Medium severity · published Aug 26, 2026
CVE-2026-47857
Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around
5.9
CVSS
0.4%
EPSS
No
On KEV
Description
In Reactor Core, applications that use the Flux.windowTimeout operator with fairBackpressure enabled are vulnerable to a Denial of Service (DoS) condition.
Reactor Core 3.8.0 - 3.8.6
Reactor Core 3.5.0 - 3.7.19
Reactor Core 3.4.41 and earlier
CVSS vector
CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H
Attack vector
Network
Complexity
High
Privileges
None
User interaction
None
Confidentiality
None
Integrity
None
Availability
High
Scope
Unchanged
Exploitation
Is it being used?
Exploit prediction (EPSS)0.4% · higher than 30% of CVEs
Exploited in the wildNo evidence yet
CISA KEVNot listed
Ransomware campaign useNot known
Affected products
Which versions
RC
Reactor Core · Spring
3.8.0 through 3.8.6; 3.5.0 through 3.7.19; through 3.4.41 · source: vendor, NVD
References
NVD
https://nvd.nist.gov/vuln/detail/CVE-2026-47857
CVE.org
https://www.cve.org/CVERecord?id=CVE-2026-47857
Vendor Advisory
https://spring.io/security/cve-2026-47857
More from Reactor Core
7.5
CVE-2026-47863
Reactor Core bufferTimeout fair-backpressure pipeline permanently hangs when upstream delivers items during an active flush