CVE-2026-115825 in HTTP::Server::PSGI
Summary
by MITRE • 10/25/2026
HTTP::Server::PSGI versions before 1.0056 for Perl allow a single request to crash the server by declaring a large Content-Length.
The request body is read with sysread() calls sized by the remaining Content-Length. Perl grows the read buffer to the requested length before any data arrives, so the server tries to allocate as much memory as the client declares.
A remote attacker can send one request with a large Content-Length and a few body bytes, and perl exits with an out-of-memory error before the application is called. HTTP::Server::PSGI runs as a single process, so the server stays down until restarted.
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Analysis
by VulDB Data Team • 10/25/2026
The vulnerability identified in versions of HTTP::Server::PSGI prior to 1.0056 represents a critical resource exhaustion flaw rooted in improper input validation and memory allocation strategies within the Perl web server interface layer. This issue specifically targets the handling of HTTP request headers, particularly the Content-Length field which dictates the size of the message body expected by the server. In standard HTTP operations, this header is used to determine how much data should be read from the network socket before processing begins or passing control to the application logic. However, in vulnerable versions of HTTP::Server::PSGI, the implementation fails to validate whether the declared Content-Length value is reasonable relative to available system resources or predefined limits. Instead of implementing a safeguard against excessively large values, the server blindly trusts this client-supplied parameter and proceeds to allocate memory accordingly. This design flaw allows an unauthenticated remote attacker to exploit the mechanism by sending a single HTTP request with a significantly inflated Content-Length header while providing only minimal actual body data.
From a technical perspective, the core of the vulnerability lies in how Perl handles buffer allocation during input reading operations. When HTTP::Server::PSGI processes incoming requests, it utilizes sysread calls that are sized based on the remaining portion of the declared Content-Length. Crucially, before any substantial amount of data is actually received from the network, Perl attempts to pre-allocate a memory buffer large enough to hold the entirety of the claimed body size. This eager allocation strategy means that if an attacker specifies a Content-Length value in the gigabytes or even terabytes range, the server process will attempt to reserve that massive amount of contiguous virtual address space and physical RAM immediately upon receiving the header. Since this allocation occurs before any meaningful data transfer takes place, it does not require sustained bandwidth from the attacker but rather just one well-crafted packet with a maliciously crafted header. The result is an immediate out-of-memory condition within the Perl interpreter running the PSGI application.
The operational impact of this vulnerability is severe due to the architecture in which HTTP::Server::PSGI typically operates. Unlike multi-process or multi-threaded web servers that can isolate failures per connection, many deployments using HTTP::Server::PSGI run as a single process serving all requests sequentially. Consequently, when one request triggers an out-of-memory error and causes the Perl interpreter to crash, the entire server instance terminates abruptly. This leads to a complete denial of service for all users attempting to access the application hosted by that specific worker or daemon. The only way to restore availability is through manual intervention to restart the server process, resulting in significant downtime and potential data loss if stateful sessions are not persisted externally. Because this can be triggered with minimal network resources from the attacker's side, it serves as an efficient low-effort denial-of-service vector that does not require complex exploitation techniques or multiple concurrent connections.
This vulnerability aligns closely with CWE-400, which describes Uncontrolled Resource Consumption, specifically falling under scenarios where a server allocates excessive memory based on untrusted input without adequate bounds checking. Furthermore, in the context of the MITRE ATT&CK framework, this behavior is indicative of T1498 Network Denial of Service, as it involves using specific network inputs to disrupt service availability by exhausting system resources such as RAM or CPU cycles through inefficient allocation patterns rather than overwhelming bandwidth capacity. The lack of input sanitization for numeric fields like Content-Length allows the attacker to manipulate internal resource management routines directly.
To mitigate this vulnerability, organizations must upgrade HTTP::Server::PSGI to version 1.0056 or later where these memory allocation checks have been addressed and limits are properly enforced. In environments where immediate patching is not feasible, defensive measures should be implemented at the network perimeter using web application firewalls or reverse proxies such as Nginx or Apache mod_proxy. These front-end components can inspect incoming HTTP headers and reject requests with Content-Length values that exceed a predefined threshold before they ever reach the Perl backend process. Additionally, configuring system-level limits on memory usage per process via cgroups or ulimit settings can provide an additional layer of protection by preventing any single process from consuming all available RAM, thereby containing the blast radius of such exploitation attempts and allowing for quicker recovery through automatic restart mechanisms rather than manual intervention.