CVE-2026-18401: FasterXML jackson-core · Unthrottled Resource Allocation
Affects FasterXML jackson-coreSource CVE Database V5
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
- 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:NExploitation evidence
Disclosed: evidence found.
CVE published 4 Aug 2026
Detectable: no evidence on record.
No public nuclei template indexed
Weaponized: no evidence on record.
No public exploit code indexed in Metasploit or Exploit-DB
Exploited in the wildExploited: no evidence on record.
Not in CISA KEV and no source reports exploitation
Observed by OffSeq MirageSeen by 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
| Product | Affected | Fixed in |
|---|---|---|
| FasterXMLjackson-core | Affected
| Fixed in
|
| FasterXMLjackson-core | Affected
| Fixed in
|
MavenFasterXML/com.fasterxml.jackson.core:jackson-corepkg:maven/FasterXML/com.fasterxml.jackson.core:jackson-coreOther threats | Affected
| Fixed in
|
MavenFasterXML/tools.jackson.core:jackson-corepkg:maven/FasterXML/tools.jackson.core:jackson-coreOther threats | Affected
| Fixed in
|
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.