CVE-2026-77166 in Collectives
Summary
by MITRE • 09/21/2026
The emoji field in the page emoji update endpoint does not properly validate user input. By injecting long text and line breaks, the sidebar layout becomes broken and can hide other items.
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Analysis
by VulDB Data Team • 09/21/2026
This vulnerability represents a classic case of insufficient input validation within a web application interface, specifically affecting the functionality responsible for updating custom emoji assets. The core technical flaw lies in the backend processing logic associated with the page emoji update endpoint, which fails to enforce strict constraints on the length and character composition of user-supplied data. Instead of sanitizing or truncating excessively long strings or stripping out control characters such as line breaks, the application accepts these inputs directly and renders them into the Document Object Model without adequate boundary checks. This lack of validation allows an attacker to inject payloads containing extended text sequences interspersed with newline characters that exceed the expected dimensions for a standard emoji label or icon container.
The operational impact of this flaw manifests as a layout disruption within the user interface, specifically targeting the sidebar navigation area. When the malformed input is rendered, the injected line breaks cause the element to expand vertically beyond its allocated space in the CSS grid or flexbox structure governing the sidebar. This expansion forces adjacent elements to shift position or become obscured by the oversized emoji entry. Consequently, other critical menu items or functional buttons within that sidebar can be hidden from view, effectively creating a Denial of Service condition for specific UI components. While this does not typically lead to direct code execution or data exfiltration on its own, it degrades the usability and integrity of the application interface, potentially preventing users from accessing necessary features or navigating the system correctly.
From a classification perspective, this vulnerability aligns with CWE-20 Improper Input Validation, as the software does not adequately verify that user input conforms to expected formats before processing. Furthermore, because the impact involves manipulating the visual presentation of the page through injected content rather than executing arbitrary scripts in most modern browsers due to Content Security Policies and HTML5 standards, it may also relate to CWE-79 Cross-site Scripting if the line breaks allow for breaking out of specific context boundaries that could lead to reflected or stored XSS. In terms of adversary tactics, this behavior is consistent with ATT&CK technique T1082 System Information Discovery, as an attacker might use such UI manipulation to map out available interface elements and identify hidden functionalities by observing how the layout shifts when different inputs are applied.
To mitigate this vulnerability, developers must implement rigorous input validation on both the client-side and server-side of the emoji update endpoint. On the frontend, JavaScript should enforce maximum length limits for text fields and strip or escape special characters like newlines before submission to prevent CSS injection-like effects that disrupt layout. More critically, the backend API must validate all incoming data against a strict schema, rejecting any payload where the emoji name exceeds a reasonable character limit, typically around twenty to thirty characters depending on design requirements. Additionally, implementing Content Security Policy headers can help mitigate potential secondary impacts by restricting how scripts and styles are rendered, although input sanitization remains the primary defense mechanism for this specific class of interface manipulation flaws.