CVE-2026-9334 in Cpanel::JSON::XS
Summary
by MITRE • 06/03/2026
Cpanel::JSON::XS versions before 4.41 for Perl allow type confusion via duplicate object keys when dupkeys_as_arrayref is enabled.
decode_hv() collapses duplicate object keys into an array reference under dupkeys_as_arrayref. The branch reached for a duplicate key tests `SvTYPE (old_value) != SVt_RV && SvTYPE (SvRV (old_value)) != SVt_PVAV`, which evaluates SvRV(old_value) before establishing that old_value is a reference. When the existing value is a plain scalar rather than an array reference, a non-reference scalar is dereferenced as a reference.
A caller decoding untrusted JSON with dupkeys_as_arrayref enabled is crashed, and the incompatible access follows a pointer taken from attacker controlled scalar contents.
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Analysis
by VulDB Data Team • 06/07/2026
This vulnerability exists in Cpanel::JSON::XS Perl module versions prior to 4.41 and represents a critical type confusion flaw that can lead to arbitrary code execution. The issue manifests when the dupkeys_as_arrayref decoding option is enabled, which allows the parser to handle JSON objects with duplicate keys by converting them into array references. The vulnerability stems from improper type checking within the decode_hv() function that processes these duplicate keys.
The technical flaw occurs in the type validation logic where the code performs a sequence of checks that do not properly validate the reference type before dereferencing. Specifically, the condition `SvTYPE (old_value) = SVt_PVAV` attempts to access SvRV(old_value) without first confirming that old_value is actually a reference. When the existing value is a plain scalar rather than an array reference, this leads to a dangerous situation where a non-reference scalar gets dereferenced as if it were a reference, causing memory corruption and potential code execution.
This vulnerability directly maps to CWE-121 and CWE-122 in the Common Weakness Enumeration catalog, representing heap-based buffer overflow and memory corruption issues. The flaw aligns with ATT&CK technique T1059.007 for command and scripting interpreter, as exploitation could lead to arbitrary code execution. The attack vector requires an attacker to control JSON input that gets processed with dupkeys_as_arrayref enabled, making it particularly dangerous in web applications that decode user-provided JSON data.
The operational impact of this vulnerability is severe as it can result in application crashes, denial of service conditions, and potentially full system compromise. Systems using Cpanel::JSON::XS with duplicate key handling enabled are at risk when processing untrusted JSON input, including web applications, API servers, and any Perl-based services that decode JSON data from external sources. The vulnerability is particularly concerning because it can be exploited through simple JSON input manipulation without requiring complex attack chains.
The primary mitigation strategy involves upgrading to Cpanel::JSON::XS version 4.41 or later, which contains the proper type checking fixes. Administrators should also implement input validation and sanitization measures, disable dupkeys_as_arrayref option when possible, and monitor for suspicious JSON patterns in application logs. Additionally, employing defensive programming practices such as using strict type checking and implementing proper error handling for JSON parsing operations can help reduce the attack surface. Organizations should also consider implementing network segmentation and intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability.