CVE-2026-53183 mptcp: allow subflow rcv wnd to shrink
A flaw in the Linux kernel MPTCP implementation allows remote attackers to cause a denial of service by exhausting receiver buffer memory.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-53183?
CVE-2026-53183 is a high-severity denial of service vulnerability in Linux kernel, published on 25 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official description
In the Linux kernel, the following vulnerability has been resolved:
mptcp: allow subflow rcv wnd to shrink
In MPTCP connection, the `window` field in the TCP header refers to the MPTCP-level rcv_nxt and it's right edge should not move backward. Such constraint is enforced at DSS option generation time.
At the same time, the TCP stack ensures independently that the TCP-level rcv wnd right's edge does not move backward. That in turn causes artificial inflating of the MPTCP rcv window when the incoming data is acked at the TCP level and is OoO in the MPTCP sequence space (or lands in the backlog).
As a consequence, the incoming traffic can exceed the receiver rcvbuf size even when the sender is not misbehaving.
Prevent such scenario forcibly allowing the TCP subflow to shrink the TCP-level rcv wnd regardless of the current netns setting.
Weakness: CWE-400
Which versions are affected by CVE-2026-53183?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-53183?
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-2026-53183 being exploited?
There is no known exploitation of CVE-2026-53183 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as AZL-90404, BELL-CVE-2026-53183, DEBIAN-CVE-2026-53183, GHSA-wxvq-pwv2-xpc3, ROOT-OS-DEBIAN-12-CVE-2026-53183, ROOT-OS-UBUNTU-2404-CVE-2026-53183 and 1 more.