CVE-2004-1617 in Lynx
Summary
by MITRE
Lynx, lynx-ssl, and lynx-cur before 2.8.6dev.8 allow remote attackers to cause a denial of service (infinite loop) via a web page or HTML email that contains invalid HTML including (1) a TEXTAREA tag with a large COLS value and (2) a large tag name in an element that is not terminated, as demonstrated by mangleme. NOTE: a followup suggests that the relevant trigger for this issue is the large COLS value.
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Analysis
by VulDB Data Team • 06/30/2021
The vulnerability identified as CVE-2004-1617 affects the Lynx web browser and its related components including lynx-ssl and lynx-cur versions prior to 2.8.6dev.8. This security flaw represents a classic denial of service condition that can be exploited remotely by malicious actors to disrupt service availability for legitimate users. The vulnerability specifically targets the HTML parsing mechanism within these browser implementations, creating a scenario where valid user input can trigger unexpected behavior leading to system instability.
The technical implementation of this vulnerability stems from inadequate input validation and parsing logic within the Lynx browser's HTML processor. When processing web pages or HTML email content containing malformed HTML structures, the browser encounters a specific combination of elements that causes it to enter an infinite loop during parsing operations. The primary trigger involves a TEXTAREA tag with an excessively large COLS attribute value, combined with another element containing an oversized tag name that remains improperly terminated. This particular sequence of malformed HTML elements creates a parsing scenario where the browser's internal state management becomes corrupted, leading to continuous processing loops that consume system resources without resolution.
The operational impact of this vulnerability extends beyond simple service disruption to potentially affect system availability and resource consumption. Attackers can exploit this weakness by crafting malicious web pages or email content that, when processed by vulnerable Lynx installations, causes the browser to become unresponsive or consume excessive CPU cycles. The infinite loop condition can persist until the system resources are exhausted or manual intervention is required to terminate the affected process. This makes the vulnerability particularly dangerous in environments where automated browsing or email processing is common, as it could lead to cascading failures affecting multiple users or systems.
From a cybersecurity perspective, this vulnerability aligns with CWE-835, which addresses the issue of infinite loops in software implementations. The flaw demonstrates poor input validation practices that allow malformed data to propagate through the parsing pipeline without proper bounds checking. The ATT&CK framework categorizes this as a Denial of Service technique under the T1499 category, specifically targeting application availability through resource exhaustion. The vulnerability also reflects broader concerns about HTML parser robustness and the importance of implementing proper input sanitization mechanisms to prevent exploitation of parsing vulnerabilities.
Mitigation strategies for CVE-2004-1617 require immediate software updates to versions 2.8.6dev.8 or later where the parsing logic has been corrected to handle large COLS values and malformed HTML elements appropriately. Organizations should also implement additional defensive measures such as HTML content filtering at network boundaries, email scanning solutions that can detect and block malicious HTML content, and regular security assessments of browser installations. Network administrators should consider implementing rate limiting and resource monitoring to detect unusual CPU consumption patterns that might indicate exploitation attempts. The fix typically involves enhancing the HTML parser to include proper bounds checking and termination conditions for parsing operations, ensuring that malformed input does not cause the browser to enter infinite loops during processing operations.