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VulnerabilityPublished

CVE-2026-18401: FasterXML jackson-core · Unthrottled Resource Allocation

Affects FasterXML jackson-coreSource CVE Database V5

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Not known to be exploited · CVSS 6.9 Medium : upgrade to 2.21.1 when convenient.

Data as of 2 Nov 2026, 22:58 UTC

CVSS 4.0 base score
6.9Medium
How severe the flaw is on the 0–10 CVSS scale.
EPSS
0.4% chance of exploitation in 30 days – higher than 35% of CVEsExploit Prediction Scoring System: the likelihood attackers will use this flaw soon.
Patch
Available – fixed in 2.21.1, 3.1.0
CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N

Exploitation evidence

  1. Disclosed: evidence found.

    CVE published 4 Aug 2026

  2. Detectable: no evidence on record.

    No public nuclei template indexed

  3. Weaponized: no evidence on record.

    No public exploit code indexed in Metasploit or Exploit-DB

  4. Exploited in the wild: no evidence on record.

    Not in CISA KEV and no source reports exploitation

  5. Observed by OffSeq Mirage: no evidence on record.

    No attack traffic recorded by OffSeq Mirage sensors

A missing step is not evidence of safety. Sources: cve.org (opens in a new tab), the Metasploit, Exploit-DB and nuclei-templates index as of 2 Nov 2026.

What to do

Upgrade jackson-core and FasterXML/com.fasterxml.jackson.core:jackson-core to 2.21.1; jackson-core and FasterXML/tools.jackson.core:jackson-core to 3.1.0.

Affected software

ProductAffectedFixed in
FasterXMLjackson-coreAffected
  • >=2.15.0 <=2.18.5
  • >=2.19.0 <2.21.1
Fixed in
  • 2.21.1
FasterXMLjackson-coreAffected
  • >=3.0.0 <3.1.0
Fixed in
  • 3.1.0
MavenFasterXML/com.fasterxml.jackson.core:jackson-corepkg:maven/FasterXML/com.fasterxml.jackson.core:jackson-coreOther threatsAffected
  • >=2.15.0 <=2.18.5
  • >=2.19.0 <2.21.1
Fixed in
  • 2.21.1
MavenFasterXML/tools.jackson.core:jackson-corepkg:maven/FasterXML/tools.jackson.core:jackson-coreOther threatsAffected
  • >=3.0.0 <3.1.0
Fixed in
  • 3.1.0

Check your own hosts for these packages with threat-finder (opens in a new tab), our free open-source scanner.

AI-suggested

If you cannot patch yet, applications using the asynchronous jackson-core parser should consider avoiding the async parser API or implement application-level limits on JSON number token lengths. Monitoring and filtering input JSON to reject excessively long number tokens can mitigate the risk.

Description

CVE-2026-18401 is a medium severity vulnerability in FasterXML jackson-core affecting the asynchronous JSON parser. The async parser does not enforce the maxNumberLength constraint, allowing an attacker to submit JSON with arbitrarily long number tokens. This leads to excessive memory allocation and potential CPU exhaustion, causing denial of service. The synchronous parser is not affected as it enforces this limit correctly. No privileges or user interaction beyond submitting JSON data are required. The issue affects jackson-core versions 2.15.0 through 2.18.5, 2.19.0 through 2.21.0, and 3.0.0 through 3.0.x.

References

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