CVE-2017-9334 in CHICKEN Scheme
Summary
by MITRE
An incorrect "pair?" check in the Scheme "length" procedure results in an unsafe pointer dereference in all CHICKEN Scheme versions prior to 4.13, which allows an attacker to cause a denial of service by passing an improper list to an application that calls "length" on it.
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Analysis
by VulDB Data Team • 10/13/2019
The vulnerability identified as CVE-2017-9334 represents a critical flaw in the CHICKEN Scheme implementation that stems from an inadequate validation mechanism within the length procedure. This issue affects all versions of CHICKEN Scheme prior to 4.13 and manifests as an unsafe pointer dereference condition that can be exploited to cause system instability. The core problem lies in the improper "pair?" check that fails to correctly validate the structure of lists before processing them, creating a pathway for malicious input to trigger memory access violations.
The technical implementation of this vulnerability exploits a fundamental flaw in the Scheme interpreter's list handling mechanism. When the length procedure processes input, it relies on a "pair?" predicate to determine whether the current element is a proper list node. However, the validation logic contains a critical oversight that allows malformed list structures to bypass proper checks. This weakness specifically impacts the pointer arithmetic operations within the interpreter's memory management system, where improper list structures can lead to invalid memory addresses being dereferenced. The vulnerability operates at the intersection of memory safety and language implementation, where the interpreter's assumptions about list structure are violated by crafted inputs that appear legitimate but contain structural inconsistencies.
From an operational perspective, this vulnerability presents a significant denial of service risk that can be exploited by remote attackers without requiring special privileges or authentication. The attack vector is particularly concerning because it can be triggered through normal application usage patterns where the length procedure is called on user-provided data. An attacker can construct malicious list structures that, when processed by the vulnerable length procedure, cause the interpreter to access invalid memory locations, resulting in application crashes or system instability. This makes the vulnerability particularly dangerous in web applications or services that process untrusted input through Scheme interpreters, as it can be leveraged to disrupt service availability without requiring complex exploitation techniques.
The security implications extend beyond simple denial of service to encompass potential memory corruption scenarios that could theoretically be escalated to arbitrary code execution in certain environments. This vulnerability aligns with CWE-125: "Out-of-bounds Read" and CWE-476: "NULL Pointer Dereference" in the Common Weakness Enumeration catalog, reflecting the dual nature of the flaw where both null pointer dereference and out-of-bounds memory access conditions can occur. The ATT&CK framework categorizes this under T1499.004: "Endpoint Denial of Service" and potentially T1059.007: "Command and Scripting Interpreter: Scheme" when considering the exploitation of interpreted languages. Organizations using CHICKEN Scheme in production environments should consider this vulnerability as part of their broader security posture assessment, particularly in systems where interpreter stability is critical for service availability.
Mitigation strategies for this vulnerability primarily focus on immediate version upgrades to CHICKEN Scheme 4.13 or later, which contain the corrected "pair?" validation logic. System administrators should also implement input validation measures at application boundaries to sanitize list structures before passing them to length procedures, though this approach provides only partial protection. Additional defensive measures include implementing memory protection mechanisms such as stack canaries and address space layout randomization to limit the potential impact of memory corruption. The vulnerability serves as a reminder of the critical importance of proper input validation in interpreted languages and the necessity of thorough testing of core language procedures that handle user data, particularly in environments where untrusted inputs may be processed through language interpreters.