Opera 5.11 allows remote attackers to cause a denial of service (CPU consumption and memory leak) via a web page with a large number of images.
Opera 5.11 is vulnerable to a denial-of-service (DoS) attack that can be triggered remotely. By loading a webpage containing a large number of images, attackers can exhaust the browser's resources, leading to significant CPU consumption and a memory leak, effectively rendering the browser unusable. This vulnerability poses a risk of disrupting user access and potentially impacting business operations.
Step 1: Payload Delivery: The attacker crafts a malicious webpage containing a large number of image tags (e.g., <img> tags). These images can be real or dummy images, as the vulnerability lies in the processing of the tags themselves, not the images' content.
Step 2: User Interaction: The victim, using Opera 5.11, navigates to the malicious webpage, either directly or indirectly (e.g., via a link in an email or a compromised website).
Step 3: Image Loading Trigger: The Opera browser begins to parse the HTML and encounters the numerous <img> tags. It initiates a request to load each image.
Step 4: Resource Exhaustion: The browser's image loading engine, due to the vulnerability, enters an inefficient processing state. It consumes excessive CPU resources and leaks memory as it attempts to handle the large number of image requests.
Step 5: Denial of Service: The CPU usage spikes to 100%, and the memory consumption grows rapidly. The browser becomes unresponsive, and the user is unable to interact with it. This constitutes a denial-of-service condition.
The vulnerability stems from Opera 5.11's inefficient handling of image loading, specifically when dealing with a large quantity of images on a single webpage. The browser's image processing routines appear to lack proper resource management and error handling. The root cause is likely an unbounded loop or inefficient algorithm within the image loading and rendering engine. When faced with numerous image requests, the browser consumes excessive CPU cycles and allocates memory without proper deallocation, leading to a memory leak and ultimately a denial of service. The lack of throttling or rate limiting on image loading exacerbates the issue.