Source: cve@mitre.org
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. A malicious webpage containing a large number of images 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 to users browsing untrusted websites, potentially disrupting their workflow or even crashing their systems.
Step 1: Payload Delivery: The attacker crafts a malicious HTML webpage. This webpage contains a large number of <img> tags, each referencing an image, either local or remote.
Step 2: User Interaction: The victim user navigates to the malicious webpage using Opera 5.11.
Step 3: Image Loading Trigger: Opera 5.11 begins to parse the HTML and attempts to load the images specified in the <img> tags.
Step 4: Resource Exhaustion: Due to the large number of images and the vulnerability in Opera's image handling, the browser's CPU usage spikes, and memory allocation increases rapidly.
Step 5: Denial of Service: The browser becomes unresponsive, and the system may become sluggish or crash due to the CPU consumption and memory leak. The user is unable to use the browser.
The vulnerability stems from Opera 5.11's inefficient handling of image loading within a webpage. Specifically, the browser fails to properly manage resources when faced with a large number of images. The root cause is likely an unoptimized image processing loop or a lack of proper resource limits. When the browser attempts to render a webpage with numerous images, it enters a state of high CPU utilization and memory allocation that it cannot efficiently release. This leads to a memory leak and excessive CPU usage, ultimately causing a DoS. The browser likely attempts to load and process each image without proper throttling or resource management, leading to the exhaustion of system resources. The lack of proper error handling or resource limits exacerbates the issue, allowing the process to consume all available resources.
Due to the age of the vulnerability and the affected software, it is unlikely to be associated with any specific APT groups or modern malware campaigns. It is not listed on the CISA KEV catalog.
High CPU utilization by the Opera process.
Excessive memory consumption by the Opera process.
Network traffic spikes when loading the malicious webpage (if images are remote).
Unusually long page load times for pages with many images.
System instability or unresponsiveness when browsing specific websites.
Upgrade to a modern, supported web browser (e.g., Chrome, Firefox, Edge).
If using Opera 5.11 is unavoidable (highly unlikely), restrict browsing to trusted websites only.
Implement a web application firewall (WAF) to filter malicious requests, although this is unlikely to be effective against a client-side DoS.
Monitor system resource usage (CPU, memory) to detect unusual activity.