CVE-2026-58486 in HedgeDoc
Summary
by MITRE • 07/14/2026
HedgeDoc is an open source, real-time, collaborative, markdown notes application. Prior to version 1.11.0, HedgeDoc was vulnerable to a YAML alias bomb due to unsafe processing of the note frontmatter. HedgeDoc parsed frontmatter with js-yaml.load (js-yaml v3) via @hedgedoc/meta-marked, which resolved YAML anchor aliases. A compact malicious payload could therefore expand into a huge object structure, consuming excessive CPU. This expansion ran on every request to the publish view (/s/<shortid>) and, when placed under the opengraph key, the editor view (/<noteId>). A ten-level alias bomb could block the single Node.js event loop for roughly 235 seconds per request, causing concurrent requests to hang or drop and rendering the instance unavailable (DoS). Because the note was stored in the database, the impact survived process restarts until the note was removed. toobusy-js did not reliably mitigate the worst cases, as the event loop was saturated before the middleware could respond. This issue was fixed in version 1.11.0.
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Analysis
by VulDB Data Team • 07/14/2026
HedgeDoc represents a widely-used collaborative markdown editing platform that enables real-time document creation and sharing through web-based interfaces. The application's architecture relies heavily on frontmatter processing for note metadata management, which became a critical security weakness due to inadequate input validation mechanisms. This vulnerability specifically targeted the YAML parsing functionality within the application's core components, creating a pathway for malicious actors to exploit fundamental design flaws in the document processing pipeline. The issue manifested through the unsafe utilization of js-yaml.load function version 3, which processed note frontmatter through the @hedgedoc/meta-marked module without proper sanitization or resource limitation controls.
The technical flaw exploited a well-documented vulnerability pattern involving YAML alias resolution and object expansion that maps directly to CWE-400, specifically related to excessive resource consumption through uncontrolled data expansion. When maliciously crafted YAML content containing anchor aliases was processed, the js-yaml library would recursively resolve these aliases, creating exponentially expanding object structures that consumed disproportionate computational resources. The vulnerability enabled attackers to construct compact payloads that could expand into massive data structures, with a ten-level alias bomb capable of blocking the Node.js event loop for approximately 235 seconds per request. This particular implementation flaw demonstrated how YAML processing can become a vector for denial-of-service attacks when proper boundary controls are not implemented.
The operational impact of this vulnerability created cascading failures across the HedgeDoc application architecture, particularly affecting both publish and editor views where frontmatter processing occurred. When malicious content was placed within the opengraph key field, it triggered the vulnerable code path in both interfaces, creating multiple attack vectors for exploitation. The sustained event loop blocking prevented concurrent request handling, leading to complete service unavailability and potentially causing connection timeouts or dropped requests that disrupted user experience. The persistence of this vulnerability meant that once a malicious note was stored in the database, the DoS conditions would persist through application restarts until the compromised note was manually removed from storage. This characteristic made the vulnerability particularly dangerous as it could remain dormant until activated by specific request patterns, creating an insidious threat vector.
The mitigation strategy implemented in version 1.11.0 addressed this vulnerability through proper YAML parsing configuration changes that disabled unsafe alias resolution features within js-yaml. The fix aligns with ATT&CK technique T1498.001 related to resource exhaustion via malformed data processing, and specifically targets the exploitation patterns documented in CWE-770 for excessive resource consumption. Organizations deploying HedgeDoc should implement immediate patching strategies to address this vulnerability, as the attack surface includes both public publish endpoints and internal editor interfaces. Additional defensive measures include implementing request rate limiting mechanisms and proper input validation for all frontmatter processing components, ensuring that YAML parsing operations are bounded and monitored for abnormal resource consumption patterns.
This vulnerability exemplifies how seemingly innocuous data processing functions can become critical security weaknesses when combined with event-driven architectures and single-threaded execution models. The exploitation demonstrates the importance of implementing proper resource constraints and input sanitization in applications handling untrusted data, particularly when using libraries that support advanced features like YAML alias resolution. The incident highlights the need for comprehensive security testing that includes stress testing with malformed inputs to identify potential denial-of-service vectors before deployment in production environments where such vulnerabilities could compromise service availability and user experience.