CVE-2021-47515

MEDIUM
Published May 24, 2024 Modified Sep 24, 2025 CWE-476

Description

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.

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CVSS v3.1 Score

5.5
MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Weakness Type (CWE)

CWE-476 CWE-476

Affected Products

Vendor Product
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel
linux linux_kernel

References

Advisories & Patches

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

Frequently Asked Questions

What is CVE-2021-47515? +
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. It has a CVSS v3.1 base score of 5.5 (MEDIUM).
How severe is CVE-2021-47515? +
CVE-2021-47515 has a CVSS v3.1 score of 5.5 out of 10, rated MEDIUM. This is a medium-severity vulnerability that should be remediated as part of regular maintenance.
What products are affected by CVE-2021-47515? +
CVE-2021-47515 affects products from linux, specifically: linux_kernel. Check the affected products table above for specific version ranges.
How do I check if I'm vulnerable to CVE-2021-47515? +
You can use Secably's free Website Scanner to check your website for known vulnerabilities. For infrastructure scanning, use the Port Scanner to identify exposed services that may be affected. Check the vendor advisories linked above for specific patch and version information.

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