Package: opendkim Version: 2.9.2-2 Severity: important Tags: patch
OpenDKIM, or more precisely, libopendkim up to 2.10.3 fails to canonicalize folded mail headers according to the RFC 6376 "relaxed" algorithm when a header is folded (wrapped) right after the ":" as for instance in | Subject:\r\n | long subject text continued on subsequent lines ... https://tools.ietf.org/html/rfc6376#section-3.4 Section 3.4.2 requires that this is canonicalized into | subject:long subject text continued on subsequent lines ... but libopendkim produces (note the single space after ":") | subject: long subject text continued on subsequent lines ... Hence, DKIM signatures derived from such headers are broken for all systems other than OpenDKIM (up to and including 2.10.3), and OpenDKIM fails to verify valid signatures produced by systems other than OpenDKIM. For the "From:" header this has been reported upstream at #226 Bad signature of From:\r\n wrapped field https://sourceforge.net/p/opendkim/bugs/226/ but the bug affects canonicalization in general. The provided patches are trivial, see DEP-3 patch by A. Schulze at https://sourceforge.net/p/opendkim/bugs/_discuss/thread/d08319d2/bd34/attachment/ticket226.patch Quoting thereof for reference: -- dv-opendkim-2.10.3.orig/libopendkim/dkim-canon.c +++ dv-opendkim-2.10.3/libopendkim/dkim-canon.c @@ -388,7 +388,7 @@ dkim_canon_header_string(struct dkim_dst /* skip all spaces before first word */ - while (*p != '\0' && DKIM_ISWSP(*p)) + while (*p != '\0' && DKIM_ISLWSP(*p)) p++; The patch was applied upstream in opendkim-2.11.0.Alpha0 as of 2015-10-22. I was not yet able to assess which or how many mailers produce headers that wrap immediately after the header keyword. However, I want to mention that Debian's default configuration of OpenDKIM as in Jessie and Stretch is unfortunately more likely to produce invalid signatures due to the fact that headers such as "References:" and "In-Reply-To:" which are often wrapped are signed. This is a default setting by OpenDKIM left unchanged by Debian, cf. opendkim.conf(5) + https://tools.ietf.org/html/rfc6376#section-5.4 So, signers can somewhat mitigate this bug's consequences using "OmitHeaders". Receivers, though, need to apply the patch. -- System Information: Debian Release: 7.11 APT prefers oldstable-updates APT policy: (990, 'oldstable-updates'), (990, 'oldstable'), (500, 'stable') Architecture: amd64 (x86_64) Versions of packages opendkim depends on: ii adduser 3.113+nmu3 ii libbsd0 0.4.2-1 ii libc6 2.19-18+deb8u6 ii libdb5.3 5.3.28-9 ii libldap-2.4-2 2.4.31-2+deb7u2 ii liblua5.1-0 5.1.5-4+deb7u1 ii libmemcached11 1.0.18-4 ii libmemcachedutil2 1.0.18-4 ii libmilter1.0.1 8.14.4-4+deb7u1 ii libopendbx1 1.4.6-8 ii libopendkim9 2.9.2-2 ii librbl1 2.9.2-2 ii libssl1.0.0 1.0.1t-1+deb8u5 ii libunbound2 1.4.17-3+deb7u2 ii libvbr2 2.9.2-2 ii lsb-base 4.1+Debian8+deb7u1 opendkim recommends no packages. Versions of packages opendkim suggests: ii opendkim-tools 2.9.2-2 -- Configuration Files: /etc/opendkim.conf changed [not included] -- no debconf information
