# CVE-2021-47238: net: ipv4: fix memory leak in ip_mc_add1_src

> A memory leak in the Linux kernel's IPv4 multicast source handling allows local attackers to exhaust system memory, causing denial of service.

- **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:** 21 May 2024
- **Updated:** 23 May 2026
- **Also known as:** DEBIAN-CVE-2021-47238, GHSA-jv5x-8v9f-frx2, UBUNTU-CVE-2021-47238

## What is CVE-2021-47238?

CVE-2021-47238 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 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:

net: ipv4: fix memory leak in ip_mc_add1_src

BUG: memory leak
unreferenced object 0xffff888101bc4c00 (size 32):
  comm "syz-executor527", pid 360, jiffies 4294807421 (age 19.329s)
  hex dump (first 32 bytes):
    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................
    01 00 00 00 00 00 00 00 ac 14 14 bb 00 00 02 00 ................
  backtrace:
    [<00000000f17c5244>] kmalloc include/linux/slab.h:558 [inline]
    [<00000000f17c5244>] kzalloc include/linux/slab.h:688 [inline]
    [<00000000f17c5244>] ip_mc_add1_src net/ipv4/igmp.c:1971 [inline]
    [<00000000f17c5244>] ip_mc_add_src+0x95f/0xdb0 net/ipv4/igmp.c:2095
    [<000000001cb99709>] ip_mc_source+0x84c/0xea0 net/ipv4/igmp.c:2416
    [<0000000052cf19ed>] do_ip_setsockopt net/ipv4/ip_sockglue.c:1294 [inline]
    [<0000000052cf19ed>] ip_setsockopt+0x114b/0x30c0 net/ipv4/ip_sockglue.c:1423
    [<00000000477edfbc>] raw_setsockopt+0x13d/0x170 net/ipv4/raw.c:857
    [<00000000e75ca9bb>] __sys_setsockopt+0x158/0x270 net/socket.c:2117
    [<00000000bdb993a8>] __do_sys_setsockopt net/socket.c:2128 [inline]
    [<00000000bdb993a8>] __se_sys_setsockopt net/socket.c:2125 [inline]
    [<00000000bdb993a8>] __x64_sys_setsockopt+0xba/0x150 net/socket.c:2125
    [<000000006a1ffdbd>] do_syscall_64+0x40/0x80 arch/x86/entry/common.c:47
    [<00000000b11467c4>] entry_SYSCALL_64_after_hwframe+0x44/0xae

In commit 24803f38a5c0 ("igmp: do not remove igmp souce list info when set
link down"), the ip_mc_clear_src() in ip_mc_destroy_dev() was removed,
because it was also called in igmpv3_clear_delrec().

Rough callgraph:

inetdev_destroy
-> ip_mc_destroy_dev
     -> igmpv3_clear_delrec
        -> ip_mc_clear_src
-> RCU_INIT_POINTER(dev->ip_ptr, NULL)

However, ip_mc_clear_src() called in igmpv3_clear_delrec() doesn't
release in_dev->mc_list->sources. And RCU_INIT_POINTER() assigns the
NULL to dev->ip_ptr. As a result, in_dev cannot be obtained through
inetdev_by_index() and then in_dev->mc_list->sources cannot be released
by ip_mc_del1_src() in the sock_close. Rough call sequence goes like:

sock_close
-> __sock_release
   -> inet_release
      -> ip_mc_drop_socket
         -> inetdev_by_index
         -> ip_mc_leave_src
            -> ip_mc_del_src
               -> ip_mc_del1_src

So we still need to call ip_mc_clear_src() in ip_mc_destroy_dev() to free
in_dev->mc_list->sources.

Weakness: CWE-400 (Uncontrolled Resource Consumption)

## Which versions are affected by CVE-2021-47238?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-47238?

Apply the vendor's patch.

## Is CVE-2021-47238 being exploited?

There is no known exploitation of CVE-2021-47238 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-2021-47238 and fix it if it is affected.

What it is: CVE-2021-47238 is a medium-severity denial of service vulnerability in Linux kernel, published on 21 May 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-2021-47238 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-2021-47238/ (Markdown: https://insights.sbomify.com/CVE-2021-47238/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-47238
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-47238
- OSV: https://osv.dev/vulnerability/CVE-2021-47238

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-47238/
Summaries are generated and may contain mistakes; the official description above is the record.