CVE-2026-53191
HighCVSS 7.8Exploitation Probability (EPSS)
Low risk4th percentile - higher than 4% of all known CVEs
Summary
In the Linux kernel's io_uring/net subsystem, a vulnerability was found due to improper inheritance of the IORING_CQE_F_BUF_MORE flag during bundle recv retries. The flag was missing from the CQE_F_MASK, causing it to be dropped and leading to incorrect buffer management by userspace.
Risk Assessment
The organization is at risk of incorrect operation of provided buffer rings in incremental mode, potentially causing data corruption or application crashes in software using io_uring.
Recommendation
Immediately update the Linux kernel to a version containing the fix (commit adding IORING_CQE_F_BUF_MORE to CQE_F_MASK). Until updated, avoid using bundle recv with incremental buffer rings.
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Original NVD description (English source)
In the Linux kernel, the following vulnerability has been resolved: io_uring/net: inherit IORING_CQE_F_BUF_MORE across bundle recv retries When a bundle recv retries inside io_recv_finish(), the merge logic OR the saved cflags from the previous iteration with the cflags returned by the new iteration: cflags = req->cqe.flags | (cflags & CQE_F_MASK); Bits listed in CQE_F_MASK are inherited from the new iteration, and all other bits (notably IORING_CQE_F_BUFFER and the buffer ID) come from the saved cflags. Before this change CQE_F_MASK covered only IORING_CQE_F_SOCK_NONEMPTY and IORING_CQE_F_MORE. When using provided buffer rings (IOU_PBUF_RING_INC) with incremental mode, and bundle recv, io_kbuf_inc_commit() can leave the head ring entry partially consumed, __io_put_kbufs() then sets IORING_CQE_F_BUF_MORE on the returned cflags so userspace knows the buffer ID will be reused for subsequent completions. Because IORING_CQE_F_BUF_MORE was not in CQE_F_MASK, the merge above silently dropped it whenever the final retry iteration partially consumed the buffer, and the subsequent req->cqe.flags = cflags & ~CQE_F_MASK save would have left a stale IORING_CQE_F_BUF_MORE in the carried-over cflags had one been present. Userspace would then wrongfully advance it ring head past an entry the kernel still uses. Add IORING_CQE_F_BUF_MORE to CQE_F_MASK so it is both inherited from the new iteration into the user-visible CQE and stripped from the saved cflags between iterations.