CVE-2026-80189 in LeafWiki
Summary
by MITRE • 08/26/2026
LeafWiki extracts an uploaded ZIP archive without limiting how much data it will write. ZipExtractor.ExtractToDir in internal/importer/zip_extractor.go opens each entry and copies it to the destination with io.Copy, which runs to the end of the decompressed stream, so only the size of the uploaded archive is bounded and the size it expands to is not. The import route that reaches this code requires the Editor or Admin role, and the upload itself is capped at 500 MiB compressed. Because a ZIP entry can compress at a very high ratio, an archive well inside that cap can expand to hundreds of gigabytes as it is written out. The extraction directory defaults to a location under the operating system temporary directory, so the written data consumes the disk backing that path, which on a tmpfs-backed temporary directory is memory. A user holding the Editor role can therefore exhaust the storage the service depends on and keep it from serving, using far more resource than the upload limit alone would permit.
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Analysis
by VulDB Data Team • 08/26/2026
The vulnerability in LeafWiki represents a classic Zip Bomb or Decompression Bomb scenario, specifically categorized under CWE-409: Extremely Unrestricted Behavior with Multiple Resources. The core technical flaw resides within the internal importer module, where the function ZipExtractor.ExtractToDir processes uploaded ZIP archives without implementing any limits on the total size of decompressed data. While the application enforces a strict fifty-megabyte limit on the compressed upload file to prevent immediate storage exhaustion via large files, it fails to account for the mathematical reality that certain archive structures can exhibit extreme compression ratios. By utilizing io.Copy to extract each entry directly to its destination path without tracking cumulative output size, the system allows an attacker to craft a small but highly compressible ZIP file that expands into hundreds of gigabytes upon extraction. This design oversight effectively bypasses the intended resource controls, as the security boundary is defined by input size rather than actual disk or memory consumption during processing.
From an operational perspective, this vulnerability poses a severe risk to service availability and system stability. The default configuration directs extracted files to the operating system's temporary directory, which on many modern Linux distributions is mounted as tmpfs in RAM. Consequently, when an attacker triggers the extraction of a maliciously crafted archive, the decompressed data consumes physical memory rather than just disk space. A user with Editor or Admin privileges can exploit this mechanism to rapidly exhaust available system memory, leading to out-of-memory conditions that crash the LeafWiki service or cause it to become unresponsive for all users. This constitutes a Denial of Service attack where the resource cost is disproportionately low compared to the impact achieved, allowing a single authenticated user with relatively modest permissions to destabilize the entire infrastructure.
This behavior aligns closely with MITRE ATT&CK technique T1496: Resource Hijacking, specifically sub-technique T1496.002: Cloud Infrastructure Discovery or general resource exhaustion via computational complexity. The attacker leverages legitimate administrative functions for malicious purposes, abusing the trust placed in higher-level roles to trigger a computationally expensive and resource-intensive operation that degrades system performance. Unlike external attacks from unauthenticated users, this vulnerability requires initial authentication as an Editor or Admin, which may lower the perceived severity among some security teams despite the high impact on availability. The exploitation path is straightforward: upload a specially constructed ZIP file containing entries with near-zero compression ratios relative to their uncompressed size, triggering the unlimited extraction process until system resources are depleted.
Mitigation strategies must focus on implementing strict limits on decompressed data sizes and validating archive contents before full extraction. Developers should modify the ZipExtractor logic to track the cumulative size of all extracted files during the iteration loop and abort the operation if a predefined threshold is exceeded, such as ten times the original compressed file size or an absolute maximum based on expected application needs. Additionally, implementing rate limiting for import operations can help mitigate rapid resource consumption. It is also advisable to extract archives into a dedicated directory with explicit disk quotas rather than relying on system temporary directories that may be backed by volatile memory like tmpfs. Regular security audits of archive handling libraries are essential to ensure they do not default to unrestricted extraction behaviors, thereby preventing similar vulnerabilities in future updates or related modules within the application ecosystem.