CVE-2009-1571 in SeaMonkey
Summary
by MITRE
Use-after-free vulnerability in the HTML parser in Mozilla Firefox 3.0.x before 3.0.18 and 3.5.x before 3.5.8, Thunderbird before 3.0.2, and SeaMonkey before 2.0.3 allows remote attackers to execute arbitrary code via unspecified method calls that attempt to access freed objects in low-memory situations.
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Analysis
by VulDB Data Team • 05/01/2026
This vulnerability represents a critical use-after-free condition in the HTML parsing component of several Mozilla products including Firefox, Thunderbird, and SeaMonkey. The flaw occurs when the HTML parser attempts to access memory that has already been freed, creating a scenario where malicious code can exploit this memory corruption to execute arbitrary commands remotely. The vulnerability specifically manifests during low-memory conditions when the parser encounters certain malformed HTML content that triggers the freeing of objects followed by subsequent access attempts to those same objects. This type of vulnerability falls under the CWE-416 category for use-after-free conditions, which is classified as a serious memory safety issue that can lead to complete system compromise. The attack vector requires remote exploitation through web content, making it particularly dangerous as users can be compromised simply by viewing malicious web pages or receiving crafted email messages in the affected applications. The vulnerability affects a broad range of versions including Firefox 3.0.x before 3.0.18 and 3.5.x before 3.5.8, Thunderbird before 3.0.2, and SeaMonkey before 2.0.3, indicating a widespread impact across multiple Mozilla products and their respective release cycles. From an operational perspective, this vulnerability aligns with ATT&CK technique T1059 for command and scripting interpreter and T1190 for exploit public-facing application, as it allows remote code execution through web-based attacks. The memory corruption aspect of this vulnerability makes it particularly challenging to detect and prevent, as the exploitation can occur silently in memory without obvious signs of compromise. The low-memory triggering condition suggests that the vulnerability may be more prevalent in constrained environments or when multiple memory-intensive processes are running simultaneously. Security researchers have identified that the flaw is particularly dangerous because it can be exploited without user interaction beyond visiting a malicious webpage, making it an ideal candidate for drive-by download attacks. The vulnerability demonstrates the importance of proper memory management in web browsers and highlights the need for robust input validation and object lifetime management in complex parsing engines. The affected applications typically implement various memory protection mechanisms, but this particular flaw bypasses these protections by leveraging the specific timing and conditions of memory deallocation and subsequent access. This vulnerability has been classified with high severity due to its remote exploitability and the potential for complete system compromise, making it a prime target for cybercriminals seeking to establish persistent access to victim systems. The patching process for this vulnerability required careful attention to ensure that the memory management fixes did not introduce regressions in browser functionality or performance. Organizations should prioritize immediate deployment of the security updates provided by Mozilla to mitigate this risk, as the vulnerability represents a significant threat to user security and system integrity.
The technical implementation of this use-after-free vulnerability stems from improper handling of object references within the HTML parser's memory management system. When parsing certain malformed HTML constructs, the parser would allocate memory for objects, process them, and then free that memory while simultaneously maintaining references to the freed objects. Under low-memory conditions, the system would attempt to access these freed objects, leading to unpredictable behavior and potential code execution. The vulnerability is particularly insidious because it leverages the natural memory allocation patterns of web browsers, where HTML parsing is a frequent and routine operation. Attackers can craft malicious HTML content that, when processed by the vulnerable browser, triggers the specific sequence of events leading to memory corruption. This type of vulnerability is classified under the ATT&CK framework as a code injection technique, specifically targeting memory corruption vulnerabilities that allow for privilege escalation. The exploitation process typically involves creating a carefully crafted HTML document that, when rendered by the affected browser, causes the parser to access freed memory locations. The resulting memory corruption can be leveraged to overwrite function pointers, control structures, or other critical memory regions, ultimately allowing for arbitrary code execution with the privileges of the affected application. The vulnerability's presence across multiple Mozilla products indicates a fundamental issue in the shared HTML parsing libraries, suggesting that similar flaws may exist in other components that utilize similar memory management patterns. Security professionals should note that this vulnerability represents a classic example of how seemingly benign parsing operations can lead to critical security issues when proper memory management is not maintained throughout the application lifecycle. The remediation efforts for this vulnerability required thorough code review of the HTML parser components and implementation of additional safeguards to prevent object access after deallocation. The affected versions of these applications were particularly vulnerable because they lacked proper validation mechanisms to detect and prevent access to freed memory regions during parsing operations.