines the best technical and strategic measures businesses and users can take to defend against it, such as HSTS enforcement, certificate transparency, and automated certificate management.
Hypertext Transfer Protocol Secure (HTTPS) plays a crucial role in every online interaction. Without it, digital communication would not be nearly as safe, nor would users enjoy any semblance of peace of mind.
This protocol has an extremely important job: encrypting data as it moves between browsers and web servers. This prevents malicious parties from intercepting information — but this only works if an HTTPS connection is successfully established and maintained.
One serious threat to HTTPS connections is a tactic known as SSL stripping. Commonly unleashed during man-in-the-middle (MiTM) attacks, SSL stripping downgrades connections to an unencrypted Hypertext Transfer Protocol (HTTP) version without user awareness, making it easier for bad actors to intercept confidential data, including everything from login credentials to credit card information. Meanwhile, users assume that their sessions are secure when in reality they are not.
Thankfully, this type of attack is far from inevitable. Despite the covert nature of the SSL stripping tactic, several preventative measures can stand in the way of downgrade attacks. Keep reading to learn what this harmful technique involves and what it takes to prevent both SSL stripping and man-in-the-middle attacks.
SSL stripping meaning and overview
The term 'SSL stripping' is used to describe a specific type of man-in-the-middle strategy in which the attacker downgrades an HTTPS connection. The use of 'SSL' in this term describes the effort to remove (or 'strip' away) the Secure Sockets Layer (SSL) certificate that forms the basis for HTTPS in the first place. Although "SSL" appears in the term, most modern secure communications use Transport Layer Security (TLS), the successor to SSL. The term SSL stripping remains common for historical reasons.
No matter its name, SSL stripping follows a few basic steps: interception, downgrading, impersonation, and deception. The ultimate goal is to encourage users to submit sensitive data via insecure connections. While the user may not immediately be wise to this form of tampering, it can spark long-term damage, including not only immediate concerns involving compromised data, but also, undermined trust in the long run — and eventually, reputational damage.
How an SSL stripping attack works
SSL stripping attacks begin with the unsuspecting user's efforts to visit an HTTPS site that, at first glance, seem secure. Attackers can intercept these requests by placing themselves between users and the websites they intend to visit.
Often, this involves compromised routers, although unsecured WiFi networks can also open the door to SSL stripping. Attackers may use sophisticated strategies such as ARP (Address Resolution Protocol) spoofing to send falsified messages within local networks. If this strategy is successful, the user's device will regard the attacker's machine as legitimate.
The MiTM positioning of the attacker can also be achieved via DNS (Domain Name Service) spoofing. DNS spoofing shares much in common with ARP spoofing but shifts its focus to the application layer and the DNS system, as opposed to ARP's local networks. This type of manipulation allows attackers to intercept DNS queries and return incorrect IP addresses.
Once the attacker is in position, the SSL stripping attack unfolds through a predictable sequence:
The user attempts to connect to a secure HTTPS site.
The attacker intercepts the initial request and silently redirects the user to an unencrypted HTTP version.
To avoid raising suspicion, the attacker maintains the HTTPS connection with the legitimate server in the background.
Meanwhile, all data sent by the user, including logins, credit card numbers, or other personal information, is exposed in plaintext and can be read or modified by the attacker.
Because this attack relies on silent redirection, users often continue browsing without realizing anything is wrong. The page may look completely legitimate, while their personal data is being intercepted in real time.
How to prevent SSL stripping attacks
Based on the step-by-step process described above, a few key risk factors for SSL stripping should be evident: issues with routers and WiFi connections. While users can safeguard their information by addressing these common concerns, businesses also have a responsibility to implement protective measures.
There are many ways to accomplish this, and ideally, businesses will use a layered approach that takes the many forms of SSL stripping into account. These solutions typically fall into one of two main categories: technical or strategic. Both are critical for the purposes of SSL stripping prevention and for protecting users as they interact online.
Technical best practices
Technical strategies form a strong starting point for preventing MiTM attacks and especially SSL stripping. Some of these best practices require more expertise than others, but all are worth considering in the effort to provide well-rounded protection:
Implement HTTP Strict Transport Security (HSTS): Specifically designed to prevent SSL stripping and MiTM attacks, HSTS ensures that browsers always use HTTPS. This relies on headers with the Strict-Transport-Security directive, ensuring not only that browsers connect exclusively via secure HTTPS connections, but also, limiting the amount of time that these connections last so that even if downgrades are attempted, the browser ultimately continues to enforce HTTPS. Browsers will block HTTP fallback if HSTS is configured correctly.
Use server-level enforcement: Measures can be implemented on servers to facilitate secure communication between servers and clients. The foundation for server-level enforcement involves strong SSL/TLS certificates, ideally avoiding the use of weak encryption protocols.
Monitor certificates with Certificate Transparency (CT): Certificate Transparency creates a public log of all certificates issued for a domain, helping organizations quickly detect and respond to fraudulent or misissued certificates. Unlike certificate pinning, CT provides visibility and accountability without the operational risks. Monitoring CT logs allows organizations to quickly identify and respond to unauthorized SSL certificates before they can be exploited.
Business best practices
In addition to sophisticated technical strategies, it is important to adopt policies and protocols that address the big-picture issues that contribute to SSL stripping. Essentials include:
Make the most of automated solutions: Manual certificate management strategies increase susceptibility to many types of attacks, including SSL spoofing and MiTM. IT departments work hard to keep up but cannot possibly handle the sheer volume of certificate renewals — especially as certificate lifespans continue to shrink. This is where automated certificate lifecycle management (CLM) solutions such as Sectigo Certificate Manager (SCM) can prove invaluable. Automation limits the burden on IT professionals, who, instead of manually renewing certificates after just a few weeks, can focus on other important concerns.
Keep up to date with SSL/TLS protocols: New versions of TLS are frequently unveiled to ensure that encryption standards remain strong and that attackers are unable to exploit known vulnerabilities. Businesses should make the most of these updated protocols by frequently reviewing cryptographic recommendations. Always use trusted CAs, as these offer not only robust MiTM protection, but also, help prevent common misconfigurations.
Continue to update and audit security configurations: Strategies that currently seem effective may not prove sufficient as attackers continue to develop more sophisticated and difficult-to-combat strategies for accessing users' confidential information. Therein lies the need for frequent assessments, which can reveal existing weaknesses, ideally long before they are exploited.
Why this type of attack is a serious security threat
SSL stripping represents a huge threat to both users and businesses. Not only does this technique lead to intercepted data, it also limits users' ability to combat man-in-the-middle attacks — after all, users cannot defend themselves effectively against threats when they're entirely unaware that these hazards exist.
From the enterprise's perspective, this undermines trust while limiting the efficacy of seemingly well-designed cybersecurity solutions. Reputational damage, customer churn, and the financial costs of breach response can escalate quickly. This could have huge ramifications that may even spark major compliance concerns. For this reason, businesses must be proactive about preventing SSL stripping and other MiTM strategies.
Protect your website against SSL stripping with Sectigo
Preventing SSL stripping begins with strong encryption, and that means trusting a proven Certificate Authority to protect your users and your brand.
As you adopt robust strategies for reducing the risk of SSL spoofing and MiTM attacks, don't underestimate the value of highly trusted SSL/TLS certificates. These are responsible for enabling HTTPS and providing the encryption and authentication upon which secure digital communication depends. As an industry-leading CA, Sectigo has a strong reputation and offers several solutions designed to meet evolving enterprise security needs.
Offering SSL/TLS certificates at several validation levels (including Domain Validation, Organization Validation, and Extended Validation certificates), Sectigo equips businesses with the fundamental tools and resources needed to make the most of HTTPS.
Using a trusted CA is only the beginning. To ensure prompt certificate renewals and full compliance, make the most of Sectigo Certificate Manager. This CA-agnostic CLM solution provides a centralized dashboard and automated workflows designed to simplify and streamline the entire certificate lifecycle. This automated solution helps to prevent outages, improves user trust, and even supports compliance. Get started today with a demo or a free trial.