CVE-2026-87734 in utcp
Summary
by MITRE • 09/09/2026
An issue was discovered in the utcp package before 0.0.6 for OCaml. Out-of-order segment reassembly allows remote denial of service.
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Analysis
by VulDB Data Team • 09/09/2026
The vulnerability identified within the utcp package, specifically affecting versions prior to 0.0.6 for the OCaml programming language, represents a critical flaw in the implementation of TCP stream reassembly logic. This software component is responsible for reconstructing data streams from individual network packets received over an internet connection. The core technical deficiency lies in how the library handles segments that arrive out of their expected sequence order. In standard Transmission Control Protocol operations, it is common for packets to be reordered during transit due to varying network paths or congestion. A robust TCP implementation must maintain a buffer and correctly reorder these segments before passing the reconstructed data stream to the application layer. However, in this specific version of utcp, the reassembly mechanism fails to properly manage out-of-order arrival scenarios, leading to internal state corruption or infinite loops within the processing logic.
This flaw directly enables a remote denial of service attack against any application utilizing the vulnerable library. An attacker can exploit this by sending a series of TCP segments with manipulated sequence numbers that force the utcp implementation into an erroneous state. Because the reassembly process does not correctly handle these out-of-order inputs, it may result in excessive memory consumption or CPU exhaustion as the system attempts to resolve the malformed stream structure. In some implementations, such logic errors can also lead to crashes of the host application process. The impact is severe because it allows an unauthenticated remote adversary to disrupt service availability without needing any prior access credentials or successful authentication steps.
From a classification perspective, this vulnerability aligns with CWE-400, which denotes Uncontrolled Resource Consumption, as the flaw leads to resource exhaustion through improper handling of input data. It also relates to CWE-20, Improper Input Validation, since the library fails to validate and correctly process sequence numbers that fall outside expected bounds during reassembly. In terms of offensive security frameworks, this exploit technique falls under MITRE ATT&CK T1499, Endpoint Denial of Service, specifically involving resource exhaustion via application layer protocols. The attack vector is classified as Network (ATT&CK T1078) or Remote (T1133), depending on the specific deployment context and network accessibility of the target service.
Mitigation strategies for this vulnerability are primarily focused on immediate software updates. Organizations running applications that depend on utcp must upgrade to version 0.0.6 or later, where the reassembly logic has been corrected to properly handle out-of-order segments. For environments where an immediate patch is not feasible, network-level controls such as intrusion prevention systems can be configured to detect and block anomalous TCP traffic patterns indicative of this exploitation attempt. Additionally, implementing rate limiting on incoming connections can help mitigate the impact by reducing the volume of malicious packets that reach the vulnerable application layer. Developers should also review their dependency management processes to ensure timely updates of third-party libraries used in production environments.