# CVE-2021-47196: RDMA/core: Set send and receive CQ before forwarding to the driver

> A use-after-free vulnerability in the Linux kernel RDMA core allows local attackers to execute arbitrary code or escalate privileges via crafted QP creation requests.

- **Severity:** High 7.8 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **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:** Yes
- **Published:** 10 Apr 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-47196, GHSA-j2j3-mjcj-v75r, UBUNTU-CVE-2021-47196

## What is CVE-2021-47196?

CVE-2021-47196 is a high-severity use after free vulnerability in Linux kernel, published on 10 Apr 2024. 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:

RDMA/core: Set send and receive CQ before forwarding to the driver

Preset both receive and send CQ pointers prior to call to the drivers and
overwrite it later again till the mlx4 is going to be changed do not
overwrite ibqp properties.

This change is needed for mlx5, because in case of QP creation failure, it
will go to the path of QP destroy which relies on proper CQ pointers.

 BUG: KASAN: use-after-free in create_qp.cold+0x164/0x16e [mlx5_ib]
 Write of size 8 at addr ffff8880064c55c0 by task a.out/246

 CPU: 0 PID: 246 Comm: a.out Not tainted 5.15.0+ #291
 Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS rel-1.13.0-0-gf21b5a4aeb02-prebuilt.qemu.org 04/01/2014
 Call Trace:
  dump_stack_lvl+0x45/0x59
  print_address_description.constprop.0+0x1f/0x140
  kasan_report.cold+0x83/0xdf
  create_qp.cold+0x164/0x16e [mlx5_ib]
  mlx5_ib_create_qp+0x358/0x28a0 [mlx5_ib]
  create_qp.part.0+0x45b/0x6a0 [ib_core]
  ib_create_qp_user+0x97/0x150 [ib_core]
  ib_uverbs_handler_UVERBS_METHOD_QP_CREATE+0x92c/0x1250 [ib_uverbs]
  ib_uverbs_cmd_verbs+0x1c38/0x3150 [ib_uverbs]
  ib_uverbs_ioctl+0x169/0x260 [ib_uverbs]
  __x64_sys_ioctl+0x866/0x14d0
  do_syscall_64+0x3d/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae

 Allocated by task 246:
  kasan_save_stack+0x1b/0x40
  __kasan_kmalloc+0xa4/0xd0
  create_qp.part.0+0x92/0x6a0 [ib_core]
  ib_create_qp_user+0x97/0x150 [ib_core]
  ib_uverbs_handler_UVERBS_METHOD_QP_CREATE+0x92c/0x1250 [ib_uverbs]
  ib_uverbs_cmd_verbs+0x1c38/0x3150 [ib_uverbs]
  ib_uverbs_ioctl+0x169/0x260 [ib_uverbs]
  __x64_sys_ioctl+0x866/0x14d0
  do_syscall_64+0x3d/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae

 Freed by task 246:
  kasan_save_stack+0x1b/0x40
  kasan_set_track+0x1c/0x30
  kasan_set_free_info+0x20/0x30
  __kasan_slab_free+0x10c/0x150
  slab_free_freelist_hook+0xb4/0x1b0
  kfree+0xe7/0x2a0
  create_qp.part.0+0x52b/0x6a0 [ib_core]
  ib_create_qp_user+0x97/0x150 [ib_core]
  ib_uverbs_handler_UVERBS_METHOD_QP_CREATE+0x92c/0x1250 [ib_uverbs]
  ib_uverbs_cmd_verbs+0x1c38/0x3150 [ib_uverbs]
  ib_uverbs_ioctl+0x169/0x260 [ib_uverbs]
  __x64_sys_ioctl+0x866/0x14d0
  do_syscall_64+0x3d/0x90
  entry_SYSCALL_64_after_hwframe+0x44/0xae

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2021-47196?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47196?

Apply the vendor's patch.

## Is CVE-2021-47196 being exploited?

There is no known exploitation of CVE-2021-47196 in the wild and no public exploit code.

## Other vulnerabilities in Linux kernel

- [CVE-2026-53266](https://insights.sbomify.com/CVE-2026-53266/): Linux Kernel Out-of-Bounds Write (high 8.8, exploited in the wild)
- [CVE-2013-6282](https://insights.sbomify.com/CVE-2013-6282/): Linux Kernel Improper Input Validation (high 8.8, exploited in the wild)
- [CVE-2022-0185](https://insights.sbomify.com/CVE-2022-0185/): Linux Kernel Heap-Based Buffer Overflow (high 8.4, exploited in the wild)
- [CVE-2013-2094](https://insights.sbomify.com/CVE-2013-2094/): Linux Kernel Privilege Escalation (high 8.4, exploited in the wild)
- [CVE-2026-53362](https://insights.sbomify.com/CVE-2026-53362/): Linux Kernel Unspecified (high 7.8, exploited in the wild)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2021-47196 and fix it if it is affected.

What it is: CVE-2021-47196 is a high-severity use after free vulnerability in Linux kernel, published on 10 Apr 2024. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-47196 in the wild and no public exploit code.

Affected product: Linux kernel. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2021-47196/ (Markdown: https://insights.sbomify.com/CVE-2021-47196/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47196
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47196
- OSV: https://osv.dev/vulnerability/CVE-2021-47196

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47196/
Summaries are generated and may contain mistakes; the official description above is the record.