Reactor Core DoS via Flux.windowTimeout fairBackpressure (3.8.6)
CVE-2026-47857 Published on August 26, 2026
Reactor Core windowTimeout fair-backpressure stream hang due to 20-bit index wrap-around
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
Vulnerability Analysis
CVE-2026-47857 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity, and a high impact on availability.
Weakness Type
Integer Overflow or Wraparound
The software performs a calculation that can produce an integer overflow or wraparound, when the logic assumes that the resulting value will always be larger than the original value. This can introduce other weaknesses when the calculation is used for resource management or execution control. An integer overflow or wraparound occurs when an integer value is incremented to a value that is too large to store in the associated representation. When this occurs, the value may wrap to become a very small or negative number. While this may be intended behavior in circumstances that rely on wrapping, it can have security consequences if the wrap is unexpected. This is especially the case if the integer overflow can be triggered using user-supplied inputs. This becomes security-critical when the result is used to control looping, make a security decision, or determine the offset or size in behaviors such as memory allocation, copying, concatenation, etc.
Products Associated with CVE-2026-47857
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Affected Versions
Spring Reactor Core:- Version 3.8.0, <= 3.8.6 is affected.
- Version 3.5.0, <= 3.7.19 is affected.
- Before and including 3.4.41 is affected.