CVE-2026-89407 jackson-core: quadratic backtracking in NumberInput.PATTERN_FLOAT via looksLikeValidNumber() enables ReDoS

What is CVE-2026-89407?

CVE-2026-89407 is a high-severity denial of service vulnerability in FasterXML jackson-core, published on 22 Sep 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

Official description

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.

Weakness: CWE-400, CWE-1333

Which versions are affected by CVE-2026-89407?

10 open source packages ship an affected version, including com.fasterxml.jackson.core:jackson-core and tools.jackson.core:jackson-core.

How do I fix CVE-2026-89407?

Upgrade com.fasterxml.jackson.core:jackson-core to a fixed version for your release line: 2.18.11, 2.21.7 or 2.22.3.

Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.

Is CVE-2026-89407 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-89407 exists.

Sources

• CVE record
• NVD
• OSV
• GitHub advisory
• How this page is made

Also known as CLEANSTART-2026-BF54172, CLEANSTART-2026-CS86865, CLEANSTART-2026-DR85611, CLEANSTART-2026-JK65929, CLEANSTART-2026-MS81723, CLEANSTART-2026-NA92074 and 88 more.