CVE-1999-1283 is a vulnerability found in Opera Web Browser version 3.2.1, an early version of the Opera browser. The flaw allows remote attackers to cause a denial of service (DoS) by crashing the application. This is achieved by crafting a malicious URL containing an extra forward slash ('/') within the 'http://' scheme portion of the URL. When the vulnerable Opera 3.2.1 browser processes such a malformed URL, it triggers an application crash, resulting in a denial of service condition. The vulnerability does not affect confidentiality or integrity, nor does it require authentication or user interaction beyond visiting or processing the malicious URL. The CVSS score assigned is 5.0 (medium severity), reflecting the ease of remote exploitation without authentication but limited impact scope to availability only. No patch is available for this vulnerability, and there are no known exploits in the wild. Given the age of the vulnerability (published in 1998) and the obsolete nature of Opera 3.2.1, modern systems are unlikely to be affected. However, legacy systems or environments still running this outdated browser version remain susceptible to this DoS attack.

For European organizations, the direct impact of this vulnerability is limited due to the obsolescence of Opera 3.2.1. Most organizations have long since migrated to modern browsers with robust security updates. However, if any legacy systems or specialized environments still use Opera 3.2.1—such as in industrial control systems, embedded devices, or archival setups—these could be vulnerable to remote denial of service attacks. An attacker could disrupt business operations by causing browser crashes, potentially affecting user productivity or automated processes relying on this browser. The impact is confined to availability, with no risk to data confidentiality or integrity. Given the low prevalence of this browser version, the overall risk to European organizations is minimal but should not be ignored in legacy contexts.

Since no patch is available for Opera 3.2.1, the primary mitigation is to upgrade to a modern, supported browser version that addresses this and other vulnerabilities. Organizations should conduct an inventory of software assets to identify any legacy systems running Opera 3.2.1 and plan their upgrade or decommissioning. Network-level mitigations include filtering or blocking suspicious URLs containing malformed 'http://' schemes to prevent triggering the vulnerability. Additionally, implementing web proxy solutions that sanitize or validate URLs before they reach client browsers can reduce exposure. For environments where upgrading is not immediately feasible, isolating affected systems from untrusted networks and restricting access to trusted users can minimize risk.