---
cve: "CVE-2021-47515"
severity: "HIGH"
cvss: 7.5
epss: "0.7%"
vendor: "Linux"
kev: false
exploited: false
published: "2024-05-24 15:15:12"
tags: [cve, security, high]
source: tsecurity.de CVE-Dossier
exported: "2026-10-07T03:28:58+02:00"
---

# CVE-2021-47515

> 7.5 HIGH

## Beschreibung

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

seg6: fix the iif in the IPv6 socket control block

When an IPv4 packet is received, the ip_rcv_core(...) sets the receiving
interface index into the IPv4 socket control block (v5.16-rc4,
net/ipv4/ip_input.c line 510):

    IPCB(skb)->iif = skb->skb_iif;

If that IPv4 packet is meant to be encapsulated in an outer IPv6+SRH
header, the seg6_do_srh_encap(...) performs the required encapsulation.
In this case, the seg6_do_srh_encap function clears the IPv6 socket control
block (v5.16-rc4 net/ipv6/seg6_iptunnel.c line 163):

    memset(IP6CB(skb), 0, sizeof(*IP6CB(skb)));

The memset(...) was introduced in commit ef489749aae5 ("ipv6: sr: clear
IP6CB(skb) on SRH ip4ip6 encapsulation") a long time ago (2019-01-29).

Since the IPv6 socket control block and the IPv4 socket control block share
the same memory area (skb->cb), the receiving interface index info is lost
(IP6CB(skb)->iif is set to zero).

As a side effect, that condition triggers a NULL pointer dereference if
commit 0857d6f8c759 ("ipv6: When forwarding count rx stats on the orig
netdev") is applied.

To fix that issue, we set the IP6CB(skb)->iif with the index of the
receiving interface once again.

## CISA-Anreicherung (vulnrichment/ADP)

- CISA-SSVC (Coordinator, v2.0.3):
  - Exploitation: **none**
  - Automatable: **no**
  - Technical Impact: **partial**

## CVSS-Vektor

```
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |
| S Scope | Unverändert | good |
| C Vertraulichkeit | Keine | good |
| I Integrität | Keine | good |
| A Verfügbarkeit | Hoch | bad |

## BSI-Hinweise (deutsch)

- [Linux Kernel: Mehrere Schwachstellen ermöglichen Denial of Service und unspezifische Angriffe](https://wid.cert-bund.de/portal/wid/sicherheitshinweis/WID-SEC-W-2024-1235)

## Referenzen

- <https://git.kernel.org/stable/c/b16d412e5f79734033df04e97d7ea2f50a8e9fe3>
- <https://git.kernel.org/stable/c/6431e71093f3da586a00c6d931481ffb0dc2db0e>
- <https://git.kernel.org/stable/c/ef8804e47c0a44ae106ead1740408af5ea6c6ee9>
- <https://git.kernel.org/stable/c/666521b3852d2b2f52d570f9122b1e4b50d96831>
- <https://git.kernel.org/stable/c/98adb2bbfa407c9290bda299d4c6f7a1c4ebd5e1>
- <https://git.kernel.org/stable/c/ae68d93354e5bf5191ee673982251864ea24dd5c>

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/sicherheitsluecken/cve-2021-47515/) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI WID (CSAF)_