CAPEC-275 Detail

An adversary serves content whose IP address is resolved by a DNS server that the adversary controls. After initial contact by a web browser (or similar client), the adversary changes the IP address to which its name resolves, to an address within the target organization that is not publicly accessible. This allows the web browser to examine this internal address on behalf of the adversary.

Execution Flow

[Identify potential DNS rebinding targets] An adversary publishes content on their own server with their own name and DNS server. Attract HTTP traffic and explore rebinding vulnerabilities in browsers, flash players of old version.

• Adversary uses Web advertisements to attract the victim to access adversary's DNS. Explore the versions of web browser or flash players in HTTP request.

[Establish initial target access to adversary DNS] The first time the target accesses the adversary's content, the adversary's name must be resolved to an IP address. The adversary's DNS server performs this resolution, providing a short Time-To-Live (TTL) in order to prevent the target from caching the value.

[Rebind DNS resolution to target address] The target makes a subsequent request to the adversary's content and the adversary's DNS server must again be queried, but this time the DNS server returns an address internal to the target's organization that would not be accessible from an outside source.

[Determine exploitability of DNS rebinding access to target address] The adversary can then use scripts in the content the target retrieved from the adversary in the original message to exfiltrate data from the named internal addresses.

[Access & exfiltrate data within the victim's security zone] The adversary can then use scripts in the content the target retrieved from the adversary in the original message to exfiltrate data from the internal addresses. This allows adversaries to discover sensitive information about the internal network of an enterprise.

• Adversary attempts to use victim's browser as an HTTP proxy to other resources inside the target's security zone. This allows two IP addresses placed in the same security zone.
• Adversary tries to scan and access all internal hosts in victim's local network by sending multiple short-lived IP addresses.

Prerequisites

The target browser must access content server from the adversary controlled DNS name. Web advertisements are often used for this purpose. The target browser must honor the TTL value returned by the adversary and re-resolve the adversary's DNS name after initial contact.

Skills Required

Setup DNS server and the adversary's web server. Write a malicious script to allow the victim to connect to the web server.

Resources Required

The adversary must serve some web content that a victim accesses initially. This content must include executable content that queries the adversary's DNS name (to provide the second DNS resolution) and then performs the follow-on attack against the internal system. The adversary also requires a customized DNS server that serves an IP address for their registered DNS name, but which resolves subsequent requests by a single client to addresses internal to that client's network.

Mitigations

Design: IP Pinning causes browsers to record the IP address to which a given name resolves and continue using this address regardless of the TTL set in the DNS response. Unfortunately, this is incompatible with the design of some legitimate sites.
Implementation: Reject HTTP request with a malicious Host header.
Implementation: Employ DNS resolvers that prevent external names from resolving to internal addresses.

Related Weaknesses

References

REF-119

Protecting Browsers from DNS Rebinding Attacks
Collin Jackson, Adam Barth, Andrew Bortz, Weidong Shao, Dan Boneh.

REF-120

Wikipedia
http://en.wikipedia.org/wiki/DNS_rebinding

Submission

Modifications