FasterXML jackson-core Number Input Validation NumberInput.looksLikeValidNumber incorrect regex

Summaryinfo

A vulnerability was found in FasterXML jackson-core. It has been declared as problematic. The impacted element is the function NumberInput.looksLikeValidNumber of the component Number Input Validation. Such manipulation leads to incorrect regex. This vulnerability is referenced as CVE-2026-89407. It is possible to launch the attack remotely. No exploit is available.

Detailsinfo

A vulnerability was found in FasterXML jackson-core (version now known) and classified as problematic. Affected by this issue is the function NumberInput.looksLikeValidNumber of the component Number Input Validation. The manipulation with an unknown input leads to a incorrect regex vulnerability. Using CWE to declare the problem leads to CWE-185. The product specifies a regular expression in a way that causes data to be improperly matched or compared. Impacted is availability. CVE summarizes:

NumberInput.looksLikeValidNumber() in FasterXML jackson-core pre-validates "stringified numbers" with two regular expressions: PATTERN_FLOAT ([+-]?[0-9]*[\.]?[0-9]+([eE][+-]?[0-9]+)?), present since 2.17.0, and PATTERN_FLOAT_TRAILING_DOT, added in 2.17.2. PATTERN_FLOAT places adjacent quantifiers over the same character class -- an optional [0-9]* run, an optional dot, then a required [0-9]+ run -- so input that ultimately fails to match forces Java's backtracking engine to retry every possible split point of the digit run.  Matching cost therefore grows with the square of the input length.  An attacker who can supply JSON that an application deserializes into a numeric target type reaches this method through jackson-databind's default String-to-number coercion (StdDeserializer and NumberDeserializers for BigDecimal, BigInteger, Double and Float).  Because StreamReadConstraints.maxStringLength defaults to 20,000,000 characters, no constraint bounds the input before it reaches the regex.  Testing by the reporter confirmed O(n^2) growth across five consecutive input-size doublings, with a single 160,000-character string consuming roughly 74 seconds in one call; a small number of concurrent requests of ordinary body size can therefore exhaust a server's request-handling thread pool.  The affected method does not exist before 2.17.0, so 2.16.x and earlier releases are not affected.  The fix replaces both regular expressions with a hand-rolled single-pass scan.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-89407 since 09/11/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $0-$5k at the moment (estimation calculated on 09/22/2026).

There is no information about possible countermeasures known. It may be suggested to replace the affected object with an alternative product.

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Productinfo

Type

• Programming Language Software

Vendor

• FasterXML

Name

• jackson-core

License

• open-source

Website

• Product: https://github.com/FasterXML/jackson-core/

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