CVE-2006-5633 in Seamonkey
Summary
by MITRE
Firefox 1.5.0.7 and 2.0, and Seamonkey 1.1b, allows remote attackers to cause a denial of service (crash) by creating a range object using createRange, calling selectNode on a DocType node (DOCUMENT_TYPE_NODE), then calling createContextualFragment on the range, which triggers a null dereference. NOTE: the original Bugtraq post mentioned that code execution was possible, but followup analysis has shown that it is only a null dereference.
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Analysis
by VulDB Data Team • 04/26/2026
This vulnerability affects Mozilla Firefox versions 1.5.0.7 and 2.0, as well as SeaMonkey version 1.1b, representing a denial of service condition that can be exploited remotely by malicious actors. The flaw resides in the browser's handling of DOM (Document Object Model) range objects and their interaction with DocType nodes, specifically when the createRange method is used in conjunction with selectNode targeting DOCUMENT_TYPE_NODE elements. The vulnerability manifests when a range object is created, a DocType node is selected, and then createContextualFragment is invoked on that range, resulting in a null pointer dereference that causes the browser to crash.
The technical implementation of this vulnerability follows a specific sequence of DOM operations that exposes a memory management flaw in the browser's rendering engine. When the selectNode method is called on a range object with a DocType node as its argument, the internal data structures become corrupted or improperly initialized. Subsequent calls to createContextualFragment on this malformed range object trigger a null dereference condition where the application attempts to access memory at a null pointer address. This type of vulnerability falls under CWE-476, which specifically addresses NULL Pointer Dereference, and represents a classic example of improper handling of edge cases in DOM manipulation operations.
The operational impact of this vulnerability extends beyond simple browser crashes, as it can be leveraged by attackers to disrupt user sessions and potentially degrade service availability. While the original reports suggested code execution capabilities, subsequent analysis has confirmed that this is strictly a denial of service vulnerability that results in browser instability rather than arbitrary code execution. However, the implications remain significant for web security, as users may be unable to access legitimate websites or may experience unexpected browser termination during normal browsing activities. This vulnerability aligns with ATT&CK technique T1499.004, which covers Network Denial of Service, as it can be used to create a persistent disruption of service for affected users.
Mitigation strategies for this vulnerability should focus on immediate patch application, as Mozilla released updates to address the specific DOM handling issue. Organizations should ensure their browser deployment policies include regular security updates and consider implementing browser hardening measures such as disabling unnecessary DOM manipulation features when possible. The vulnerability highlights the importance of proper input validation and memory management in web browser implementations, particularly when dealing with edge cases involving different node types in the document structure. Additionally, web application firewalls and intrusion detection systems can be configured to monitor for suspicious DOM manipulation patterns, though the primary defense remains keeping browser software current with security patches.