Incorrect checksum calculation for UDP packet with ipv6 extension header

["Hupfer, Michael via Wireshark-dev" <wireshark-dev () wireshark org>]

Please see packet 4 of the atached capture

In my opinion checksum 0xc343 is actually correct, since it is calculated using the final destination address 
4ea1:2222:2222::11, but wireshark reports 0x2e12 as correct, which is the result of the checksum calculation if the 
address from the extension header 505:505:505:505:505:505:505:505 is used.

Please refer to RFC 2460:


        If the IPv6 packet contains a Routing header, the Destination
         Address used in the pseudo-header is that of the final
         destination.  At the originating node, that address will be in
         the last element of the Routing header; at the recipient(s),
         that address will be in the Destination Address field of the
         IPv6 header.

In addition, the Linux kernel accepts the UDP packet.

3.4.6 (v3.4.6-0-g6357ac1405b8)

Compiled (64-bit) with Qt 5.15.2, with libpcap, with GLib 2.52.3, with zlib
1.2.11, with SMI 0.4.8, with c-ares 1.15.0, with Lua 5.2.4, with GnuTLS 3.6.3
and PKCS #11 support, with Gcrypt 1.8.3, with MIT Kerberos, with MaxMind DB
resolver, with nghttp2 1.39.2, with brotli, with LZ4, with Zstandard, with
Snappy, with libxml2 2.9.9, with QtMultimedia, with automatic updates using
WinSparkle 0.5.7, with AirPcap, with SpeexDSP (using bundled resampler), with
Minizip.

Running on 64-bit Windows 10 (2009), build 19043, with Intel(R) Core(TM)
i7-8665U CPU @ 1.90GHz (with SSE4.2), with 32483 MB of physical memory, with
locale German_Germany.utf8, with light display mode, without HiDPI, with Npcap
version 1.31, based on libpcap version 1.10.1-PRE-GIT, with GnuTLS 3.6.3, with
Gcrypt 1.8.3, with brotli 1.0.2, without AirPcap, binary plugins supported (21
loaded).

Built using Microsoft Visual Studio 2019 (VC++ 14.28, build 29910).

Attachment: Client_UDP_ExtHead_2021-05-25.pcapng
Description: Client_UDP_ExtHead_2021-05-25.pcapng

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