CVE-2026-114629 in Web::Simple
Summary
by MITRE • 10/24/2026
Web::Simple versions before 0.035 for Perl allocate a buffer sized by the Content-Length header for urlencoded body parameters.
Web::Dispatch::ParamParser::get_unpacked_body_from reads an application/x-www-form-urlencoded body using a single read call, with no cap and the return value ignored. Perl's read grows the buffer to the requested length before reading, so the declared Content-Length determines the allocation.
An attacker can trigger this through any route whose dispatch specification has a % body-parameter match, such as sub (POST + %name=), sending a Content-Length far larger than the body actually sent. No authentication is involved.
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Analysis
by VulDB Data Team • 10/24/2026
The vulnerability identified in Web::Simple versions prior to 0.035 represents a critical server-side resource exhaustion flaw rooted in improper input validation and unsafe memory allocation practices within the Perl web framework's request parsing logic. Specifically, the issue resides in the Web::Dispatch::ParamParser module, which is responsible for processing application/x-www-form-urlencoded body parameters during HTTP POST requests. The core technical defect occurs when the get_unpacked_body_from function attempts to read the incoming request body. Instead of implementing a safe buffer size limit or validating that the actual data received matches the declared length, the code relies directly on the Content-Length header provided by the client to determine the allocation size for an internal buffer. This design choice creates a direct dependency on untrusted input from the network layer without any sanitization or bounds checking mechanisms in place.
From a technical perspective, Perl's read function behaves dynamically when handling large data streams; it expands the target buffer to accommodate the requested length before attempting to perform the I/O operation. Consequently, if an attacker crafts a malicious HTTP POST request with a significantly inflated Content-Length header that far exceeds the actual size of the body payload being transmitted, the server will attempt to allocate memory corresponding to this exaggerated value. This behavior effectively bypasses standard network-level protections and application-layer limits because the allocation happens in user-space memory managed by the Perl interpreter rather than through constrained system calls with predefined caps. The return value of the read operation is ignored, meaning that even if the connection closes prematurely or only a fraction of the data arrives, the buffer remains allocated at its maximum requested size, leading to immediate and uncontrolled memory consumption on the server side.
The operational impact of this vulnerability is severe, primarily manifesting as a Denial of Service (DoS) condition against the web application infrastructure. Since no authentication is required to exploit this flaw, any anonymous attacker can trigger the resource exhaustion by sending specially crafted requests to routes that utilize body parameter matching, such as those defined with dispatch specifications like POST combined with %name= patterns. As multiple concurrent attacks are launched or even a single sustained attack from a determined adversary, the server's memory usage will spike rapidly until it hits system limits. This results in process crashes, service unavailability for legitimate users, and potential instability of the underlying host operating system if swap space is exhausted. The lack of authentication lowers the barrier to entry significantly, making this vulnerability attractive for automated scanning tools and opportunistic attackers seeking to disrupt services with minimal effort or cost.
This flaw aligns closely with CWE-400, which describes Uncontrolled Resource Consumption, as well as CWE-787, Out-of-bounds Write, due to the potential for memory corruption if the allocation fails or behaves unexpectedly under extreme pressure. In terms of offensive security frameworks, this vulnerability maps to MITRE ATT&CK technique T1496, Host Resource Hijacking: Denial of Service, where attackers leverage application logic flaws to consume excessive resources and degrade service availability. The exploitation vector is classified as Network Access with Low Complexity, indicating that the attack can be performed remotely over standard HTTP/HTTPS protocols without requiring prior access or complex setup procedures beyond crafting a specific HTTP header value.
To mitigate this vulnerability, organizations running Web::Simple versions before 0.035 must upgrade to version 0.035 or later immediately, as these newer releases include patches that enforce proper buffer size limits and validate input lengths against actual data received. For environments where immediate patching is not feasible due to dependency constraints, temporary mitigations should be implemented at the network perimeter using Web Application Firewalls (WAFs) or reverse proxies such as Nginx or Apache. These intermediary layers can be configured to enforce strict maximum body size limits and validate that the Content-Length header does not exceed a predefined threshold relative to actual payload sizes. Additionally, implementing rate limiting on POST endpoints can help mitigate the impact of volumetric attacks by throttling requests from single sources before they consume excessive server resources. Regular security audits focusing on input validation practices in web frameworks are also recommended to prevent similar resource exhaustion flaws in other components of the application stack.