# CVE-2026-52939: net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion

> An unprivileged user can trigger a kernel panic via a NULL pointer dereference in the RDS/IB module by sending a masked atomic completion message.

- **Severity:** Medium 5.5 (`CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/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:** 24 Jun 2026
- **Updated:** 24 Jun 2026
- **Also known as:** BELL-CVE-2026-52939, DEBIAN-CVE-2026-52939, GHSA-v4gx-744x-jr2m, ROOT-OS-DEBIAN-11-CVE-2026-52939, ROOT-OS-DEBIAN-12-CVE-2026-52939, ROOT-OS-UBUNTU-2204-CVE-2026-52939, ROOT-OS-UBUNTU-2404-CVE-2026-52939, UBUNTU-CVE-2026-52939

## What is CVE-2026-52939?

CVE-2026-52939 is a medium-severity vulnerability in Linux kernel, published on 24 Jun 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:

net/rds: fix NULL deref in rds_ib_send_cqe_handler() on masked atomic completion

rds_ib_xmit_atomic() always programs a masked atomic opcode
(IB_WR_MASKED_ATOMIC_CMP_AND_SWP or IB_WR_MASKED_ATOMIC_FETCH_AND_ADD)
for every RDS atomic cmsg.  But the completion-side switch in
rds_ib_send_unmap_op() only handles the non-masked opcodes, so a masked
atomic completion falls through to default and returns rm == NULL while
send->s_op is left set.  rds_ib_send_cqe_handler() then dereferences the
NULL rm via rm->m_final_op, oopsing in softirq context.  An unprivileged
AF_RDS sendmsg() of an atomic cmsg over an active RDS/IB connection
triggers it; on hardware that natively accepts masked atomics (mlx4,
mlx5) no extra setup is needed.

  RDS/IB: rds_ib_send_unmap_op: unexpected opcode 0xd in WR!
  Oops: general protection fault [#1] SMP KASAN
  KASAN: null-ptr-deref in range [0x0000000000000190-0x0000000000000197]
  RIP: rds_ib_send_cqe_handler+0x25c/0xb10 (net/rds/ib_send.c:282)
  Call Trace:
   <IRQ>
   rds_ib_send_cqe_handler (net/rds/ib_send.c:282)
   poll_scq (net/rds/ib_cm.c:274)
   rds_ib_tasklet_fn_send (net/rds/ib_cm.c:294)
   tasklet_action_common (kernel/softirq.c:943)
   handle_softirqs (kernel/softirq.c:573)
   run_ksoftirqd (kernel/softirq.c:479)
   </IRQ>
  Kernel panic - not syncing: Fatal exception in interrupt

Handle the masked atomic opcodes in the same case as the non-masked
ones: they map to the same struct rds_message.atomic union member, so
the existing container_of()/rds_ib_send_unmap_atomic() body is correct
for them.

Weakness: CWE-476 (NULL Pointer Dereference)

## Which versions are affected by CVE-2026-52939?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2026-52939?

Apply the vendor's patch.

## Is CVE-2026-52939 being exploited?

There is no known exploitation of CVE-2026-52939 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-2026-52939 and fix it if it is affected.

What it is: CVE-2026-52939 is a medium-severity vulnerability in Linux kernel, published on 24 Jun 2026. 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-2026-52939 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-2026-52939/ (Markdown: https://insights.sbomify.com/CVE-2026-52939/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-52939
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-52939
- OSV: https://osv.dev/vulnerability/CVE-2026-52939

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-52939/
Summaries are generated and may contain mistakes; the official description above is the record.