CVE-2026-95155 in Jackson
Summary
by MITRE • 10/15/2026
FasterXML Jackson 1.x, confirmed in jackson-mapper-asl versions 1.8.3, 1.9.2, 1.9.11, 1.9.12, and 1.9.13, allows attackers to cause a denial of service by supplying deeply nested JSON input to an application that deserializes untrusted JSON using ObjectMapper.readValue.
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Analysis
by VulDB Data Team • 10/15/2026
The vulnerability identified in FasterXML Jackson versions within the 1.x series, specifically affecting jackson-mapper-asl releases such as 1.8.3 and various patches up through 1.9.13, represents a critical risk to applications that process untrusted JSON data. This flaw is rooted in the way the library handles recursive structures during deserialization when utilizing the ObjectMapper.readValue method. When an attacker supplies a JSON payload containing deeply nested objects or arrays, the underlying processing logic triggers excessive recursion within the parser and object mapper components. Because the library does not enforce strict limits on nesting depth by default in these older versions, it fails to detect or abort execution before resource exhaustion occurs. This behavior allows malicious actors to exploit the lack of input validation regarding structural complexity rather than content validity alone.
From a technical perspective, this issue is classified under CWE-400, which denotes Uncontrolled Resource Consumption. The specific mechanism involves the recursive descent into nested data structures during the conversion of JSON text into Java objects. Each level of nesting consumes stack space and processing cycles on the server side. As the depth increases exponentially relative to input size in certain parsing scenarios, the application thread becomes blocked or crashes due to a StackOverflowError or out-of-memory conditions. This is not merely an efficiency issue but a fundamental failure in handling untrusted inputs that can lead to complete service disruption for any endpoint relying on this deserialization logic without additional safeguards.
The operational impact of this vulnerability is severe, primarily manifesting as a Denial of Service against the affected application infrastructure. Attackers do need complex exploits or authentication bypasses; they simply need to send a relatively small but deeply nested JSON string to an exposed API or web service that uses Jackson for parsing. The resulting resource exhaustion can take down individual server instances or contribute to broader system instability if multiple requests are sent in parallel. This makes it particularly dangerous in high-throughput environments where automated scanners might inadvertently trigger the condition, or where malicious actors deliberately target these endpoints to disrupt business operations without needing to inject code or exfiltrate data directly through this specific vector.
Mitigation strategies for organizations still running legacy versions of Jackson must prioritize immediate upgrades if feasible. The recommended path is to migrate to a supported version of FasterXML Jackson that includes built-in protections against deep nesting, such as the ability to configure maximum tree depth limits via MapperFeature or JsonParser settings. For applications unable to upgrade immediately due to compatibility constraints with older Java environments, developers should implement custom input validation layers before passing JSON strings to the ObjectMapper. This can involve parsing the raw string first using a lightweight parser that checks for excessive nesting levels and rejecting payloads that exceed defined thresholds. Additionally, deploying Web Application Firewalls configured to detect abnormally deep JSON structures or limiting request payload sizes can provide an additional layer of defense against exploitation attempts targeting this specific weakness in older software stacks.