CVE-2026-89407: jackson-core: quadratic backtracking in NumberInput.PATTERN_FLOAT via looksLikeValidNumber() enables ReDoS
NumberInput.looksLikeValidNumber() in FasterXML jackson-core pre-validates "stringified numbers" with two regular expressions: PATTERNFLOAT ([+-]?[0-9][\.]?[0-9]+([eE][+-]?[0-9]+)?), present since 2.17.0, and PATTERNFLOATTRAILINGDOT, added in 2.17.2. PATTERNFLOAT 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
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com.fasterxml.jackson.core:jackson-coreto a version that resolves this vulnerability.Fixed in 2.18.11 - Upgrade
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com.fasterxml.jackson.core:jackson-coreto a version that resolves this vulnerability.Fixed in 2.21.7 - Upgrade
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com.fasterxml.jackson.core:jackson-coreto a version that resolves this vulnerability.Fixed in 2.22.3 - Upgrade
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tools.jackson.core:jackson-coreto a version that resolves this vulnerability.Fixed in 3.1.7 - Upgrade
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tools.jackson.core:jackson-coreto a version that resolves this vulnerability.Fixed in 3.2.2
Event History
Frequently Asked Questions
Which application paths are exposed to this issue?
Applications are exposed when they deserialize attacker-controlled JSON into BigDecimal, BigInteger, Double, or Float target types. jackson-databind's default String-to-number coercion reaches the affected jackson-core validation method on those paths.
What does an attacker need to trigger the denial of service?
An attacker needs to be able to supply JSON that the application deserializes into a numeric target type. A long digit-heavy string that ultimately fails the floating-number pattern can force quadratic regex backtracking; no privileges or user interaction are required according to the supplied vector.
Does the default string-length constraint prevent exploitation?
No. StreamReadConstraints.maxStringLength defaults to 20,000,000 characters, and the affected regex is reached before that default limit provides a useful bound on the backtracking work. The reported testing found that one 160,000-character string consumed roughly 74 seconds in a single call.