CVE-2026-18401
MediumCVSS 6.9Exploitation Probability (EPSS)
Low risk23th percentile - higher than 23% of all known CVEs
Summary
The non-blocking (asynchronous) JSON parser in jackson-core does not enforce the maxNumberLength constraint (default: 1000 characters) defined in StreamReadConstraints. An attacker can submit a number token of arbitrary length, leading to excessive memory allocation and potential CPU exhaustion, resulting in a denial of service (DoS). The issue affects jackson-core versions 2.15.0–2.18.5 and 2.19.0–2.21.0, as well as tools.jackson.core 3.0.0–3.0.x.
Risk Assessment
Organizations using applications based on the async parser (e.g., Spring WebFlux) are exposed to DoS attacks by sending JSON with an extremely long number, potentially causing OutOfMemoryError and significant CPU load. The attack requires no privileges or user interaction beyond the ability to submit data for parsing.
Recommendation
Immediately upgrade jackson-core to a patched version (e.g., 2.18.6 or later, 2.21.1 or later, and for 3.x to a fixed release). If upgrading is not possible, restrict access to the application or apply additional filters to limit the size of submitted data.
Other vulnerabilities in jackson-core
See all- CVE-2026-68494High
The fix for CVE-2026-18401 in jackson-core is incomplete and leaves a bypass in the non-blocking parser. An attacker can stream JSON in small chunks without a terminator, causing unbounded buffer growth limited only by maxStringLength (20 MiB) instead of maxNumberLength (1000).
- CVE-2026-29062High
In jackson-core versions 3.0.0 through 3.1.0, the UTF8DataInputJsonParser and ReaderBasedJsonParser bypass the maxNestingDepth constraint (default: 500) defined in StreamReadConstraints. This allows an attacker to supply a deeply nested JSON document, causing a StackOverflowError and Denial of Service (DoS). The issue is fixed in version 3.1.0.
Original NVD description (English source)
The non-blocking (asynchronous) JSON parser in jackson-core does not enforce the maxNumberLength constraint defined in StreamReadConstraints (default: 1000 characters). An attacker able to submit JSON to an application that uses the async parser API can supply a number token of arbitrary length, leading to excessive memory allocation and potential CPU exhaustion, resulting in a denial of service. The synchronous parser enforces this limit correctly, so the constraint is applied inconsistently depending on which parsing API the application uses. Root cause: the async parsing path in NonBlockingUtf8JsonParserBase and related classes never invokes the number length validation methods. Number parsing methods such as _finishNumberIntegralPart() accumulate digits into the TextBuffer without any length check, then call _valueComplete() to finalize the token. _valueComplete() does not call resetInt() or resetFloat(), which are the methods in ParserBase where validateIntegerLength() and validateFPLength() are performed. Because that validation step is skipped, maxNumberLength is never enforced on the async code path. Impact: an attacker sending a JSON document containing an arbitrarily long number to an application using the async parser (for example a Spring WebFlux or other reactive application) can cause unbounded allocation in the TextBuffer and an OutOfMemoryError. If the application subsequently calls getBigIntegerValue() or getDecimalValue(), the JVM may additionally be tied up in O(n^2) BigInteger parsing, causing CPU-based denial of service. No privileges or user interaction beyond the ability to submit data for parsing are required. This issue affects com.fasterxml.jackson.core:jackson-core from version 2.15.0 through 2.18.5 and from 2.19.0 through 2.21.0, and tools.jackson.core:jackson-core from 3.0.0 through 3.0.x. Versions prior to 2.15.0 are not affected, because StreamReadConstraints -- which defines the maxNumberLength setting -- was first introduced in jackson-core 2.15.0, so no such constraint exists to be bypassed in earlier releases. Note that GHSA-72hv-8253-57qq records the lower bound of the affected 2.x range as 2.0.0.