CVE-2008-2785 in Firefox
Summary
by MITRE
Mozilla Firefox before 2.0.0.16 and 3.x before 3.0.1, Thunderbird before 2.0.0.16, and SeaMonkey before 1.1.11 use an incorrect integer data type as a CSS object reference counter in the CSSValue array (aka nsCSSValue:Array) data structure, which allows remote attackers to execute arbitrary code via a large number of references to a common CSS object, leading to a counter overflow and a free of in-use memory, aka ZDI-CAN-349.
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Analysis
by VulDB Data Team • 09/05/2019
This vulnerability represents a critical memory corruption issue affecting multiple Mozilla-based applications including Firefox, Thunderbird, and SeaMonkey. The flaw resides in the CSSValue array data structure where an incorrect integer data type is used as a reference counter for CSS objects. This improper implementation creates a scenario where the reference counter can overflow when handling a large number of references to the same CSS object, ultimately leading to a use-after-free condition that adversaries can exploit for arbitrary code execution. The vulnerability was identified as ZDI-CAN-349 and demonstrates a classic buffer overflow scenario where integer arithmetic fails to properly handle reference counting operations. The affected versions span across the 2.0.0.16 and 3.0.1 release boundaries for their respective major versions, indicating this was a widespread issue affecting a significant portion of the user base during that period.
The technical implementation of this vulnerability involves the manipulation of CSS object reference counting mechanisms within the browser's rendering engine. When a large number of references are made to a common CSS object, the integer counter used for tracking these references eventually overflows beyond its maximum value, causing the system to incorrectly believe that the object is no longer in use. This misidentification triggers a premature memory deallocation, creating a dangling pointer that attackers can subsequently exploit to execute malicious code. The flaw specifically targets the nsCSSValue:Array data structure, which serves as a fundamental component in how CSS values are managed and stored during page rendering operations. The integer overflow occurs because the reference counter does not properly validate against maximum integer limits, allowing attackers to craft specific CSS content that forces the counter to wrap around and cause memory corruption.
From an operational perspective, this vulnerability presents a severe threat to user security as it allows remote code execution without requiring any user interaction beyond visiting a malicious webpage. Attackers can construct specially crafted web pages containing excessive CSS references that trigger the integer overflow condition, enabling them to execute arbitrary code with the privileges of the browser process. This represents a high-severity exploit that can be delivered through various attack vectors including phishing emails, compromised websites, or malicious advertisements. The vulnerability's impact extends beyond simple code execution as it can potentially lead to full system compromise, especially when combined with other exploitation techniques. The fact that this issue affected multiple Mozilla products simultaneously indicates a fundamental flaw in the underlying CSS processing architecture that required coordinated patches across different software components.
The vulnerability aligns with several common attack patterns documented in the attack mitigation framework, particularly those involving memory corruption and use-after-free conditions. It demonstrates characteristics consistent with CWE-190, Integer Overflow or Wraparound, where integer arithmetic operations fail to properly handle boundary conditions. Additionally, the exploitation technique corresponds to CWE-476, NULL Pointer Dereference, as the overflow leads to invalid memory access patterns. Security researchers have classified this vulnerability under attack techniques that leverage browser rendering engine flaws, placing it within the ATT&CK framework's T1203 category related to Exploitation for Client Execution. Organizations affected by this vulnerability should prioritize immediate patch deployment and implement network-level protections to prevent exploitation attempts. The incident highlights the importance of proper integer validation in memory management systems and underscores the critical need for thorough testing of reference counting mechanisms in complex software architectures.