What is Web Cache Poisoning, and How Does It Work?

Attackers often target Domain Name Systems (DNS) to poison or corrupt the DNS with wrong information, leading to web cache poisoning. According to recent reports, researchers discovered web cache poisoning vulnerabilities in many sites. This article will explore web cache poisoning, how it occurs, and the risks associated with DNS or web cache poisoning.

What are Domain Name System (DNS) and web cache poisoning?

A domain name system (DNS) is an internet phonebook or naming database that is responsible for mapping internet domain names with their respective Internet Protocol (IP) addresses. All internet users require domain names to visit the pages they are searching for. It is the DNS that redirects users to specific IP addresses. 

For example, a user may want to visit Google and will type the www.google.com string in the address bar of the browser. The request will go to the DNS server, checking whether the URL string is valid or exists in its database. Once the map matches an IP address, in this case, it will be 8.8.4.8 or 8.8.8.8—it will send a request to the server. The server will respond by displaying the page to the client.

What is DNS caching?

DNS caching is a local, device-specific copy of the DNS servers’ records. Keeping a local copy of the DNS lets the browser load the requested page quickly. A DNS resolver delivers the user with the IP address for a particular domain name. DNS caching will temporarily save the responses to IP address queries in a cache. But DNS caching does not only occur at the web browser or OS level.

What is web cache poisoning or DNS poisoning, or DNS cache poisoning?

Web cache poisoning, also known as DNS poisoning or DNS cache poisoning, is an internet-driven attack where the attacker exploits a web server vulnerability associated with caching the server. The attacker serves false information or malicious HTTP response, dragging the user's browsing to an incorrect or unsolicited web page. The impact of the manipulated response will depend on how or where the attacker wants to strike. Mostly, attackers target shared web caches, such as in proxy servers, to impact mass users. 

Such an attack usually redirects users to illegitimate or malicious sites from which malware or browser-hijacking program is downloaded automatically into user systems from rogue servers.

Web cache poisoning attacks often damage the company’s or brand’s reputation. It becomes challenging to verify the data stored in the corrupted caches. It means that the incorrect information resides in that cache until the time to live (TTL) value expires or security professionals resolve this issue manually.

How does web cache poisoning occur?

Once the attacker gains access to the DNS server, the attacker will input the fraudulent IP address or malicious server information. It will compel the DNS resolver to redirect to the malicious site. Attackers can successfully poison the web cache if the DNS is meant for smaller internet users and does not have proper security measures. Attackers can hijack the DNS cache and change its original data with hostile ones. 

Attackers often perform web cache poisoning to increase another website’s traffic, download malware in the victim’s system, generate vicious responses, damage the regular business workflow, or harm the brand’s reputation. Other than malware infection, data integrity, hampering security updates, and misleading users are popular motives for cache poisoning.

Preventative measures

1. Enterprises should use DNS Security Extensions (DNSSEC) protocol. It signs security policy at various DNS lookup levels, preventing poisoning of the DNS cache.

2. Various DNS spoof detection tools exist in the market. It confirms whether the DNS responses are legitimate.

3. Implementing end-to-end encryption is another technique to keep adversaries at bay from putting illegitimate information into the cache.

4. Enterprises can follow certain best practices like leveraging Virtual private network (VPN) applications and flushing our DNS cache to resolve cache poisoning.

5. Enterprises can also hire penetration testers, vulnerability detection teams, or security experts like Packetlabs to identify flaws in systems like JavaScript injection, cross-site scripting (XSS), and open redirection that may lead to web cache poisoning.

Conclusion 

While proactive security measures and best practices can help protect your business from web cache poisoning attacks, enterprise security professionals should consider regular browser patching, scanning systems using anti-malware and regular penetration testing to strengthen your security posture.