CVE-2026-68914 in Mojolicious
Summary
by MITRE • 09/18/2026
Mojolicious is a real-time web framework for Perl. Prior to 9.47, the pure-Perl implementation of Mojo::JSON does not limit nesting depth when Cpanel::JSON::XS is unavailable or MOJO_NO_JSON_XS is enabled. An attacker who can supply untrusted JSON to decode_json, from_json, or j can submit deeply nested arrays or objects, causing unbounded recursion, memory exhaustion, and a process crash. Applications using the Cpanel::JSON::XS backend are not affected because that backend already enforces a nesting limit. This issue is fixed in version 9.47.
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Analysis
by VulDB Data Team • 09/18/2026
The vulnerability identified in Mojolicious versions prior to 9.47 represents a critical resource exhaustion flaw within its JSON parsing subsystem, specifically affecting the pure-Perl implementation of Mojo::JSON. As a real-time web framework for Perl, Mojolicious frequently processes incoming data payloads that are formatted as JavaScript Object Notation (JSON). The core issue arises when the application is configured to use or falls back to the native Perl-based JSON parser rather than the optimized Cpanel::JSON::XS module. This scenario can occur either because Cpanel::JSON::XS is not installed in the environment or if the MOJO_NO_JSON_XS environment variable is explicitly enabled, forcing the framework to rely on its internal pure-Perl fallback implementation for decoding operations such as decode_json, from_json, and j.
The technical root cause of this vulnerability lies in the absence of a recursion depth limit within the pure-Perl JSON decoder. When an attacker supplies untrusted JSON input containing deeply nested arrays or objects, the parser attempts to traverse these structures recursively without any safeguard against excessive nesting levels. This lack of constraint leads directly to unbounded recursion, where each level of nesting consumes additional stack space and memory resources on the server process. As the depth increases, the application rapidly exhausts available system memory and CPU cycles, resulting in a denial-of-service condition characterized by severe performance degradation or complete process crash.
From an operational perspective, this flaw allows for remote resource exhaustion attacks against any Mojolicious-based web service that accepts JSON input via API endpoints, form submissions, or other data ingestion points. An attacker can craft malicious payloads with extreme nesting depths to trigger the vulnerability remotely over HTTP/S. The impact is significant as it compromises the availability of the affected application and potentially destabilizes the underlying server infrastructure if multiple concurrent attacks are launched against resource-constrained environments. This type of attack aligns with common patterns observed in distributed denial-of-service campaigns targeting web frameworks, where attackers exploit parsing logic flaws to amplify their impact without requiring authentication or high privilege levels.
This vulnerability is categorized under CWE-787: Out-of-bounds Write and more specifically relates to CWE-400: Uncontrolled Resource Consumption due to the unbounded recursion leading to memory exhaustion. In terms of offensive security frameworks, this behavior corresponds to ATT&CK technique T1496: Resource Hijacking, where an adversary uses computing resources for their own purposes by exhausting system capacity through inefficient or malicious code execution paths. The attack vector is classified as Network (ATT&CK T1078) if the service is exposed externally, leveraging standard web protocols to deliver the malformed JSON payload.
The recommended mitigation strategy involves upgrading Mojolicious to version 9.47 or later, where the pure-Perl implementation has been patched to enforce a reasonable nesting depth limit during parsing operations. For organizations unable to immediately upgrade their production environments due to dependency constraints, temporary mitigations include implementing input validation and size limits at the reverse proxy or load balancer level before requests reach the Mojolicious application server. Additionally, ensuring that Cpanel::JSON::XS is installed and available in the Perl library path will cause Mojolicious to bypass the vulnerable pure-Perl implementation entirely, as this backend already enforces strict nesting limits by design. Regular security audits of third-party dependencies and continuous monitoring for anomalous memory usage patterns can also help detect attempts to exploit such resource exhaustion vulnerabilities early.