CVE-2026-45889 mptcp: do not account for OoO in mptcp_rcvbuf_grow()
A race condition in the Linux kernel MPTCP implementation can cause a divide-by-zero error, leading to a system crash.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-45889?
CVE-2026-45889 is a medium-severity denial of service vulnerability in Linux kernel, published on 27 May 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mptcp: do not account for OoO in mptcp_rcvbuf_grow()
MPTCP-level OoOs are physiological when multiple subflows are active concurrently and will not cause retransmissions nor are caused by drops.
Accounting for them in mptcp_rcvbuf_grow() causes the rcvbuf slowly drifting towards tcp_rmem[2].
Remove such accounting. Note that subflows will still account for TCP-level OoO when the MPTCP-level rcvbuf is propagated.
This also closes a subtle and very unlikely race condition with rcvspace init; active sockets with user-space holding the msk-level socket lock, could complete such initialization in the receive callback, after that the first OoO data reaches the rcvbuf and potentially triggering a divide by zero Oops.
Weakness: CWE-369
Which versions are affected by CVE-2026-45889?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-45889?
Apply the vendor's patch.
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-2026-45889 being exploited?
There is no known exploitation of CVE-2026-45889 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-45889, DEBIAN-CVE-2026-45889, GHSA-gh29-fq9g-3p7h, UBUNTU-CVE-2026-45889.