CVE-2026-31774 io_uring/net: fix slab-out-of-bounds read in io_bundle_nbufs()
A local attacker can trigger an integer overflow in the Linux kernel's io_uring subsystem, causing a slab-out-of-bounds read and potential system crash or memory leak.
- 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-2026-31774?
CVE-2026-31774 is a high-severity vulnerability in Linux kernel, published on 1 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:
io_uring/net: fix slab-out-of-bounds read in io_bundle_nbufs()
sqe->len is __u32 but gets stored into sr->len which is int. When userspace passes sqe->len values exceeding INT_MAX (e.g. 0xFFFFFFFF), sr->len overflows to a negative value. This negative value propagates through the bundle recv/send path:
1. io_recv(): sel.val = sr->len (ssize_t gets -1) 2. io_recv_buf_select(): arg.max_len = sel->val (size_t gets 0xFFFFFFFFFFFFFFFF) 3. io_ring_buffers_peek(): buf->len is not clamped because max_len is astronomically large 4. iov[].iov_len = 0xFFFFFFFF flows into io_bundle_nbufs() 5. io_bundle_nbufs(): min_t(int, 0xFFFFFFFF, ret) yields -1, causing ret to increase instead of decrease, creating an infinite loop that reads past the allocated iov[] array
This results in a slab-out-of-bounds read in io_bundle_nbufs() from the kmalloc-64 slab, as nbufs increments past the allocated iovec entries.
BUG: KASAN: slab-out-of-bounds in io_bundle_nbufs+0x128/0x160 Read of size 8 at addr ffff888100ae05c8 by task exp/145 Call Trace: io_bundle_nbufs+0x128/0x160 io_recv_finish+0x117/0xe20 io_recv+0x2db/0x1160
Fix this by rejecting negative sr->len values early in both io_sendmsg_prep() and io_recvmsg_prep(). Since sqe->len is __u32, any value > INT_MAX indicates overflow and is not a valid length.
Which versions are affected by CVE-2026-31774?
It affects 1 product.
Products include Linux kernel.
How do I fix CVE-2026-31774?
Apply the vendor's patch.
Is CVE-2026-31774 being exploited?
There is no known exploitation of CVE-2026-31774 in the wild and no public exploit code.
Other vulnerabilities in Linux kernel
Sources
Also known as BELL-CVE-2026-31774, DEBIAN-CVE-2026-31774, GHSA-w3xc-h2ch-2q3q, UBUNTU-CVE-2026-31774.