CVE-2010-0220 in Firefox
Summary
by MITRE
The nsObserverList::FillObserverArray function in xpcom/ds/nsObserverList.cpp in Mozilla Firefox before 3.5.7 allows remote attackers to cause a denial of service (application crash) via a crafted web site that triggers memory consumption and an accompanying Low Memory alert dialog, and also triggers attempted removal of an observer from an empty observers array.
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Analysis
by VulDB Data Team • 08/30/2021
The vulnerability identified as CVE-2010-0220 resides within the nsObserverList::FillObserverArray function in Mozilla Firefox's xpcom/ds/nsObserverList.cpp component, representing a critical denial of service weakness that affected versions prior to 3.5.7. This flaw operates through a sophisticated exploitation mechanism that leverages the browser's observer pattern implementation, where multiple components can register for notifications about specific events within the application lifecycle. The vulnerability specifically targets the internal observer list management system that handles notification dispatching for various browser events, creating a scenario where malicious web content can manipulate the observer registration and removal processes in unexpected ways.
The technical exploitation of this vulnerability occurs when a remote attacker crafts a malicious website that triggers the FillObserverArray function with malformed observer data, leading to a cascade of memory allocation operations that consume excessive system resources. The flaw manifests when the application attempts to remove an observer from what it perceives as an empty observers array, but due to improper bounds checking and array management, the system encounters a memory corruption scenario. This results in the application crashing with a Low Memory alert dialog, effectively causing a denial of service condition that prevents normal browser operation. The vulnerability operates under CWE-125, which addresses out-of-bounds read conditions, and specifically relates to improper handling of array indices and memory management within the observer pattern implementation.
The operational impact of this vulnerability extends beyond simple application instability, as it provides attackers with a reliable method to disrupt user browsing sessions and potentially interfere with browser functionality during critical operations. When exploited, the vulnerability can cause Firefox to become unresponsive or crash entirely, requiring users to manually restart the browser application. This type of denial of service attack can be particularly problematic in environments where browser stability is crucial for business operations or user productivity. The vulnerability also demonstrates a weakness in the browser's memory management and error handling protocols, as the system should have properly validated observer array states before attempting removal operations.
Mitigation strategies for CVE-2010-0220 primarily involve immediate patching of affected Firefox installations to version 3.5.7 or later, where the underlying observer list management has been corrected to properly validate array states and prevent memory corruption during observer removal operations. Security administrators should also implement browser hardening measures including disabling unnecessary JavaScript features, implementing content security policies, and monitoring for unusual memory consumption patterns that might indicate exploitation attempts. Organizations should consider deploying web application firewalls that can detect and block malicious patterns associated with this vulnerability, particularly those involving observer pattern manipulation and memory consumption attacks. The vulnerability serves as a reminder of the importance of proper input validation and memory management in complex software systems, aligning with ATT&CK technique T1499.004 for network denial of service and emphasizing the need for robust observer pattern implementations that properly handle edge cases and invalid states.