CVE-2026-66913 in Lookyloo
Summary
by MITRE • 07/28/2026
Lookyloo did not enforce limits on the decompressed size of uploaded capture archives and compressed HAR files.
An attacker could submit a specially crafted ZIP, gzip, or zlib-compressed capture containing data that expands to a very large size during processing. Because the application decompressed this content directly in memory without first limiting the output size, processing the malicious capture could exhaust available memory, terminate a web or worker process, or make the Lookyloo instance unavailable.
The vulnerability affects both full Lookyloo capture archive imports and API submissions containing gzip-compressed HAR data. Repeated exploitation could cause a persistent denial-of-service condition until the affected processes or instance are restarted.
The patch introduces:
* A 1 GB cumulative uncompressed-size limit for imported capture archives. * Size-limited gzip and zlib decompression for compressed HAR files. * Explicit detection and handling of suspected zip bombs. * An HTTP 400 response when an oversized compressed HAR file is submitted through the API.
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Analysis
by VulDB Data Team • 07/28/2026
This vulnerability in Lookyloo represents a critical denial-of-service weakness that stems from inadequate input validation and resource management during decompression operations. The flaw allows attackers to craft maliciously compressed files that expand significantly beyond their original size, creating a scenario where memory exhaustion occurs during processing. The vulnerability specifically affects the application's handling of ZIP, gzip, and zlib-compressed content, which are commonly used formats for web capture data and HAR files. According to CWE-400, this manifests as an insufficient resource pool size limitation, while the ATT&CK framework would categorize this under privilege escalation through resource exhaustion techniques. The root cause lies in the application's failure to implement proper decompression limits, allowing direct memory allocation without checking against predetermined thresholds.
The technical implementation of this vulnerability exploits the fundamental nature of compression algorithms where a small input file can expand to enormous sizes when decompressed. When Lookyloo processes these compressed files, it loads the decompressed content directly into memory without first validating or limiting the potential output size. This creates an ideal environment for zip bomb attacks, where attackers craft archives containing highly compressed data that expands to gigabytes of uncompressed content. The vulnerability impacts both the web interface and API endpoints, making it accessible through multiple attack vectors. When processing such malicious files, the application's memory consumption spikes dramatically, leading to process termination or complete service unavailability. This type of attack specifically aligns with CVE-2021-44228-style vulnerabilities where resource exhaustion leads to system instability.
The operational impact of this vulnerability extends beyond simple service disruption to potentially compromising the availability and reliability of Lookyloo instances. Repeated exploitation can maintain persistent denial-of-service conditions that require manual intervention through process restarts or complete system rebooting. The cumulative effect means that even legitimate users may experience degraded performance or complete service interruption during ongoing attacks. Organizations relying on Lookyloo for web capture analysis face significant risk of operational downtime, particularly in environments where continuous monitoring is required. The vulnerability affects both full capture archive imports and API submissions, making it a comprehensive threat across all data ingestion pathways.
The patch implementation addresses this vulnerability through multiple defensive layers that align with established security best practices. The introduction of a 1 gigabyte cumulative uncompressed-size limit for capture archives provides a hard boundary against excessive memory consumption while allowing normal operation to continue. Size-limited decompression for gzip and zlib files ensures that even individual compressed components cannot cause memory exhaustion. Explicit detection and handling of suspected zip bombs adds an additional layer of protection by identifying potentially malicious compression patterns before they can cause damage. The HTTP 400 response code for oversized compressed HAR files through the API provides clear feedback to attackers while preventing resource consumption on legitimate requests. These mitigations collectively address the CWE-400 category of insufficient resource pool size and provide defense-in-depth measures that protect against both known and unknown variants of compression-based attacks.