CVE-2020-9861 in Swift
Summary
by MITRE • 11/03/2020
A stack overflow issue existed in Swift for Linux. The issue was addressed with improved input validation for dealing with deeply nested malicious JSON input.
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Analysis
by VulDB Data Team • 12/01/2020
The vulnerability CVE-2020-9861 represents a critical stack overflow condition that affected Swift for Linux implementations, specifically manifesting during JSON parsing operations. This issue stems from inadequate input validation mechanisms within the Swift runtime environment when processing malformed or maliciously constructed JSON data structures. The flaw allows attackers to exploit deeply nested JSON inputs that exceed safe stack allocation limits, potentially leading to application crashes or more severe security implications.
The technical root cause of this vulnerability aligns with CWE-121, which describes stack-based buffer overflow conditions occurring when insufficient bounds checking is performed on stack memory allocations. In Swift for Linux, the JSON parsing routine fails to implement proper recursion depth limits or stack usage monitoring when encountering nested data structures. This allows malicious actors to craft JSON payloads with excessive nesting levels that consume all available stack space, resulting in stack overflow conditions that can be exploited for denial of service attacks or potentially arbitrary code execution depending on the system configuration.
From an operational perspective, this vulnerability presents significant risks to applications that rely on Swift for Linux for processing untrusted JSON data inputs. Systems utilizing Swift web services, API gateways, or backend processing components that accept JSON payloads from external sources become vulnerable to exploitation. The impact extends beyond simple application crashes as the vulnerability can be leveraged for persistent denial of service attacks against critical infrastructure services. Attackers can systematically target applications by submitting increasingly nested JSON structures until the stack overflow occurs, effectively rendering the service unavailable to legitimate users.
The mitigation strategy for CVE-2020-9861 involves implementing enhanced input validation mechanisms that establish strict limits on JSON nesting depth and overall payload size. System administrators should update their Swift runtime environments to versions that include the patched input validation routines. Organizations should also implement JSON parsing restrictions at the application level, including configuring maximum nesting limits and implementing proper error handling for malformed inputs. The fix addresses the underlying issue by introducing recursion depth checking and stack usage monitoring within the Swift JSON parsing libraries, preventing malicious inputs from consuming excessive stack resources. Security teams should monitor for potential exploitation attempts and consider implementing additional network-level controls to restrict JSON payload sizes and complexity. This vulnerability demonstrates the importance of input validation in modern programming environments and aligns with ATT&CK technique T1203, which covers exploitation of input validation weaknesses to achieve system compromise or denial of service conditions.