CVE-2021-20314: Remote stack buffer overflow in libspf2

                #### Description

#### Attack type

Remote

#### Impact

(x) Code Execution (x) Denial of Service

#### Attack vector(s):

#### Patch

The issue has been fixed in github commit c37b7c1:

https://github.com/shevek/libspf2/commit/c37b7c13c30e225183899364b9f2efdfa85552ef

#### Discoverer(s)/Credits

Philipp Jeitner and Haya Shulman, Fraunhofer SIT

philipp.jeitner () sit fraunhofer de
haya.shulman () sit fraunhofer de

#### Reference(s)

 - libspf2: https://www.libspf2.org/, https://github.com/shevek/libspf2

#### Details and information to reproduce the vulnerability

To reproduce, set the SPF record of a domain you control like listed below:

    example.com. 300    IN      TXT     "v=spf1 exp=exp.example.com"

    # spfquery --sender someone () example com -ip 1.2.3.4
    *** stack smashing detected ***: terminated
    Aborted (core dumped)