CVE-2026-103087 in gosub-engine
Summary
by MITRE • 09/30/2026
Uncontrolled recursion in the Gosub browser engine (gosub-engine) through 0.1.0 and main before commit 46868b3 allows a remote attacker to cause a Denial of Service (stack exhaustion and application crash) via an SVG document containing an excessive number of deeply nested elements. Because the engine does not limit the nesting depth of processed SVG nodes, rendering such a document overflows the thread stack and terminates the application. The malicious SVG can be embedded through the SRC attribute of an IMG element, and thus exploitation only requires the victim to visit an attacker-controlled web page.
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Analysis
by VulDB Data Team • 09/30/2026
The vulnerability identified in the gosub-engine browser engine represents a critical uncontrolled recursion flaw that leads to stack exhaustion and subsequent application crash. This issue stems from the engine's failure to enforce limits on the nesting depth of SVG nodes during rendering processes. In standard software architecture, recursive operations or deep tree traversals require explicit safeguards such as maximum depth counters or iterative approaches with manual stack management to prevent resource depletion. The gosub-engine lacks these protective mechanisms for its SVG parsing logic, allowing an attacker to construct a maliciously crafted Scalable Vector Graphics document that contains an excessive number of deeply nested elements. When the engine attempts to render this structure, it initiates recursive function calls corresponding to each level of nesting without any termination condition based on depth. This behavior directly violates fundamental principles of robust input validation and resource management in web rendering engines.
From a technical perspective, the core flaw lies in how the parser handles hierarchical SVG structures. Each nested element triggers additional processing steps that consume stack space within the execution thread responsible for rendering. As the nesting depth increases linearly or exponentially depending on the document structure, the call stack grows until it exceeds the allocated memory limit for the thread. This results in a stack overflow exception, which typically causes immediate termination of the application process rather than graceful error handling. The absence of bounds checking means that even moderately complex SVG files can trigger this condition if they contain sufficient levels of parent-child relationships among elements such as groups, paths, or shapes. This design oversight highlights a significant gap in defensive coding practices where recursive algorithms are employed without corresponding depth constraints.
The operational impact of this vulnerability is severe denial of service against users interacting with the gosub-engine browser. Since exploitation requires only that the victim visits an attacker-controlled web page containing the malicious SVG embedded via the SRC attribute of an IMG element, the attack vector is highly accessible and easy to deploy at scale. There are no prerequisites for user interaction beyond initial page load, making this a remote code execution equivalent in terms of ease of use though limited strictly to denial of service effects due to stack exhaustion rather than arbitrary memory corruption. The resulting crash disrupts normal browsing activities and can lead to data loss if unsaved work is present within the browser session. Furthermore repeated exploitation attempts could be used as part of larger campaigns targeting system stability or availability metrics for services relying on this engine.
This vulnerability aligns with CWE-675 which describes operations that are not limited by maximum recursion depth, leading to resource exhaustion. It also maps closely to MITRE ATT&CK technique T1499 Endpoint Denial of Service where attackers leverage software vulnerabilities to disrupt availability rather than compromise confidentiality or integrity. The specific mechanism involves abusing legitimate rendering functionality through crafted input data structures that exploit internal algorithmic assumptions about safe processing limits. Mitigation strategies must focus on implementing explicit depth counters within the SVG parser logic to reject documents exceeding predefined thresholds before full recursive traversal occurs. Additionally adopting iterative parsing methods where possible can reduce reliance on deep call stacks altogether. Security testing should include fuzzing of SVG inputs with varying levels of nesting complexity to verify that proper bounds checking is enforced across all rendering paths.