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CVE-2021-47515

Disclosure Date: May 24, 2024 •
CVE-2021-47515
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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 Severity and Metrics
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Impact Score:
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General Information

Offensive Application
Unknown
Utility Class
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Ports
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OS
Unknown
Vulnerable Versions
Linux b16d412e5f79
Linux 6431e71093f3
Linux ef8804e47c0a
Linux not down converted
Prerequisites
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Discovered By
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PoC Author
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Metasploit Module
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Reporter
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Vendors

  • Linux

Products

  • Linux
Technical Analysis