# CVE-2021-46955: openvswitch: fix stack OOB read while fragmenting IPv4 packets

> A stack out-of-bounds read in the Linux kernel's Open vSwitch module during IPv4 fragmentation can cause a crash or leak kernel memory.

- **Severity:** High 8.2 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:L/I:N/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 27 Feb 2024
- **Updated:** 5 Aug 2026
- **Also known as:** DEBIAN-CVE-2021-46955, GHSA-6mwq-mrw3-3m6c, UBUNTU-CVE-2021-46955

## What is CVE-2021-46955?

CVE-2021-46955 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

In the Linux kernel, the following vulnerability has been resolved:

openvswitch: fix stack OOB read while fragmenting IPv4 packets

running openvswitch on kernels built with KASAN, it's possible to see the
following splat while testing fragmentation of IPv4 packets:

 BUG: KASAN: stack-out-of-bounds in ip_do_fragment+0x1b03/0x1f60
 Read of size 1 at addr ffff888112fc713c by task handler2/1367

 CPU: 0 PID: 1367 Comm: handler2 Not tainted 5.12.0-rc6+ #418
 Hardware name: Red Hat KVM, BIOS 1.11.1-4.module+el8.1.0+4066+0f1aadab 04/01/2014
 Call Trace:
  dump_stack+0x92/0xc1
  print_address_description.constprop.7+0x1a/0x150
  kasan_report.cold.13+0x7f/0x111
  ip_do_fragment+0x1b03/0x1f60
  ovs_fragment+0x5bf/0x840 [openvswitch]
  do_execute_actions+0x1bd5/0x2400 [openvswitch]
  ovs_execute_actions+0xc8/0x3d0 [openvswitch]
  ovs_packet_cmd_execute+0xa39/0x1150 [openvswitch]
  genl_family_rcv_msg_doit.isra.15+0x227/0x2d0
  genl_rcv_msg+0x287/0x490
  netlink_rcv_skb+0x120/0x380
  genl_rcv+0x24/0x40
  netlink_unicast+0x439/0x630
  netlink_sendmsg+0x719/0xbf0
  sock_sendmsg+0xe2/0x110
  ____sys_sendmsg+0x5ba/0x890
  ___sys_sendmsg+0xe9/0x160
  __sys_sendmsg+0xd3/0x170
  do_syscall_64+0x33/0x40
  entry_SYSCALL_64_after_hwframe+0x44/0xae
 RIP: 0033:0x7f957079db07
 Code: c3 66 90 41 54 41 89 d4 55 48 89 f5 53 89 fb 48 83 ec 10 e8 eb ec ff ff 44 89 e2 48 89 ee 89 df 41 89 c0 b8 2e 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 35 44 89 c7 48 89 44 24 08 e8 24 ed ff ff 48
 RSP: 002b:00007f956ce35a50 EFLAGS: 00000293 ORIG_RAX: 000000000000002e
 RAX: ffffffffffffffda RBX: 0000000000000019 RCX: 00007f957079db07
 RDX: 0000000000000000 RSI: 00007f956ce35ae0 RDI: 0000000000000019
 RBP: 00007f956ce35ae0 R08: 0000000000000000 R09: 00007f9558006730
 R10: 0000000000000000 R11: 0000000000000293 R12: 0000000000000000
 R13: 00007f956ce37308 R14: 00007f956ce35f80 R15: 00007f956ce35ae0

 The buggy address belongs to the page:
 page:00000000af2a1d93 refcount:0 mapcount:0 mapping:0000000000000000 index:0x0 pfn:0x112fc7
 flags: 0x17ffffc0000000()
 raw: 0017ffffc0000000 0000000000000000 dead000000000122 0000000000000000
 raw: 0000000000000000 0000000000000000 00000000ffffffff 0000000000000000
 page dumped because: kasan: bad access detected

 addr ffff888112fc713c is located in stack of task handler2/1367 at offset 180 in frame:
  ovs_fragment+0x0/0x840 [openvswitch]

 this frame has 2 objects:
  [32, 144) 'ovs_dst'
  [192, 424) 'ovs_rt'

 Memory state around the buggy address:
  ffff888112fc7000: f3 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffff888112fc7080: 00 f1 f1 f1 f1 00 00 00 00 00 00 00 00 00 00 00
 >ffff888112fc7100: 00 00 00 f2 f2 f2 f2 f2 f2 00 00 00 00 00 00 00
                                         ^
  ffff888112fc7180: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  ffff888112fc7200: 00 00 00 00 00 00 f2 f2 f2 00 00 00 00 00 00 00

for IPv4 packets, ovs_fragment() uses a temporary struct dst_entry. Then,
in the following call graph:

  ip_do_fragment()
    ip_skb_dst_mtu()
      ip_dst_mtu_maybe_forward()
        ip_mtu_locked()

the pointer to struct dst_entry is used as pointer to struct rtable: this
turns the access to struct members like rt_mtu_locked into an OOB read in
the stack. Fix this changing the temporary variable used for IPv4 packets
in ovs_fragment(), similarly to what is done for IPv6 few lines below.

Weakness: CWE-125 (Out-of-bounds Read)

## Which versions are affected by CVE-2021-46955?

It affects 1 product.


Products: Linux kernel.

## How do I fix CVE-2021-46955?

Apply the vendor's patch.

## Is CVE-2021-46955 being exploited?

There is no known exploitation of CVE-2021-46955 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-2021-46955 and fix it if it is affected.

What it is: CVE-2021-46955 is a high-severity memory corruption vulnerability in Linux kernel, published on 27 Feb 2024. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2021-46955 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-2021-46955/ (Markdown: https://insights.sbomify.com/CVE-2021-46955/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2021-46955
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2021-46955
- OSV: https://osv.dev/vulnerability/CVE-2021-46955

---
From sbomify Insights: https://insights.sbomify.com/CVE-2021-46955/
Summaries are generated and may contain mistakes; the official description above is the record.