CVE-2026-50787 in E-Sic Livre
Summary
by MITRE • 10/23/2026
e-SIC Livre (esiclivre) v0.2.2 and earlier contains an uncontrolled resource consumption vulnerability in restrito/inc/captcha.php. The application uses user-supplied parameters (l, a, tf, ql) without validation to generate CAPTCHA images, allowing remote attackers to cause denial of service via excessive memory and CPU consumption.
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Analysis
by VulDB Data Team • 10/23/2026
The e-SIC Livre software version 0.2.2 and earlier contains a critical uncontrolled resource consumption vulnerability located within the restrito/inc/captcha.php module. This flaw stems from an insufficient validation mechanism for user-supplied input parameters, specifically l, a, tf, and ql. These parameters are directly utilized in the generation process of CAPTCHA images without any bounds checking or sanitization. In typical web application architectures, CAPTCHA systems are designed to generate small graphical challenges that require minimal computational resources. However, because this implementation fails to constrain the input values, an attacker can manipulate these parameters to trigger disproportionately large image rendering operations. This lack of input validation allows for a direct exploitation path where malicious actors can force the server to allocate excessive amounts of memory and CPU cycles during the CAPTCHA generation process.
From a technical perspective, this vulnerability is classified under CWE-400, which covers uncontrolled resource consumption. The core issue lies in the application's failure to implement rate limiting or input size constraints before invoking image processing libraries. When an attacker supplies extreme values for parameters such as ql (likely related to query length or quantity) or tf (possibly time factor or text field), the underlying graphics library may attempt to render images of massive dimensions or with excessive complexity. This results in a denial of service condition where legitimate users are unable to access the application because server resources are exhausted by these malicious requests. The vulnerability is particularly dangerous as it can be exploited remotely without authentication, allowing any internet user to contribute to the degradation of system performance.
The operational impact of this flaw extends beyond simple resource exhaustion. By continuously sending crafted requests that trigger high CPU and memory usage, an attacker can effectively take down the web server or cause significant latency for all users interacting with the e-SIC Livre platform. This aligns with MITRE ATT&CK technique T1496, which describes Resource Hijacking where attackers use compromised resources to perform computationally intensive tasks or simply degrade service availability. In a government context such as that served by e-SIC (Electronic Access to Information Law), maintaining high availability is crucial for public trust and operational continuity. A successful denial of service attack could prevent citizens from submitting requests, accessing documents, or interacting with essential civic services, thereby undermining the primary function of the application.
To mitigate this vulnerability, immediate remediation steps should focus on implementing strict input validation and resource limits within the captcha.php module. Developers must enforce maximum allowable values for parameters l, a, tf, and ql to ensure that generated images remain within reasonable size and complexity thresholds. Additionally, integrating rate limiting mechanisms at both the application layer and network perimeter can help detect and block abnormal request patterns indicative of such attacks. It is also advisable to employ CAPTCHA solutions that are less susceptible to resource exhaustion by using lightweight verification methods or third-party services with built-in protection against abuse. Regular security audits and code reviews should be conducted to identify similar uncontrolled resource consumption flaws in other parts of the application, ensuring a more robust defense posture against denial of service attacks.