CVE-2018-9838 in OCaml
Summary
by MITRE
The caml_ba_deserialize function in byterun/bigarray.c in the standard library in OCaml 4.06.0 has an integer overflow which, in situations where marshalled data is accepted from an untrusted source, allows remote attackers to cause a denial of service (memory corruption) or possibly execute arbitrary code via a crafted object.
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Analysis
by VulDB Data Team • 01/23/2020
The vulnerability identified as CVE-2018-9838 resides within the OCaml standard library's bigarray implementation, specifically in the caml_ba_deserialize function located in byterun/bigarray.c. This flaw represents a critical security issue that affects OCaml version 4.06.0 and potentially other versions within the same release line. The vulnerability manifests as an integer overflow condition that occurs during the deserialization process of bigarray objects, which are used to represent multi-dimensional arrays in the OCaml programming environment.
The technical nature of this vulnerability stems from inadequate bounds checking within the deserialization routine. When OCaml processes marshalled data containing crafted bigarray objects, the caml_ba_deserialize function fails to properly validate array dimensions and memory requirements before attempting to allocate memory for the reconstructed data structure. This integer overflow condition can lead to memory corruption when the system attempts to allocate memory based on malformed size parameters provided in the malicious input. The vulnerability's impact is particularly severe because it operates within the core marshalling infrastructure that handles data interchange between OCaml processes, making it applicable to any application that accepts serialized data from untrusted sources.
From an operational perspective, this vulnerability creates significant risk for systems relying on OCaml's marshalling capabilities for inter-process communication, data persistence, or network protocols. Attackers can exploit this flaw by crafting specially designed serialized objects that trigger the integer overflow during deserialization, potentially leading to either denial of service through memory corruption or more severe arbitrary code execution. The remote exploitation aspect means that systems processing network data, file transfers, or any form of external serialized input are vulnerable to this attack vector. The vulnerability aligns with CWE-190, which specifically addresses integer overflow conditions that can result in memory corruption and arbitrary code execution.
The attack surface for this vulnerability extends across any OCaml application that utilizes the standard library's marshalling functions, including web applications, network services, and distributed systems. Applications using OCaml's bigarray module for performance-critical numerical computations or data structures are particularly at risk when processing untrusted input. The vulnerability's classification under the ATT&CK framework would align with techniques involving code injection and privilege escalation through memory corruption, as attackers can manipulate the deserialization process to achieve arbitrary code execution on vulnerable systems. Organizations should consider this vulnerability as part of their broader security posture assessment when deploying OCaml-based solutions in production environments.
Mitigation strategies for CVE-2018-9838 primarily involve upgrading to OCaml version 4.06.1 or later, where the integer overflow has been addressed through proper bounds checking and input validation. System administrators should also implement strict input validation policies for any serialized data processing, particularly when dealing with external or untrusted sources. Additional protective measures include network segmentation, application sandboxing, and monitoring for unusual memory allocation patterns that might indicate exploitation attempts. The fix implemented in subsequent versions demonstrates proper defensive programming practices that align with security best practices for memory management and input validation in functional programming environments.